Philippe Fournet-Fayard
Eolis América Latina
Expert Contributor

Biosafety: Basic Rules, HVAC specs and COVID-19 Protection

By Philippe Fournet-Fayard | Tue, 09/29/2020 - 13:30

Biosafety is a science, with theories, rules, design criteria, and operating procedures. It is largely used in the industry, at the research and development, production, and diagnostic levels. But some of its basic techniques are worth understanding at the domestic and office levels because of the COVID-19 pandemic. One of the tools that can help protect our own environment, as it is in the biosafety industry, is the HVAC. Why ventilation, how and how much air to supply, are some of the questions many people have. They are often easy to answer with common sense…

In this article, most of the basics come from well-known biosafety guidelines. These documents are the standard for designing and building biosafe areas in the industry. They are:

  • The Biosafety in Microbiological and Biomedical Laboratories, 5th edition, 2007, CDC, US Department of Health, (also known as the BMBL)
  • The Laboratory Biosafety Manual, 2004, World Health Organization
  • Guía Técnica para la Evaluación y Prevención de los Riesgos Relacionados con la Exposición a Agentes Biológicos, REAL DECRETO 664/1997, MINISTERIO DE TRABAJO Y ASUNTOS SOCIALES, España
  • Norme Canadienne sur la Biosécurité, 2015, Gouvernement du Canada
  • Lineamientos para la Gestión de Riesgo Biológico, Asociación Mexicana de Bioseguridad (AMEXBIO), 2016
  • Laboratory biorisk management, CWA 15793:2011, CEN, Europe
  • Guidelines, or even standards, in many countries, for specific applications (most of them focused on agriculture topics)

Books Covers

These guidelines are not aligned, and it is highly recommended to whom is in charge of designing a lab to study all of these.

Nevertheless, the guidelines coincide in several definitions.

One is the risk classification (as per WHO):

Classification of Infective Microorganisms by risk group
Classification of Infective Microorganisms by risk group

and its corresponding biosafety level:

Relation of risk groups to biosafety levels, practices and equipment
Relation of risk groups to biosafety levels, practices and equipment

The other one is the general philosophy of biosafety.

Biosafety is the result of the following sum of factors:

Microbiological risk assessment
Good working practices
Primary safety barrier
Secondary safety barrier
Medical survey


In a biosafety facility, the target is to protect the operator, and the general environment that is around the facility, from the microorganism that is processed.


The primary safety barrier is basically what directly protects the operator: the Personal Protection Equipment (clothing, gloves, masks, etc) , and the Working Benches (biosafety cabinets, restricted access barriers, or isolator technology). All this equipment is classified depending on the BioSafety Level of the facility (BSL) and the level of protection that has been defined during the risk assessment, as shown in the following tables (as per CDC):

Selection of safety cabinet Through Risk Assessment
Selection of safety cabinet Through Risk Assesment
Comparison of Biosafety Cabinet Characteristics
Comparison of Biosafety Cabinet Characteristics

The secondary safety barrier must protect the environment from the contamination that can be generated in the facility. It is directly linked to the design of it, its construction, and its HVAC systems. The HVAC system is defined as critical for these areas, so that it requires special attention. Associated with RAB’s equipment and the cleanroom-type of enclosure, it is responsible for creating the containment of the areas.

An HVAC system of this kind is made of supply fans, exhaust fans, filters, cooling and heating coils, humidification, and an automatic control system. In our case, several of these pieces of equipment are not the common variety.

As one of the requirements is to maintain the room in negative pressure ALWAYS, special attention will be paid to the exhaust fan and its reliability. We often see a double fan to minimize the risk of exhaust failure. Depending on the class of the BioSafety Cabinet, the BSC may have to be connected to the exhaust system; maintaining the exhaust becomes even more critical.

The supply fan, if not necessary for creating negative pressure in the room, is critical to the dilution of the contaminant. The activity of most biological agents decreases with their concentration. All the fans will have to be centrifugal, to maintain the airflow even when the filters get dirty. For the same need of dilution effect, it is not recommended to have recirculation of air in a BSL.

The filters are the other critical element. Just look at the sizes of particles we are chasing:

Human Hair Photo

They are responsible for preventing the entry of external contaminants and for keeping internal contaminants from getting out, moved by the airflow. When HEPA (High Efficiency Particle Arresting) filters are required as per the initial risk assessment and the reference guideline, the filters must be certified and tested on site (integrity and efficiency). The filters on the exhaust are mounted in a Bag In Bag Out casing. This is a casing that allows the maintenance technician to change the filters without having any direct contact with them. Sometimes, two in line HEPA filtration stages are installed on the exhaust; a failure (rupture) of the first in line does not put the environment at risk.

COVID-19 is a disease created by a virus (SARS-CoV-2, a coronavirus), with impact on the respiratory system and with a high capacity of transmission. Officially acknowledged late in the timeline of the pandemic, it also has the capacity to travel on airborne aerosols! So, the ventilation systems may have an impact, positive or negative, on the virus transmission.

To be active, the virus needs to be present with a certain concentration. Several studies show that the part of the droplets spread when we breath, talk or cough that can be an airborne transmitter is very small compared to the bigger drops that fall quite quickly down to the ground. Very few, very small airborne particles.
Then, the ventilation principles we have to apply in all closed areas are:

  • Dilution: we have to supply as much fresh air as possible and avoid recirculation of exhaust air.
  • Diffusion: the air must be supplied from the clean area to the potentially contaminated area.
  • Filtration: in case it is impossible to cancel recirculation of air in the system, it is highly recommended to add a HEPA filtration stage (and change, at least, the fan motor to maintain the airflow, which is critical for dilution)
  • In the office or at home, common sense calls for:
  • Open spaces: avoid closed areas, use balconies, terrasses, backyards as much as possible.
  • Natural ventilation: open the windows as often as possible.

Biosafety as known in the industry is here to provide indications on how to behave in the face of situations that can be a virus transmission risk. In addition to the sanitary rules that are obligatory in any epidemic situation, the correct ventilation with 100 percent fresh air in closed areas is necessary to avoid virus concentration and contamination risks. Using outside areas as much as possible is also a good measure.
We must remember that when we talk about safety, we need to deal with the cost of it. The safer we want our installation to be, the more expensive the investment will be.