Secondary legislation regulations and guidelines are being used as the working values against which indoor air quality (IAQ) can be assessed.

It can be regulated via health and safety regulations, such as the Control of Substances Hazardous to Health (COSHH) Regulations (2002), to which all places of work have to adhere. Regulation 6(1) of COSHH states that an employer ‘should carry out a suitable and sufficient assessment of the risks to the health of your employees and any other person who may be affected by your work, if they are exposed to substances hazardous to health’. Regulation 10 of COSHH specifies that monitoring is required ‘when measurement is needed to ensure a workplace exposure limit (WEL) or any self-imposed working standard is not exceeded’.

There are legally binding WEL for around 500 substances, listed in HSE EH40/2005. However, WEL only relate to personal (exposure) monitoring of people at work, are calibrated for a healthy working-age adult, and can’t be readily adapted to evaluate or control prolonged, continuous or non-occupational exposure. So, for most office and education settings – and all public and residential buildings – WEL cannot be used to assess building occupant exposure to IAQ.

New buildings, however, are covered by the recently updated Statutory Instrument Building Regulations (2010). Now included in Approved Document F1 is ‘Means of Ventilation’, providing statutory guidance on ventilation requirements to maintain IAQ.

Within Approved Document F1, Appendix B: Performance-based ventilation, average indoor air pollutant guideline values are set for carbon monoxide (CO), nitrogen dioxide (NO₂), formaldehyde, total volatile organic compounds (TVOC) and ozone (O₃), largely based on World Health Organization (WHO) guidelines. However, as the document relates to building performance guidance, these values are performance criteria of the assessment of ventilation, not occupant exposure assessment criteria.

For several years, regulations, standards and guidance on IAQ for school buildings have been set out in the UK government’s Education and Skills Funding Agency Building Bulletin BB101. This includes guidelines on ventilation, such as setting a maximum CO₂ in teaching spaces, and specific guidelines on IAQ, mainly based on WHO guidelines that ‘should be used for schools’.

The WHO first published air quality guidelines in 1987, which have been updated since. They ‘serve as a global target for national, regional and city governments to work towards improving their citizens’ health by reducing air pollution’.

In 2010, the WHO published guidance on risks associated with pollutants commonly found in indoor air (benzene, CO, formaldehyde, naphthalene, NO₂, polycyclic aromatic hydrocarbons, radon, trichloroethylene and tetrachloroethylene), and updated their (general) air quality guidelines in 2021 (see Table 1).

It should be noted that WHO general air quality guideline values ‘do not differentiate between indoor and outdoor exposure’, so they are applicable indoors. Some of the latest 2021 guidelines supersede its specific 2010 IAQ guidelines (eg, for CO and NO₂).

They are relevant in all countries and in all exposure settings where COSHH WEL are not appropriate. Organisations, including CIBSE, point to these guidelines for IAQ monitoring. In recent years, other organisations have published IAQ guidance.

About the author
Oliver Puddle is technical director at DustScanAQ

The post The good, bad and illegal: rules and guidelines for IAQ appeared first on CIBSE Journal.

The Department of Health and Social Care (DHSC) set up a team to develop up-to-date guidance for landlords, working with a multidisciplinary expert group and advice from the Committee on the Medical Effects of Air Pollutants. The resulting guidance was published on 7 September.

The guidance sets out the responsibilities of landlords, in both the social and private sectors, for ensuring that their accommodation is fit to live in and free from serious hazards, including damp and mould. It makes very clear that they must act with urgency to deal with damp and mould in their dwellings, and must protect their tenants’ health.

It includes guidance on the requirements of the Building Regulations that relate to minimising the risk of damp and mould, and that they apply whenever building work is carried out in the dwelling. The coroner in the Awaab Ishak case found that his family’s flat was not compliant with Building Regulations.

The guidance is very clear that tenants should not be blamed for damp and mould in their home, and that they are absolutely not the result of so-called ‘lifestyle choices’. Washing, showering and doing your laundry are not ‘lifestyle choices’, and any dwelling must be adequately heated and ventilated to prevent them causing damp problems.

Where moisture problems are reported, landlords are required to act quickly to determine the underlying causes, whether they are down to inadequate ventilation or structural faults in the building.

In addition to the new guidance on avoiding damp and mould, the government released further guidance on the Housing Health and Safety Rating System, used to assess the safety of homes and identify and prioritise health and safety risks.

Forthcoming legislation in the Renters (Reform) Bill and the new Social Housing (Regulation) Act 2023, are intended to improve housing standards by:

• Creating a statutory duty on social housing providers to appoint a senior health and safety lead; significant statutory duties to monitor compliance with health and safety provisions and raise compliance risks or failings with senior management (see Section 10 of the 2023 Act)
• Introducing new requirements for landlords to address hazards such as damp and mould in social homes
• Empowering the Housing Ombudsman and changing the law to enable social housing residents to complain directly to the ombudsman
• Reviewing the Decent Homes Standard and applying it to private rented homes for the first time
• Introducing new professional standards and requiring senior housing staff to hold, or work towards, recognised housing management qualifications
• Introducing an ombudsman for private tenants.

Landlords and their health and safety leads need to read this guidance and adopt the best practices it sets out. Those who work in social housing or manage private rented homes would be well advised to read section 10 of the Social Housing Act as well.

In addition to protecting tenants’ health, it will help to prevent a repeat of the utterly avoidable tragedy that befell Awaab Ishak’s family.

The post After Awaab: guidance on protecting tenants’ health appeared first on CIBSE Journal.

A report published in 2022 by the United Nations Environment Programme, Spreading like wildfire: the rising threat of extraordinary landscape fires, forecast that, even if greenhouse gases are reduced, there could be up to a 50% increase in wildfires across the globe by the end of the century, spanning the Arctic and central Europe to tropical rainforests and the Amazon.

Wildfires pose a growing risk to people in homes, offices and other premises through their impact on indoor air quality (IAQ) and, thereby, people’s health. Developing mitigation strategies for maintaining IAQ – including the adaptation or upgrading of air conditioning systems in buildings – is increasingly important.

Over the past two years, record temperatures in the UK and other parts of Europe, combined with long periods of intense heat, have resulted in an unprecedented incidence of severe wildfires. Only last month, a wildfire covering around 40 hectares on Rhigos mountain, in Rhondda Cynon Taf, was one of several in the region that caused significant damage and posed a potential health hazard to locals.

It is anticipated that such fires will become more prevalent; research published by Met Office scientist Matthew Perry in 2022 concluded that wildfires can be considered an ‘emergent risk’ for the UK, and he predicted a large increase in hazardous-fire weather conditions in summer that may extend into autumn. In the US, where wildfires are a perennial issue, data from the Environmental Protection Agency (EPA) suggests there have been large increases in areas burned by wildfires since the 1980s. It estimates that the average area burned in the west of the country will increase by 54% by 2050 as a result of climate change.

The health impact

A recent paper on wildfires (bit.ly/CJBerkWF) from the Indoor Air Quality (IAQ) Scientific Findings Resource Bank of the Lawrence Berkeley National Laboratory (supported by EPA funding) highlights some of the key issues for public health, and potential mitigations through ventilation interventions. In terms of health impact, wildfire smoke can cause large increases in outdoor airborne particles, as well as substantial increases in gaseous air pollutants, such as carbon monoxide, nitrogen dioxide, formaldehyde and acetaldehyde. These can spread over thousands of kilometres, which means forest fires can also have an impact in urban environments, increasing the concentration of fine particles significantly.

According to the EPA, the biggest threat from wildfire smoke is from fine particles (2.5 micrometers in diameter [PM2.5] or less). These can enter the eyes or respiratory system, where they can cause significant health problems, from irritated eyes to lung illnesses and cardiovascular problems. They can be particularly hazardous for older people, young children, and those with underlying health conditions. Researchers (Johnston et al) have estimated that landscape fires, consisting of wildfires and prescribed burns, cause 339,000 premature deaths per year globally.

Wildfire smoke can have serious consequences for human health

As wildfire smoke with fine particulates and gases can enter buildings through natural ventilation, mechanical ventilation and infiltration, preventative measures and mitigation can be effective. Steven J. Emmerich is a mechanical engineer in the Energy and Environment Division at the US’s National Institute of Standards and Technology. He says either the smoke has to be kept out or removed when it gets in. ‘Keeping smoke out can be achieved through the combination of a tight building envelope, maintaining a positive building pressure, reducing outdoor air intake to a minimum and filtering the outdoor air,’ he says.

Apart from the obvious advice of closing doors, vents and windows in the event of a wildfire, the operation of high-efficiency indoor particle filtration systems (see CIBSE air cleaning technologies guidance at www.cibse.org/knowledge) is recommended by the EPA, as well as by members of the UK’s Airbods research group. ‘Removing the PM2.5 when it gets in means using better filtration in recirculating HVAC systems,’ says Emmerich. ‘Many building owners and operators can take advantage of efforts they made to improve building filtration during Covid-19.’

Measures to consider include disabling economisers and demand-control ventilation, verifying what level of improved filtration a building’s systems can employ, and, potentially, rigging temporary filtration of outdoor air intakes.

A number of practical steps to mitigate the impact of wildfire smoke are also recommended by the EPA. If the HVAC system has a fresh air intake, this should be closed or the system turned to recirculation mode. For mechanical ventilation systems, it is important to ensure the correct pre-filters and filters are in place. A MERV 13 filter or one with as high a rating as the system’s fan and filter slot can accommodate is recommended by the EPA (see bit.ly/CJEPAfilter). Filters that can stop finer particulates generated by wildfires – for example, 1 micrometers (PM1) – are available from specialist filtration solution suppliers.

If the building operates an evaporative cooler, this should be avoided in smoky conditions, says the EPA, as it can draw more smoke inside the building. Other options, such as fans or window air conditioners, should be considered.

A portable air cleaning solution can also be effective in mitigating the impact of smoke. Among studies mentioned in the Berkeley Lab paper, two found that air cleaners in homes reduced PM2.5 by around 65%, and by 63% to 88%, during wildfires.

Preparing for the impact of wildfires is very important, and ASHRAE has published a framework that Emmerich says offers practical help with an often overlooked aspect – making a plan. ‘Part of that is returning to normal operations after the wildfire smoke episode is over,’ he says.

Australian wildfires: health impacts

Australia’s ‘Black Summer‘ of wildfires in 2019-20 was one of the worst wildfire seasons on record, causing immense destruction – and the full impact on health from smoke is still being assessed by researchers. The fires in eastern Australia consumed 24 million hectares of land and killed 33 people, with the resulting smoke estimated to have contributed to a further 429 deaths.

Studies looking at the impact of smoke inhalation in Australia and the US indicate that wildfire smoke can lead to premature labour, low birth weight, impaired lung development, and higher use by children of some prescription drugs. Studies in Australia is looking into the long-term impacts of these wildfires; one doctor told Bloomberg (bit.ly/CJWFhealth23) that, at the height of Black Summer, walking in Sydney would have been equivalent to smoking 37 cigarettes in a day

The post Protecting building occupants from wildfire smoke appeared first on CIBSE Journal.

The previous Guide M, published in 2014, primarily focused on health and comfort, but missed crucial aspects related to wellbeing. For example, it lacked guidance on infection control, lighting and daylight, water quality, noise and vibration, and electric and magnetic fields. 

These elements greatly influence the perception of comfort within a space and can have a chronic impact on occupant health, even if not immediately noticeable. For instance, poor indoor air quality (IAQ) over a prolonged period can be detrimental to health. Noise, often perceived as distracting, was not adequately addressed in the 2014 version. 

To rectify these gaps, the latest iteration of Guide M expands its scope to encompass the various dimensions of the Well Building Standard and other assessment schemes. It reflects how carbon dioxide levels have gained prominence as an indicator of ventilation rates, where high levels suggest increased occupancy and the need for improved ventilation. 

Building occupant choice and awareness play crucial roles, particularly for office space providers, such as WeWork, Regus and so on, where the wellbeing of high-end leaseholders is a priority for clients. 

The primary driving force behind measures in commercial premises is the creation of a comfortable, productive environment and the enhancement of property value. Although studies suggest that improved conditions lead to increased productivity, proving causality remains challenging for engineers.

The new Guide M addresses IAQ for FMs, offering a comprehensive understanding of the subject. Changes in building function and agile working patterns are acknowledged, recognising that individuals are no longer tied to specific desks or offices.

Technical information from TM40 and TM62-64 has been integrated into Guide M. However, to avoid potential discrepancies, tables on ventilation and noise levels from Guide A were not replicated. Signalling this connection is key to ensure consistency and prevent Guide M from becoming outdated if Guide A is updated.

Guide M places a strong emphasis on enhancing health and wellbeing in buildings. By focusing on engineering aspects and addressing gaps from previous versions, it aims to provide a comprehensive framework for creating comfortable and safe environments that promote productivity and support occupant health.

It acknowledges the significance of compliance and anticipates a rise in demands for evidence of adherence to standards. Tragic incidents, such as the death of Awaab Ishak caused by mould, highlight the importance of ventilation. While the incident occurred in a non-commercial building, it emphasises the critical role ventilation plays in ensuring occupant safety and wellbeing. 

With the Health and Safety Executive taking a regulatory role under the Building Safety Act, it will have the authority to investigate areas beyond traditional health and safety concerns, where aspects of wellbeing will come under greater regulatory scrutiny.

• Guide M will launch in September and be available at www.cibse.org/knowledge

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Activities such as cooking and cleaning can produce high pollutant concentrations, with potential impacts on human health, including respiratory and cardiovascular diseases^2,3. However, environmental regulation still focuses on outdoor air quality, with the exception of specific occupational exposures⁴.

A joint project between the universities of York, Chester and Nottingham has studied the production of different chemicals during cooking and cleaning. The Impeccable (Impacts of cooking and cleaning on indoor air quality: towards healthy buildings for the future) project used state-of-the-art equipment, coupled with computational modelling¹¹ to understand the complex underlying chemistry that occurs during and after domestic cooking and cleaning activities.

The study recommends the most effective ventilation strategies to reduce the air pollution created by cooking and cleaning.

The climate emergency has forced us to think more carefully about energy efficiency. Buildings are becoming increasingly airtight, but we have the potential to increase our exposure to indoor air pollution if sources such as cooking and cleaning dominate our personal exposure to air pollution.

Measuring VOCs while cooking in the home lab

We need to understand the sources and reactions of pollutants indoors, particularly as an increasing weight of evidence shows that secondary pollutants are more harmful to health than primary emissions⁹. For instance, the carcinogen formaldehyde is a reaction product of limonene oxidation, the latter species being a key component of many cleaning formulations¹⁰.

Cooking generates high concentrations of particulate matter (PM), nitrogen oxides (NOX) and carbon monoxide (CO). Emission rates depend on the cooking method, and oil and food types.

Emissions of PM are higher for frying than boiling and steaming, and higher when you fry meat compared with vegetables². During cooking, PM concentrations can reach several hundred mg/m³, particularly when frying², exceeding acute health standards over several hours⁵. Cooking can also generate ultra-fine particles (< 100 nm in diameter), which are associated with adverse effects on the respiratory and cardiovascular systems⁶.

Cleaning is another regular activity indoors, with bleach cleaning having a large impact on gas-phase and surface chemistry⁷. The prevalence of asthma among domestic cleaning staff suggests that cleaning activities may cause adverse health effects⁸.

The Impeccable project

The experiments undertaken range from benchtop ones in a lab to determine specific emission rates from individual products or processes, through to more realistic settings, where full meals are cooked in a more home-like environment.

Measurements are taken using on- and off-line diagnostics, to determine types and quantities of various indoor air pollutants. Selected-ion flow-tube mass spectrometry (SIFT-MS) was used to measure real-time concentrations of more than 40 volatile organic compounds (VOCs) during the cooking and cleaning experiments.

This technique uses a plasma to generate ions, which then ionise VOCs present in the sample gas¹². These charged species are then separated and quantified based on their mass-to-charge ratios. An example of the real-time data obtained during a cooking experiment is shown in Figure 1.

The modelling of indoor air chemistry has been carried out using INCHEM-Py, an open-source box model that uses a detailed chemical mechanism, combined with parameterisation for indoor-outdoor exchange, gas-particle partitioning, surface deposition, and internal photolysis¹³.

The detailed model allows us to simulate the time-evolved concentrations not only of the species emitted from indoor activities, but also of those formed after chemical reactions, such as formaldehyde, peroxyacylnitrate species (PANs) and PM.

The simulated concentrations of some secondaries formed after the typical stir-fry cooking experiment are shown in Figure 2. These products are often more harmful to human health than the original emissions, so understanding how they are produced can help inform scientifically rigorous mitigation measures (such as extraction of cooking fumes or increased ventilation).

Relevance for building design and operation

Kitchen ventilation is regulated by Approved Document F of the Building Regulations in England. In new houses, there is a requirement for a cooker hood that extracts to the outside or a wall-mounted fan.

The advantage of the cooker hood is that it captures cooking contaminants before they mix in the kitchen, whereas the wall fan allows the contaminants to mix before they are extracted. The required flowrate through the hood is half that of the fan, which implies that it should capture 50% of all emitted contaminants. This is known as a capture efficiency. There is no requirement to test hoods to make sure they meet this requirement, although there is now an ASTM standard¹⁴ that tests some types of hood in a laboratory environment. Future versions of Approved Document F should require cooker hoods to conform to the ASTM standard or allocate a punitive capture efficiency to those that are untested.

Ventilating for 10 minutes after cooking has finished has a significant effect on exposure and should be recommended by public health campaigns^15,16. The higher airflow rate through the wall fan means that it reduces the concentration of contaminants in the air faster than the hood. So having multiple flowrate settings on a hood is advantageous. The best place to locate a hood is against a wall, between cabinets, directly over the gas burners/hob, and as close to the burners as the manufacturer allows. Noise is often a barrier to their use, so using short, wide, straight, rigid, noise-absorbing ducts that reduce air velocity to 2-3 m/s is best practice.

When cooking, using the back burners increases the pollutant capture efficiency¹⁶. Consider using the hood, at least on low speed, for general kitchen ventilation when using other appliances, such as toasters.

Using induction rather than gas burners, and electric rather than gas ovens, reduces the emission of nitrogen dioxide (NO₂), but the chronic harm from exposure to NO₂ is significantly less than that from fine PM. A good cooker hood will capture NO₂ from a burner, so using the hood is more important than changing from a gas to an induction stove.

In very airtight homes (<1 m³/h/m²) make-up air into the kitchen or home is needed and this can be provided using mechanical ventilation with heat recovery (MVHR). Reclaiming thermal energy from the exhaust stream can be problematic in MVHR systems because grease can clog the heat exchanger. This problem has yet to be solved and may require more frequent cleaning of filters.

Some homes have recirculating fans, which pass air through a particle filter and resupply it into the kitchen, rather than exhaust it outside. In this instance, it is imperative to use induction hobs. Electric hobs have their own complications because they can emit PM when they get dirty. For homes that have no fans in their kitchens, windows and doors should be opened when cooking and cleaning to provide ventilation in the short term. In the medium term, a mechanical system should be installed and trickle ventilators kept open at all times.

We would like to thank EPSRC for funding for the Impeccable project (EP/T014474/1).

About the authors
Professor Nicola Carslaw is professor of indoor air chemistry in the Department of Environment and Geography at the University of York

Dr Helen Davies is research associate in chemistry in the Department of Environment and Geography at the University of York

Dr Benjamin Jones associate professor in the Department of Architecture and Built Environment at the University of Nottingham.

References

1. Nazaroff, W. W.; Goldstein, A. H., (2015), Indoor Air, 25, (4), 357-61
2. Abdullahi, K.L. et al. (2013), Atmos. Environ. 71, 260-294
3. Wolkoff, P. (2013) Int. J. Hygiene Env. Health, 216, 371-394
4. Weschler, C.J., and N. Carslaw, Environ. Sci. Technol., 2018, 52, 2419-2428
5. Logue, J.M., et al. (2011), Indoor Air, 21, 92-109
6. Rim, D. et al. (2013), Environ. Sci. Technol., 47, 1922-1929
7. Wong, J. P. S et al. (2017) Indoor Air, 27, 1082-1090
8. Medina-Ramón, M. et al. (2006) Occupational and Environmental Medicine, 62, 598-606
9. Buchanan, I.S.H. et al. (2008), Indoor Air 18, 144-155
10. Wang, C., M., et al. Environ. Sci. Proc. Impacts, 2017, DOI: 10.1039/C6EM00569A
11. Impeccable website: impeccable.york.ac.uk
12. Smith, D., Španel, P., (2005), Mass Spectrometry Reviews, 24, 661-700
13. Shaw et al. (2021). Journal of Open Source Software, 6(63), 3224, doi.org/10.21105/joss.03224
14. ASTM, Measuring Capture Efficiency of Domestic Range Hoods. Report. 2018.
15. Holgate S et al. The inside story: Health effects of indoor air quality on children and young people. Royal College of Paediatrics and Child Health; 2020.
16. O’Leary C, et al. Setting the standard: The acceptability of kitchen ventilation for the English housing stock. Building and Environment. 2019:106417.

The post A recipe for good IAQ: the impact of cooking and cleaning on indoor environments appeared first on CIBSE Journal.

Air purification or cleaning devices have been discussed as a solution, as they provide a localised and decentralised means of ventilation without the need for large plant and distribution systems.

Leeds Beckett University’s Lewis Turner investigated the performance of air purification systems to reduce infection. His paper, Efficacy of air purification to control infection in NHS hospitals, looked to benchmark air purifiers against currently used mechanical and natural ventilation techniques within an NHS hospital ward scenario (as shown in Figure 1). Last month, the paper was runner-up in REHVA’s student competition.

In Turner’s scenario, there are four males on the ward: person one is infected with a respiratory virus and has symptomatic coughing, while the others are not infected but are susceptible to infection.

Two air purifiers (AP) were studied, one representing a ‘healthcare grade’ system and the other a ‘domestic’ system (as shown in Figure 2). The healthcare air purifier (AP-H) had a ‘side in, top out’ flowrate of 520 m³.h^-1 and a maximum aerosol efficiency of 99.728%. The domestic air purifier (AP-D) had a maximum flowrate of 190 m³.h^-1 and maximum aerosol efficiency of 99.82%. In the scenario, the air purifiers were located on the floor, to the right of person one.

Lewis modelled the risk of infection and developed a computational fluid dynamics (CFD) model to investigate the pathogen airflow characteristics, benchmarking the APs against the mechanical and natural ventilation systems. The mechanical ventilation ductwork system in Figure 2 provides balanced ventilation of six air changes per hour with a volume flowrate of 528 m³.h^-1. The natural ventilation was provided through the openable windows and with average wind speeds and window opening, the study used an average fresh airflow rate of 185 m³.h^-1.

The infection risk mathematical modelling calculated the probability of susceptible people catching an infection when in the same ventilated space as infectious people. The CFD study simulated cough particulates travelling through air and how they interacted with the ventilation systems. Person 1 was simulated sitting up in bed, coughing 3.13 e^-8kg of Covid-19-infected aerosol into the zone within a period of 0.5s at 90º to their face, with a velocity of 10m.s^-1 from a 4cm² mouth positioned 590mm above the bed. Cough particulate had a randomised diameter of between 2.5mm and 200mm, consisting of liquid water. The natural ventilation was not simulated because of the chaotic nature of the airflow.

Around 85% of visits to emergency departments are less than four hours long, so the study focused on the number of subsequently infected patients under typical circumstances, across a four-hour period.

The infection risk mathematical modelling results, shown in Figure 3, indicate similarities in performance of AP-D and natural ventilation, with a performance differential of 10.7% in favour of AP-D. AP-D and natural ventilation have a comparable flowrate, but have different mixing factors of 2 and 2.5 respectively. The mixing factor has a significant impact on performance because it defines how well fresh air dilutes the pathogen. This impact is higher for natural ventilation because of unpredictable natural airflow currents, which cause ineffective mixing. For AP-D, the airflow (treated and supplied by AP-D) is directed into the zone at a constant level and can mix effectively with the internal air.

The study identified that the higher mixing factor for the APs results in a 29% higher infection probability, with the lack of fresh air supply contributing to the poor performance of the air purifiers to control infection. Both APs dilute pathogens with greater performance than natural ventilation.

The CFD study generated three sets of data, two of which are shown in Table 1. These indicate that mechanical ventilation has the highest performance. The APs do, however, present some efficacy for infection control as they reduce the particulate mass to 5% in less than 13 seconds (mechanical ventilation can reduce it to 5% in 4 seconds). All ventilation systems fail to remove a majority of the infectious particulate, which means much of the particulate is still present on walls and surfaces, and can sustain for multiple days, depending on the material.

Figure 4 presents the third set of data from the CFD simulation – the maximum penetration distance of particles within the zone from person 1. The data has been compared with the distance of each susceptible person to identify if particles could potentially come into contact with them. It is assumed that 1.25e^-9 kg of particulate mass represents an infectious load of Covid-19, so greater than 1.25e^-9 kg indicates a higher infection risk and less than 1.25e^-9 kg indicates a lower infection risk. Overall, mechanical ventilation has the highest performance, with only one susceptible person potentially inhaling an infectious load. There were three potential infectious-load inhalations for AP-H and two for AP-D.

The results identified that all ventilation systems fail to effectively remove infectious particulate from the zone, with most of the particulate that remained found on the ward’s walls and surfaces. Particles become scattered and, consequently, miss the intake to the APs and contact the air purifier body and surrounding surfaces.

These findings indicate that the size of intake to each system impacts the total escaped mass – and as the air purifiers have a smaller particle extraction capture area, they cannot remove as much mass as the mechanical ventilation system.

The results identified that AP-H and AP-D fail to control the penetration of infectious particulate effectively, whereas the mechanical ventilation system can control particulate with much higher effectiveness.

This issue seems to be amplified by the low position of the air purification devices, as the supply from the APs is much closer to the injection point than the AP intake. As the particles move to be drawn in by the AP, they are likely to be impacted by the turbulent upward airflow from the AP. Additionally, the short-circuiting between AP intake and supply can reduce their efficacy, as further penetrated particles cannot be drawn into the APs. This does not occur in mechanical ventilation because of the effective air distribution throughout the zone.

AP-H is found to exceed the performance of AP-D throughout the infection probability modelling, and the CFD results seem to corroborate these results.

Lewis concludes that these air purifiers have a higher performance than natural ventilation and should be considered for hospitals where mechanical ventilation is not available. However, he notes that air purifiers cannot perform to the level of standard mechanical ventilation, so should not be used as an alternative.

The post Hospital ventilation: can air purification systems provide relief? appeared first on CIBSE Journal.

There is an increasing recognition of the role the built environment plays in people’s health and wellbeing. A wide range of health determinants are contingent on the quality of the built environment, including neighbourhood conditions, green infrastructure, and outdoor and indoor environmental quality. 

It is expected that health inequalities will be exacerbated by the ongoing cost of living crisis. Due to a hike in energy prices, a reduction in disposable income and low thermal efficiency levels of the housing stock, almost a quarter of UK households are now facing fuel poverty, with large families, lone parents and pensioner couples being most affected.^2,3 

Many people in deprived population groups are having to choose between eating or heating their homes. Beyond the impacts of rising fuel costs on health and wellbeing, there are also interactions between building energy efficiency and building services, financial choices, occupant behaviour, IAQ, and comfort. 

One example is the increase in mould risk due to reduced heating. English Housing Survey assessments say that damp and mould risk is almost four times higher for the poorer quintile group compared to the wealthiest group.¹

Another example is the emerging trend of switching to solid fuel heating. The rapid rise in domestic burning of solid fuels, such as wood, for heating, can deteriorate both outdoor and indoor air quality.⁴ 

Currently, there is lack of financial mechanisms to support the installation of energy efficiency measures. According to a recent letter by the Climate Change Committee, the number of government installations of energy efficiency measures fell from 2.3 million a decade ago to fewer than 100,000 in 2021.⁵

While it is imperative that we decarbonise our building stock, single focus policies can potentially lead to unintended consequences, if other aspects of building performance are neglected. 

As our buildings become more thermally insulated and airtight in the path towards net zero, ‘unintended ventilation’ air exchange paths will be diminished. Unless energy efficiency interventions are combined with sufficient means of controlled ventilation, this could lead to air pollutants and heat trapped indoors. 

A recent BMJ paper called for empirical longitudinal data to be collected in energy efficient buildings, to quantify the effects of low carbon measures on health and inequalities.⁶ 

The effects of outdoor air pollution are not equally distributed: it is estimated, for example, that 46% of the most deprived London areas experience NO₂ concentrations above the recommended EU limits; thresholds are exceeded in only 2% of the least deprived areas.

Although the distribution of indoor air quality exposures across building types and socioeconomic groups was less understood until recently, recent research studies have demonstrated that households of low socioeconomic status are exposed to higher levels of indoor air pollutants on average.^7,8 

This may be the result of overcrowding or solid fuel cooking resulting in increased particulate matter, or the use of lower quality consumer products that may emit volatile organic compounds. Lower income households may also live in lower quality housing where ventilation systems, such as extract fans, are not regularly repaired. 

This summer, the UK experienced an unprecedented 40^oC heatwave. The deadly hot spell caused more than 20,000 excess deaths across Europe. 

The effects of extreme heat can hit the most vulnerable the hardest. Older people and individuals suffering from ill health are generally found to be most at risk, but social isolation and low income can also limit one’s capacity to identify a hazard and reduce exposure. 

Poorer households may have lower thermal adaptive capacity as they may have limited access to cool spaces and be less able to afford to modify their surroundings through retrofit or use of air conditioning. 

The potential of natural ventilative cooling may be less in lower income neighbourhoods, where concerns about crime, noise and traffic-related air pollution may hinder window opening. Although fuel poverty research and policy generally refer to winter, summer fuel poverty may soon become a significant issue too. A recent CCC-commissioned report by Arup found that the cost of implementing passive cooling measures in existing homes is appreciable.⁹ 

Successfully integrating health, wellbeing and equity with net zero goals and building safety is critical towards achieving a healthy and sustainable built environment for all.

References 

1. UK Government, 2022. English Housing Survey  bit.ly/CJAprAM3
2. Keung A, Bradshaw J, 2022. Fuel poverty estimates for April 2023 following the autumn statement. Child Poverty Action Group bit.ly/CJApr23AM4
3. Middlemiss L et al. Fuel poverty in the cost of living crisis. Policy Leeds, University of Leeds bit.ly/CJApr23AM5
4. New Scientist, 2022. UK energy crisis sparks rush for firewood despite air pollution fears https://bit.ly/CJApr23FW
5. Climate Change Committee, 2022. Letter: Reducing energy demand in buildings in response to the energy price crisis bit.ly/CJApr23CCC
6. Petrou G et al, 2022. Home energy efficiency under net zero: time to monitor UK indoor air. BMJ; 377: e069435, doi: 10.1136/bmj-2021-069435 http://bit.ly/3Tr2rfe 7 
7. Ferguson L et al, 2021. Systemic inequalities in indoor air pollution exposure in London, UK. Buildings and Cities, 2(1): 425–448, doi: http://doi.org/10.5334/bc.100
8. Ferguson L et al, 2020. Exposure to indoor air pollution across socio-economic groups in high-income countries. Environment International; 143, 105748, doi: 10.1016/j.envint.2020.105748
9. Arup, 2022. Addressing overheating risk in existing UK homes. Climate Change Committee.  https://bit.ly/CJApr23OH

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Looping a rollercoaster through a building in the heat of the Arabian Desert meant maintaining a comfortable indoor temperature was fundamental to the success of the project. ‘Indoor rollercoasters of this magnitude and speed are very rare, so there were no defined environmental design criteria. Fundamentally, our approach had to be about the user experience,’ says Richard Stratton, partner and managing director Cundall MENA, the lead design consultant, with responsibility for MEP, architecture, structure and lighting.

Called The Storm, the rollercoaster features a 670m long track, coiled to fit inside a cylindrical building measuring 44.5m in diameter and 62m high. 

Designed by rollercoaster specialist Intamin, the ride lasts one minute 20 seconds. It starts with a thrilling vertical launch; in just five seconds, a linear synchronous motor propels a 12-person car from below ground to the top of the ride, 50m up. From here, gravity pulls the car earthwards, round a twisting, turning track and back to a ground-level station.

The cars are propelled 50m to the top of the ride, before gravity speeds them back down to ground level

The circular building that houses the rollercoaster is supported on a diagrid of tubular steel, a rigid structural exoskeleton. Impressively, Cundall’s engineers have designed the structure to support both the building and the rollercoaster track, so it can deal with the conventional building loads and the dynamic loads imposed by the two cars and their passengers hurtling around the track.

This diagrid is clad in a combination of triangular, composite-insulated aluminium panels and solar-controlled, vibration-isolated double-glazed panels. The glazed panels are positioned in line with the track, to give passengers views out, while the solid panels reduce solar gain. The building is capped by an insulated standing seam roof. To enhance the ride experience, the solid elements of the walls and roof incorporate an acoustic lining, helping to absorb sound.

‘There is almost 9,000m² of building envelope for the roof and the façades, which equates to a peak cooling load of about 1.35MW,’ Stratton says. 

While the building is partly shaded by the adjacent mall, in unshaded areas the fabric heat load peaks at about 300W·m², with an average heat load of approximately 155W·m²

The launch system and rollercoaster equipment add another 255kW to the total, while lighting, fresh air and people loads add a further 290kW. ‘You can see that the fabric load is the main driver for cooling, but it’s also the biggest variable because, in the evenings and during the winter, the vast majority of the load will disappear completely,’ says Stratton.

The client initially wanted to maintain the interior at 24°C, the same temperature as the mall’s retail spaces, but this would have required a significant amount of cooling. Instead, Cundall successfully argued that temperature control within the space could be relaxed, as the rollercoaster equipment is either direct liquid cooled or housed within contained equipment rooms. Examples of external rollercoasters in the United Arab Emirates that operate through peak summer conditions with only the loading/unloading areas enclosed were also highlighted. 

Stratton says: ‘Relaxing the temperature allowed us to be more creative with temperature gradients and humidity levels within the ride volume, so we could focus more on building needs to avoid condensation and large temperature variations and less on people needs’. 

Cundall MEP’s solution was to concentrate on what Stratton refers to as ‘a temperature gradient arrangement’. This sets out to maintain temperatures of 24°C in the basement, where the maintenance team is based, and at ground-floor level, where the ride is boarded. Above the occupied zone, the temperature is allowed to increase gradually, to a peak of 30°C beneath the roof.

The temperature gradient approach leant itself to a displacement ventilation solution. This would have worked ‘in principle’, says Stratton, but there was insufficient space at the base of the building because of the track, station and other ride demands.

Instead, Cundall made use of the building’s central core to house a stack of air handling units (AHUs). This non-structural element was needed by the maintenance team to access the upper levels of track, and includes a staircase and lift. The core’s six floors now house a series of double-stacked AHUs, mounted one above the other. 

Maintaining the coaster clearance zone was critical, so HVAC distribution is confined to the core. Only electrical cabling and containment was coordinated with the track and either followed the track route or was confined to designated containment routes. BIM 360 was employed throughout the design and construction to facilitate coordination and integration of the various building and track elements. 

‘If you consider the building in plan as a doughnut, the solid part contains the ride while the central section contains all the plant and equipment,’ explains Stratton, who describes the air supply system as ‘simple’. 

The supply air duct leaves each AHU and immediately wraps around three and a half sides of the core. The duct incorporates drum louvres to blow cooled air 16m from the core towards the façade, which is where the bulk of the heat is generated. ‘The drum louvres allow a bit of flexibility in where we direct the airflow and help create a bit of mixing, which is enhanced by the turbulence from the car charging through,’ says Stratton. 

Varied in capacity, the AHUs are typically between 4.5m³·s^-1 and 7m³·s^-1, based on vertical location and heat load. The overall supply air volume is 81m³·s^-1, which is sufficient to deal with the diversified load. Stratton says supply and return conditions are ‘pretty standard’; the supply is 13°C, with the return air temperature dependent on where on the building’s vertical temperature gradient unit is located. Stacking the AHUs vertically enables the system to control the rollercoaster space air temperature in horizontal slices. Variable speed drives enable the supply air volume to be increased or decreased to regulate the temperature of each slice. ‘The beauty of this solution is that you can change the setpoint of each slice to play with the temperature gradient,’ explains Stratton.

Adopting a strategy that allows the temperature gradient to rise from 24°C to 30°C at the upper levels reduced energy demand by approximately 11%. To lower energy demand further, operators could let the temperature in the upper portion of the building rise to 40°C, which, in the cooler months, would mean ‘they would probably only need to condition the lower levels’, says Stratton.

The heat-load modelling carried out to establish viability of the layered approach meant that computational fluid dynamics modelling was not needed to predict airflows. Stratton says Cundall did not worry too much about rider comfort from an air-mixing point of view. ‘The main thing was that there was a bit of air mixing and a bit of flexibility to control the direction of the air.’ 

All of the space conditioning AHUs operate on 100% recirculation. In a clever piece of coordination, the vertical AHU return air grilles are stacked adjacent to the ride’s vertical launch. The launch system is liquid cooled by packaged cooling units provided by the rollercoaster supplier. The proximity of the return air grille ensures that heat rejected by the system is sucked immediately into the AHU before it can enter the space.

At the top of the AHU stack is small fresh air supply unit. ‘Fresh air is not a big issue because there are only about 40 people inside the ride area,’ says Stratton. The unit pulls fresh air into the space from an intake on the roof, based on an allowance of 15L·s^-1 per person in rollercoaster space. Stratton says humidity is ‘managed’ by the fresh air system; ‘because this is not a close-control environment, we don’t need fine control’.

The rollercoaster building is illuminated by four kilometres of linear strip LED lighting. Cundall was responsible for designing the lighting scheme for the inside and outside of the building. Internal lighting is themed and coordinated with the ride; external lighting is focused for attraction and branding, and is customisable by the operator. ’There is a day and night experience, with the lighting designed to enhance the experience at night,’ Stratton says.

The circular building housing the rollercoaster is supported on a diagrid of tubular steel

Cooling, power and other utility services are all from the mall’s centralised energy systems. ‘All energy provisions are from the mall, so we had to ensure there was enough capacity in the district cooling, power and other utility services, such as fire protection systems.’ Fire protection, firefighting and water services all extend from the mall central systems. Cooling is from the mall district cooling system based on a peak cooling load of 1.66MW. 

Because of the magnitude of peak electrical loads, the associated operational harmonics, and compliance with local electricity regulations, a dedicated sub-station had to be constructed directly adjacent to the rollercoaster building. 

Passengers start their journey in the mall, where they buy tickets and enjoy a short audio-visual show. From here, they pass into the main building, ready to be thrilled by the ride and not by Cundall’s clever environmental control solution. ‘If people are worrying about comfort conditions, that probably means the rollercoaster is not very exciting,’ says Stratton, who knows this is not the case, having been on the ride three times already – just to make sure! 

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Since the start of the pandemic, there has been growing recognition of the importance of virus carried in exhaled breath in the transmission of SARS-CoV-2.² Virus shed in the respiratory system of an infected individual become encapsulated in droplets of respiratory fluid. 

These droplets have a continuum of sizes (and, therefore, volume of fluid) ranging
from <1μm to 100μm-plus. Once exhaled, they can decrease in size because of evaporation, and the smallest droplets (sub 5μm) – often termed aerosols – can remain airborne for hours, building up in poorly ventilated indoor spaces. 

Over time, the concentration of viable virus in the air of a room containing an infector will reach a steady state. The poorer the ventilation, the greater the steady-state concentration of virus in the air.

Are schools poorly ventilated?

The importance of ventilation in providing suitable air quality for comfort, concentration and health has long been understood. Before the early 20th century,³ the only way to provide outside air was by natural means – exploiting the natural forces to encourage outside air in and exhausting contaminated air out. This principle has remained popular for UK classrooms and most schools have a natural ventilation strategy, although mechanical and mixed-mode ventilation are becoming more popular – especially in newer schools. 

Most natural ventilation designs require the opening of a vent, usually a window, to provide a means of incoming and exhaust air. This can create issues with cold draughts in the winter and often – because of a lack of occupant understanding of the ventilation strategy – results in vents being kept shut. The resulting lack of ventilation leads to a build up of exhaled breath, bio-effluents, off-gassing pollutants from furnishings, and pathogens, leading to a less healthy environment, which has been shown to affect pupil concentration and cognitive ability.⁴ Perhaps this has led to the notion that classrooms are poorly ventilated? 

Before Covid-19, much research into school indoor air quality (IAQ) concluded that, in the main, poorly ventilated classrooms are the result of a lack of occupant interaction with the ventilation design strategy rather than a sub-optimal strategy.⁵

Often, classes noted as being poorly ventilated in winter are assessed as being well ventilated in summer, despite the design strategy remaining the same.⁶ Indeed, if we are to say that most school classrooms are poorly ventilated, it would suggest that the many architects, engineers, contractors and building control personnel involved in the design and build of schools for more than a century have failed to consider this important aspect of building design. 

As well as providing adequate IAQ, ventilation is often used to cool classrooms. Typically, the flowrates required to provide ventilative cooling are larger than the flowrates required for IAQ. As such, there should be the capacity within the ventilation design to provide adequate IAQ during the heating season.

How can we balance ventilation provision with occupant comfort? This is not a new problem. See Figure 1 for a Victorian solution for tempering incoming air. Another strategy was pre-heating incoming air and using heat sources under windows, creating a plume of hot air that mixes with incoming, cooler outside air. However, this method resulted in heat escaping out of the window.

Figure 1: Tempering incoming air was school design guidance in the 1870s. Here is an example of outside air being drawn behind the back plate of an open fire (A-B) and pre-heated before being drawn into the classroom through a decorative grille (Ref: Robert Robson)

In recent decades, there has been a drive to improve the energy efficiency of classrooms, with more airtight rooms to prevent the continuous flow of outside air through cracks. In older classrooms, these adventitious draughts have provided some background ventilation, but in newer buildings, it has become even more important to get the ventilation design strategy right.

For more than a decade, guidance for new-build schools has requested that the supply of outside air be delivered in a way that does not result in draughts. In 2018, the school ventilation design guide BB 101⁷ set out a non-statutory design framework for the delivery of outside air year round. This has led to several innovations for classroom ventilation that use heat generated in the classroom from occupants, lighting, computers, and so on to pre-warm incoming air – reducing the need for additional space heating while delivering comfortable ventilation. 

As there are many thousands of school buildings in the UK, it is inevitable that there will be some poorly ventilated classrooms. These may have arisen because of modifications to spaces, changes of use, changes to ventilation provision – for example, the addition of window-opening restrictors – or systems in need of repair. 

The provision of CO₂ monitors to schools should help them identify poorly ventilated classrooms and undertake remedial works to bring it up to standard. In those spaces where ventilation provision cannot be solved in the short term, consideration should be given to air cleaning technologies until an appropriate solution can be implemented (see CIBSE’s Air cleaning technologies).

Future classroom design

Ventilation should not be considered in isolation. If we focus building design solutions on the health and wellbeing of occupants, we must consider all aspects of design, including energy efficiency, ventilation, lighting, and acoustics (see CIBSE TM40 Health and wellbeing in building services). The golden thread of design intent of the holistic design also needs to remain unbroken from concept through to construction completion. 

The Department for Education’s Building Bulletin design guides are useful. Where guidance is non-statutory, designers should ensure clients and building users understand the benefits of adhering to the guidance notes to produce the best indoor environments for the life of the building. 

Educating occupants about how to use their building to get optimal performance from these designs will remain a challenge.  CJ

• DR Chris Iddon MCIBSE is the chair of the CIBSE Natural Ventilation Group

REFERENCES

1. England could fit Covid air filters to all classrooms for half cost of royal yacht, The Guardian, December 2021, bit.ly/CJApr22CI2.
2. Covid-19: epidemiology, virology and clinical features, UK Health Security Agency, updated 6 October.
3. Robson, ER, 1874, School architecture: being practical remarks on the planning, designing, building and furnishing of school-houses.
4. The relationships between classroom air quality and children’s performance in school, Building and Environment, April 2020, bit.ly/CJApr22CI3.
5.  IAQ in naturally-ventilated primary schools in the UK: Occupant-related factors, Building and Environment, August 2020, bit.ly/CJApr22CI4.
6. Iddon, CR, Huddleston, N, Poor indoor air quality measured in UK classrooms, increasing the risk of reduced pupil academic performance and health. In Proceedings of the International Indoor Air Conference, Hong Kong, China, 7–12 July 2014.
7. BB 101: Ventilation, thermal comfort and indoor air quality 2018, gov.uk  bit.ly/CJApr22CI5

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Located, for the most part, in London, the British film-production sector had to contend with that city’s most notable meteorological occurrence: fog. The heavy, industrial-era fogs of the Victorian period – known as ‘pea soupers’ or ‘London particulars’ – formed when moisture in supersaturated air (for example, mist) condensed on particles of largely man-made smoke, and persisted well into the 20th century. They were most problematic during the winter ‘fog season’, which lasted from November to March.

Film producers found that fog worked its way inside the studio, where it disrupted shooting. Even a light fog was visible to the camera – more so than to the human eye – and it was not unusual to lose whole days of filming, and significant amounts of money, to fog. A solution needed to be found if the industry was to remain operational all year round and compete with films made in other countries. Some producers decamped to warmer, clearer climes in the winter, with the French Riviera proving particularly popular. As one director grumbled in 1922, Britain’s winter climate meant that, for months each year, ‘British pictures can be produced abroad better than they can be in Britain’.

Technological solutions were sought that would permit production to continue closer to home. Heating the stages reduced the relative humidity of the air and prevented water vapour condensing into fog. It also had the effect of evaporating fog that entered the studio from outside.

The Whitehall studios, at Elstree, boasted an underfloor heating system − 90 pipes of 2in (50mm) diameter – which prevented fog from interrupting filming. Together with the heat given off by powerful electric lights, this could make studios extremely hot, and when Chu Chin Chow (1934) was made at Islington, some technicians worked in a state of near undress.

London’s industrial fogs also contained particles of pollution, however, that remained in the air even after the water had evaporated. These were visible to the camera, so studios were compelled to clean the air that entered, and then circulated around, their production spaces. Various solutions were proposed, including pressurising the studio environment to prevent fog ingress, and using a direct current brush discharge ioniser to ‘bring down soot particles’. This latter idea was never implemented, probably because, as one trade paper noted, such equipment was ‘not altogether without effect upon human beings… Drowsiness and nervous symptoms are believed to be sometimes brought on by it’.

More effective, and safer, were air conditioning systems, the first of which was installed at the Famous Players-Lasky studios in Islington – a location described as ‘the very worst position for fog in the whole of London’. When the studio opened in the spring of 1920, high- and low-pressure coils were installed on opposite walls of the stages to move foggy air towards the roof, where it was expelled by an exhaust fan. Initial tests found that, even when the fog could not be dispersed entirely, it could be raised to a height of 15 feet (4.5m) above the floor, allowing production to continue underneath.

The system proved unable to cope with heavy fogs, though, and 20 days were lost during the studio’s first year. Consequently, a new system was installed. Designed by W E Riley – who, as London County Council’s chief architect, had helped design the London Underground’s ventilation plant – and S L Groom, of the Carrier air conditioning company, the system consisted of an air washer that circulated up to 3.5 million cubic feet of air per hour (27.5 m³s^-1). It drew air from outside and washed it to remove airborne particulates.

The spray water was from the water company’s mains, at a temperature of around 35°F (2°C), and reduced the air to close to its dew point, 100% saturation. This cooling process removed moisture from the air, which was then reheated to prevent condensation by counterintuitively employing a spray washer. This ensured a comfortable working environment. The system was automated to maintain reasonable conditions inside the studio as weather conditions and internal loads varied.

Edna Best rehearsing a scene for Michael and Mary at Islington Studios circa 1930

In Shepherd’s Bush in 1927, the Gaumont-British studios were fitted with plant that extracted impurities from the air by means of fabric filters – a process that was developed by engineering firm Hall & Kay for use in Lancashire cotton mills. Gaumont-British had first encountered it while filming Hindle Wakes (1927) on location in Manchester. So effective was the Hall & Kay plant that the company boasted, in December 1930, that not a day of filming had been lost to fog since it had been installed.

From the early 1930s, the British film industry trade press carried fewer reports detailing the technical specifications of fog-dispersal plant, assuming that its readership was already familiar with such equipment. Continuing an earlier trend, new studios were erected outside the London ‘fog zone’ – at places such as Denham and Pinewood – and the importance of air clarity to the production of high-end productions meant these were also fitted with fog-dispersal plant.

A combination of fewer fogs, the installation of air cleaning equipment, and the construction of new studios in less fog-prone areas meant reports of disruption by fog became fewer and further between as the 1920s and 1930s progressed.

Given the efforts to which British film-makers went to keep fog out of the studio, it is ironic that numerous types of artificial fog were developed for use in the production of British films. To capture London as it actually was and as it existed in the cultural imagination (Peter Ackroyd has claimed that the London fog became ‘the world’s most famous meteorological phenomenon’), filmmakers often included fog in their production design, seeking a replacement that looked like the real thing, but that was more biddable and photogenic.

A significant number of days’ filming were lost to London pea soupers infiltrating film studios

The techniques used to create artificial fogs evolved from bonfire smoke controlled by blankets via steam and the application of filters or chemical solutions to the camera lens, to the vaporisation of diesel and increasingly sophisticated chemical fogs, with some technologies being imported from other countries. Three kinds of synthetic fog were used during the filming of Rent the luck of the sailor in 1934. Fake fog, like the meteorological phenomenon it mimicked, could also be injurious to health. Actors found that it irritated their eyes, noses and throats, while some crew resorted to wearing gas masks to counter its effects.

The fogs that plagued London into the mid-20th century became far less of a problem as a consequence of clean air legislation, suburbanisation lowering population density in the centre of the city, and electrification of houses. However, although London’s manmade fogs have now cleared, their impact on the geography and mechanical plant of film-making in Britain remains clear. As clear, in fact, as the air of the stages in which so many British films were shot.

• A longer version of this article was originally published in the Historical Journal of Film, Radio and Television bit.ly/CJFeb22RF, and thanks are due to that journal for giving permission to republish in this form.
• Richard Farmer works on the ERC-funded STUDIOTEC research project at the University of Bristol

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