Basic Documentation

Room Pressurization Control Application Guide
Biosafety Level 1 (BL-1)
Biosafety Level 1 (BL-1) is the lowest biosafety classification and applies to biological
laboratories that need no special ventilation requirements apart from an adequate room
ventilation rate. BL-1 laboratories present a low health risk to individuals and the community.
Such laboratory rooms are only required to be separated from public areas by a closed door.
Work may take place on bench tops and without containment provisions (biological safety
cabinets). BL-1 laboratories are not specifically required to be negatively pressurized,
although most ventilation designs do incorporate negative pressurization for odor control.
Biosafety Level 1 activities may also be conducted in a general chemical laboratory. In this
case, the room ventilation must also meet the requirements for a general chemistry
laboratory.
Biosafety Level 2 (BL-2)
Biosafety Level 2 (BL-2) is the classification that applies to the largest number of
microbiological and biomedical laboratories. Although some of the substances present can
result in an infection, they may still be manipulated or processed on open benches provided
that the potential for a biological aerosol release is very low and the seriousness of a
subsequent infection is also very low. BL-2 laboratories present only a small to moderate risk
to individuals in the room and only a limited risk to the community. Such laboratories require
self-closing doors and any work where biological aerosols are likely to be released must be
done within biological safety cabinets. BL-2 laboratories are required to be negatively
pressurized to prevent airborne pathogens and aerosols from leaving the room.
Biosafety Level 3 (BL-3)
Biosafety Level 3 (BL-3) is the classification that applies to laboratory rooms that work with
highly infectious agents that are transmissible as aerosols (such as, Anthrax, Tuberculosis.
etc.) and the room ventilation requirements are stringent. BL-3 rooms must use biological
safety cabinets for all work being done in the room. These laboratory rooms must also be
separated from other building areas and have a double door (airlock) entry arrangement.
Most often, these laboratories also have adjacent areas under somewhat lesser negative
pressurization for worker gowning, showering, and other support purposes. Ventilation
system provisions for BL-3 laboratories require a single pass (no-return air) system with
HEPA
1
filtered exhaust. The room static pressure must be negative to ensure against
outward airflow. Maintaining an effective room barrier with minimal penetrations makes it
advantageous to use a dedicated room ventilation system inside the laboratory unit.
1
High Efficiency Particulate Air filter. HEPA filters are capable of entrapping biological aerosols.
6 Siemens Building Technologies, Inc.