Ventilation of isolation rooms

Between commercial and industrial ventilation

The purpose of an isolation room is to prevent contamination in the workplace by constructing a new room (or by adapting an existing space) and equipping it with adequate ventilation to ensure safe preventive isolation of contaminated or presumably contaminated personnel. It is important that exchanges between the isolation room and the outside are carried out safely, which means preventing the virus from escaping through openings such as doors and in evacuated air.

Designing and operating an isolation room carries a much greater performance obligation than is involved in regular commercial ventilation systems, known as HVAC (heating, ventilation and air conditioning). Although they are relatively simple, the ventilation systems of isolation rooms much more closely resemble industrial ventilation systems (e.g. process ventilation) than commercial systems. In addition to performance, which must be reliable and verifiable, all aspects relating to maintenance and upkeep, including the balancing and changing of filters, must be taken into consideration at the design stage, so as to minimize the risks of contaminating the various actors.

The negative-pressure ventilation concept: substantial airflow

To prevent the spread of airborne contaminants, sufficient negative pressure must be maintained in the room to block “fugitive emissions” (leaks) into adjacent spaces, such as corridors and rooms, particularly through the opening of doors as persons enter and leave the isolation room.

The airflow required to maintain sufficient negative pressure is established using either of the two following principles:

• Maintain a negative pressure of at least 2.5 pascals [0.01 inch water column] between the isolation room and adjacent premises.
• Maintain a minimum speed of air flowing into the room through openings, regardless of conditions (e.g. open door).

Once determined, this airflow must be supplied by one of the existing ventilation systems (see concrete example/step 1) or by a new system (see concrete example/step 2). Note that the calculated airflow will often be very high, representing a relatively substantial expense both on purchase and in operation. This will also present considerable challenges in selecting ventilation equipment, designing the duct networks and fitting out the site. As an example, maintaining sufficient negative pressure in a room in which a standard-sized entrance door is opened requires a flow of fresh air of 2.1 m³/s or 4500 CFM, which is 15 times higher than that required of an ordinary HVAC system. [2]

Strategies are of course proposed by BBA to reduce the required airflow while maintaining effective control of contaminants issued and present in the isolation room.

It is important to note that the air exchange rate or minimum number of air changes per hour, as required by occupational health and safety regulations, [3] must be provided by the system used to ventilate the isolation room. However, the stipulated airflow is very often lower than the values which are necessary to ensure adequate depressurization of the room. In the example used above, the airflow required to maintain the prescribed negative pressure is equivalent to more than 20 air changes per hour.

Operation, maintenance and performance monitoring

Ventilation of an isolation room must make it possible to contain airborne microorganisms (contaminants), such as aerosols and fine droplets produced by a person when speaking, coughing or sneezing. Design and operation of the ventilation system must therefore observe the criteria normally observed for cleanrooms, and must include in particular:

• Negative ventilation of the isolation room, with adequate diffusion and without recirculation (100% fresh air)
• Design of a weatherproof outside fresh-air intake equipped with adequate filtration and positioned sufficiently far from possible sources of contamination (e.g. sanitary vents).
• Appropriate management of exhaust air, including its filtration and evacuation into the environment after atmospheric dispersion.
• Supervision of aeraulic conditions, if deemed necessary; note that smoke tracing could be done as an efficiency check of the control and performance of a ventilation system.
• Electrical supply connected to the emergency circuit for all ventilation equipment (e.g. evacuation fan, fresh air unit/main unit) and control systems, if deemed pertinent.
• Scrupulous planning of inspection and maintenance work.

Concrete example

In a pandemic situation like that of COVID-19, businesses must quickly create an isolation room in a context of limited labour, accessibility and equipment availability. In the example presented here, two steps are proposed: the first is emergency conversion of an existing room in the plant, while the second is finalization of work to create a permanent, safe, standards-compliant facility.

Step 1: Converting an existing room into an isolation room (short-term mitigation)

Although the concepts applicable to providing ventilation for an isolation room can be followed, the design criteria cannot. Once the flows of fresh air and evacuation have been calculated, it is important to determine the capacity of existing ventilation systems and formulate a usage strategy. However, it must be understood that if the gap between the required performance and that of the existing ventilation systems is too great, new equipment will be required. Temporarily fitting out an existing room has the following pros and cons:

• Pros: quick setup and low costs.
• Cons: limited efficiency, depending on the circumstances, and limited duration, depending on the owner’s agreement.

Step 2: Setting up a new isolation room (permanent solution)

The second step includes preliminary design, detail engineering, and installation of a new ventilation system that will meet all prescribed requirements. In addition to airflows (which must be sufficient) and functioning of the system (which must be reliable, so redundancy may be required), the fresh-air intake must be positioned judiciously, and exhaust air must be dealt with adequately. Permanent installation of an isolation room has the following pros and cons:

• Pros: satisfactory efficiency and performance that meet applicable legal requirements.
• Cons: high implementation and operating costs.

Our multidisciplinary team’s advanced expertise in industrial ventilation and HVAC will allow you to take informed decisions about setting up and operating isolation rooms, whether they be new or installed in existing premises.

At BBA, we design durable, high-added-value industrial ventilation systems, thanks to our in-depth knowledge of capture, purification, pumping and piping systems, as well as our expertise in materials handling and power management. With the BBA team, you will be able to make informed choices that will help you comply fully with current standards and optimize your operating costs.

[1] WORKPLACE SANITARY STANDARDS GUIDE – COVID‑19: Exclusion from the Workplace (isolation of workers).

[2] The reference room used for this example is a 93 m² [1000 sq. ft.] pharmacy laboratory occupied by 10 persons, requiring a flow of new (fresh) air of 0.11 m³/s [230 CFM] under ASHRAE standard 62.1-2019.

[3] For example, under section 103 of the Regulation respecting occupational health and safety (ROHS, CNESST Québec),