Working Together Again

The COVID-19 pandemic has turned our world on edge. Everyone has been affected and we are continually watching, learning, and behaving in new ways as we navigate this difficult period in history. This document outlines recommendations and our best interpretation of what will be effective in supporting the film industry in safely returning to work. This is a live document and we will be adjusting and updating it as new research becomes available.

Air Changes: Fresh Outdoor Air

Studio sound stages are large indoor production spaces with vast floor areas and high ceilings; which represents a huge volume of air commonly measured in cubic feet. Current studies suggest that the potential transmission of SARS-CoV-2 (the virus that causes COVID-19) through the air is sufficiently likely, and that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems can reduce airborne exposure1.

Risk Reduction In Sound Stages

How can we reduce the risk? There has not been enough time to develop scientifically conclusive studies as to exactly what the spread and infection potential of airborne droplets or aerosolized particles of SARS-CoV-2. However, Cool Air recommends that production companies implement an air change policy for sound stages. In order to facilitate meaningful air changes, we suggest 1 to 2 changes per hour during occupancy (ideally 4-6 air changes depending on the number of people). Simply stated, the equipment response will ensure the air inside the stage is replaced 1 to 2 times every hour with 100% filtered fresh air while people are present. This will involve a large amount of equipment moving a lot of air in a continuous manner. The air must be dropped and diffused from above, and not directed horizontally, so that the possibility of the air stream passing from one person directly into the path of another is avoided2. The equipment is located outside and provisions will need to be made to deliver the fresh air inside the studio space. This will positively pressurize the sound stage, so there will also need to be provisions to allow for the stale air to escape. We also recommend changing the air inside the sound stage (minimum of one air change) immediately following filming and again prior to filming the next day.

Conditioned Air: Cooling & Heating

Conditioned air has been mechanically cooled or heated. Through the use of cooling or heating equipment we can deliver both the air changes and the conditioned air that is required on set with the same equipment package. Depending on your application, the use of spot cooling, or heating equipment operating exclusively inside the sound stage may be needed, however it will augment and not replace the fresh air package that delivers the large volume of air changes required.

Filtration: MERV & HEPA

We will be upgrading the filters on our cooling units from MERV-8 to MERV-11 rated filters. We are making this change to allow for better particulate capture. Currently, there are no studies written that prove it will have any better effect with relation to COVID-19. Additionally, we cannot attach HEPA style filters to our cooling or heating units as they are engineered to deliver a certain amount of air at a constant volume. The extra drag imposed by HEPA filters will strain the unit physically and will greatly reduce its effectiveness. We are also offering a filter change out service that is discussed further in our Standard Operating Procedure for Film Industry Installations and Removals.

There are plenty of discussions on the use of HEPA filters in the fight against COVID-19. These filters have the ability to capture the virus (which is approximately 0.125 micron in diameter3) that causes COVID-19, but they are completely ineffective in processing the massive volume of air inside a sound stage in any measurable, and cost-effective manner. These units are effective in cleaning the air inside production offices and other small spaces, but we do not support their use in large air volume areas.

Negative Air Machines: Positive & Negative Pressure

Negative Air Machines are typically small-scale machines that are used to achieve either a negative or positive pressure inside a space. They can be used as a single unit or clustered together to collectively move more CFM. They offer the ability to filter the air as it passes through the unit either as it enters the space or leaves the space.

These portable units typically move between 1,500 and 2,200 cubic feet per minute (CFM). While that sounds like a lot, they will be completely ineffective when you are looking for significant air movement or air changes in your entire sound stage. Where do they perform well? They are ideally positioned in production offices, small air volume spaces such as dressing/hair make-up areas, and editing suites, and on Set pieces, or places where Production are gathered to work closely together.

Our large air-cooled cooling or indirect fired heating units (previously discussed and shown above) are in essence large negative air machines with the added bonus of conditioning the air. They are what we recommend once the total volume of air exceeds the ability of these small units to change the air six (6) times per hour.

Sterilization Techniques: Thermal & UV-C

Sterilization Techniques4: Two areas pertaining to sterilization that we are actively investigating are thermal remediation and the use of ultra violet light in the C bandwidth (UV-C). These two technologies offer the ability to render viruses inactive that share the same characteristic as SARS-CoV-2. UV-C sterilization is widespread in hospital applications and the technology exists that allows us to incorporate these lights into our cooling and heating equipment. Thermal remediation uses air heated to 130 oF – 160 oF in a contained space to sterilize objects and eliminate the need to treat these objects with disinfectant sprays or cloth wipes.

Thermal Remediation5: We have a large supply of film friendly custom-built heaters that can be utilized with a containment box, either an insulated plywood box built on-site by your carpentry shop, up to a modular shipping container, to facilitate thermal sterilization of objects that are not able to withstand spray disinfectants. These objects need to be able to withstand temperatures in excess of 150 oF – we are thinking hand tools, chairs, tables, wardrobe textiles and other items that are constantly handled, and will need frequent cleaning.

UV-C6: We are actively investigating the effectiveness of installing UV-C light emitting bulbs inside the air handling cabinet of our air- and water-cooled air conditioning units. Evaluating and establishing the most effective wavelength is critical in the safe use of this technology. It offers another tool in the COVID-19 battle and we endeavour to make strides in this direction in the weeks and months to come.


  1. ASHRAE. Does ASHRAE’s Guidance Agree with Guidance form WHO and CDC?
  2. COVID-19 frequently asked questions: General ventilation and air circulation.
  3. Heffernan T. Can HEPA air purifiers capture the Coronavirus?
  4. Balgeman S, Meigs B, Mohr S, Neimöller A, Spranzi P. Can HVAC systems help prevent transmission of COVID-19?
  5. Rabenau H, Cinatl J, Morgenstern B, Bauer G, Preiser W, Doerr H. Stability and inactivation of SARS coronavirus. Med Microbiol Immunol. 2005; 194: 1-6.
  6. The Optical Society, Wills S. COVID-19: Putting UV-C to work.
Cool Air Rentals Ltd.
1407 East Georgia St
Vancouver, BC V5L 2A9

Cool Air Rentals Ltd.
3816 56 Ave. NW
Edmonton, AB T6B 3R8

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