Safe Work Australia updates ventilation advice

Comments

1. Peter Small

   November 27, 2021

   Under the heading of “Mechanical Ventilation” in its advice, echoed by AIRAH in paragraph 5 of the HVACRNEWS article, SWA states “Air purifiers or cleaners such as those fitted with high-efficiency particulate air (HEPA) filters can lower the concentration of airborne contaminants (including viruses) in the air..” .
   But in “Table 2: Measures to improve mechanical ventilation” immediately below that section in the advice, SWA appears to be narrower in its guidance, mandating that ONLY air purifiers that utilise a HEPA filter should be used for ventilation improvement..i.e. “Use only HEPA filters. Air cleaners that use other types of filters are less efficient are less effective than those with HEPA filters at reducing the concentration of COVID-19 virus in the air”.
   Excusing that the last sentence doesn’t quite make sense (at least to me), I don’t know why SWA advice would go beyond the UK, US and WHO advice from which it adapted. In addition, I believe the generalisation is incorrect. I can provide an example of an air purifier technology readily available in Australia that disproves that statement. I would think that SWA would be aware of that too.
   SWA’s warnings in both sections that machines are to be operated and maintained “as per the manufacturer’s instructions”, presumably refers to the issues of reducing performance of the filter as it becomes saturated, and to the safety precautions for maintenance that reflect the reality that the physical membrane captures microbes but does not necessarily neutralise them.
   I would think the latter is set to become an even bigger issue than it is currently, when more infectious new COVID variants inevitably arrive, and should be worthy of consideration in developing risk assessments and control measures in accordance with an employers’ obligations if they are responsible for the maintenance of the machines. Also, surely technologies that are proven to eliminate microbes, reducing this danger, such as the one I mention, would also be worth considering rather than simply an air purifier with a HEPA filter in it.

   Reply
   1. David Metcalf

      March 12, 2022

      The fixation with HEPA only, defies evidence. It’s often ideal, if the system supports it, and you’re trying to prevent all transmission between two already separated spaces. But there’s other applications. ASHRAE’s Taskforce recommends MERV-13 or better (the best supported if possible). Plus there’s a reason that DIY filters like CR Boxes, using MERV-13, are so extremely popular with dozens of professors of aerosol science, HVAC engineering, etc. Appropriately sized logarithmic decay works for in-room recirculating filtration.

      Reply
2. John Healey

   November 29, 2021

   The poor level of technical discussion of Mechanical Services Systems is again reflected in this article and PARTICULARLY in the linked article from Safe Work Australia. https://covid19.swa.gov.au/doc/improving-ventilation-indoor-workplaces-covid-19#
   With COVID19 the transmission of disease occurs when the airflow moves fine vapour droplets from an infected person to a target person.
   Increasing or decreasing outside air percentages, CO2 levels, opening windows have no impact on this. In fact opening a window may increase a cross-draught that moves COVID19 vapour droplets to a victim/target, increasing risk.
   These articles contain the usual naive belief systems that “more outside air is good” and then attempt to relate that to COVID19. Yes, the BCA/NCC contains target CO2 levels for outside air design and these appear reasonable for odour (eg: BO) and contaminant control (eg: VOCs) by implication, but have NOTHING to do with COVID19 risk.
   The articles look like they have been written by a well-intentioned intern following instructions from a Public Service clerk. This is not engineering.

   John Healey: (No 4891)

   Reply
   1. David Metcalf

      March 12, 2022

      Unfortunately, John Healey and Chris Musgrave, a significant part of your statement (perhaps the most significant), is disproven by epidemiological evidence, bioaerosol physics, and empirical studies of emissions.

      Specifically: “Increasing or decreasing outside air percentages, CO2 levels, opening windows have no impact on this.”.

      That would rely too much on the large ballistic droplet theory (dogma) of viral respiratory disease transmission. It’s been espoused by charlatans like Prof. Peter ‘Open Air Factor’ Collignon. But reality is, those things do usually work.

      While SARS-CoV-2 doesn’t behave exactly like cigarette smoke (it lacks the VOC gas components, etc., of course); it certainly does behave significantly like that. The old hazy smokers’ rooms that you used to see in some airports, is a fair approximation to most indoor spaces today.

      SARS doesn’t just neatly and safely fall to the floor quickly in the absence of rapid dilution or filtration. While air flows do matter and neither is it just an idealized well-mixed uniform gas; neither does it generally remain undispersed in a room for too long without filling the space. Yes, concentrated multiphase turbulent expiratory gas clouds are a factor and short range aerosols can dominate transmission. But not to the level that it generally negates the controls like air purifiers, etc., recommended. The majority of virion concentration released is in the 1-3μm range (definitely small enough for rapid dispersal), while even up to 100μm muco-salivory respiratory aerosols can remain suspended.

      While there are edge cases, typically, increasing outside air percentages certainly will dilute infectious aerosol concentration and reduce risk.

      CO2 levels, while not the entire story, in the absence of air filtration are typically well correlated with exhaled air and generally indicative of the fractions of potentially infectious air being re-breathed by others. It can be thrown off by indoor plants, indoor cooking, fermentation, etc., and gaseous CO2 does disperse a bit faster than liquid water based aerosols. But along with PM1 readings, it’s still a very useful (if imperfect) proxy for infection risk.

      Likewise, there’s specific instances where opening windows can increase risk. E.g Introducing thermal stack effects on multi-stories, or with wind pressure differentials across building faces can overwhelm controlled mechanical ventilation (in non-compartmentalised designs), and drive contaminated air up/across into other tenancies (even through electrical/plumbing service ducting, etc.). But In the general case, more fresh air ventilation typically does decrease risk. Plus, sometimes those flows are still happening to a degree anyway, just with less dilution.

      Overall, the SafeWork Australia advice is enormous progress on what’s gone before from Australian Government. Better than most of the private sector too.

      While it’s far too oversimplified for quarantine facilities and infectious disease wards (that need highly controlled flows for near zero risk targets), as mainstream advice, where nuance doesn’t carry well anyway, it’s certainly not bad. Plus they still recommend seeking expertise anyway (which covers assessing specific circumstances and individual environment needs).

      There’s parts I disagree with too. E.g., HEPA isn’t the only option for all circumstances. In fact, due to higher flow rates from less resistance, many MERV-13 can outperform HEPA for continuous in-room recirculation (if appropriately sized), due to logarithmic decay and faster initial drop, from higher volume CADR. More turnover, means more filter passes, sooner.

      Reality is, if government had just spent $50 per household on a 20″ box fans and pairs of MERV-13 panels (at volume EOS pricing), and threw in some N95 respirators, instead of the HUNDREDS OF BILLIONS of dollars on other stimulus; then COVID would’ve been over long ago.

      Have you seen this?
      https://www.covidisairborne.org/home

      Reply
3. chris musgrave

   December 2, 2021

   I agree totally with John Healeys observations and would go on to add that we need to consider air flows in each situation to achieve something resembling operating theatre type installations where the air flow is directed upwards or downwards and not towards other persons .
   This will be particularly important in meeting rooms /Training Rooms and Classrooms where the occupancy period is short but with high occupancy levels .
   The installation of ceiling sweep fans in class rooms and operation in the Winter mode will create a situation where the air flow is drawn up to the ceiling and then down the walls or windows -giving the air born particles an opportunity to adhere to a surface instead of being inhaled by adjacent persons .
   This would be a simple retrofit and would still work in conjunction with evaporative or refrigerated a/c systems -which could also have decent filters fitted for air cleaning .

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