When the laboratory works with biosafety level (BSL) III pathogens: create a negative pressure laboratory


Some laboratory tests for tuberculosis detection and multidrug resistance detection have a high risk of generating aerosols. These tests need to be performed in a biosafety cabinet and a containment laboratory. In phase 1 the risk level of each laboratory room was determined based on the type of tests being performed in those laboratory rooms. This was done using the WHO TB Laboratory Biosafety Manual. In chapter 1, page 12 and 13 the classification system for TB laboratories is explained. When your laboratory houses a class III laboratory room (i.e. tests are being performed that generate aerosols as described in the WHO TB Laboratory Biosafety Manual), then a negative pressure system needs to be installed in that room and the room needs to be transformed into a high-containment TB laboratory.


  • A negative pressure system is a system that ventilates air out of the laboratory (minimum 6 air changes per hour). This air passes through a HEPA filter that prevents that microorganisms are spread outside the laboratory.
  • Besides this system, an indicator also needs to be installed next to each entrance door that shows the air pressure difference in the laboratory and outside the laboratory. The air pressure difference should lie between -12.5 Pa or -0.05" w.g. (= inches water gauge) at each barrier door and the laboratory.
  • A third adaptation that should be made to the laboratory is the installation of an air lock after the entrance door to the BSL III laboratory room. In this room staff can change into/out of their dedicated BSL III lab coats and wash their hands.
  • Ensure restricted access into the laboratory room so that only authorized persons are able to access the laboratory room. For methods, see the activity on preventing unauthorized access in phase 2.

How & who

Laboratory manager:

  1. Identify funding for financing the negative air pressure system and the constructions that need to be made to the laboratory room.
  2. Plan and construct the air lock in the laboratory.
  3. Purchase and install the negative air pressure system including the pressure meters outside the laboratory room.
  4. Include the air pressure system in the preventive equipment maintenance program developed in phase 2.

Biosafety Officer:

  1. Write an SOP for Working in the BSL III Laboratory. Do this following the protocol for writing Procedure SOPs in the Master SOP and use the template for a Procedure SOP attached to the Master SOP.
  2. Review and authorize the SOP following the procedure in the SOP for Document Control.
  3. Include the SOP in the Read and Understand List and indicate which staff members have to read the SOP.
  4. Present the SOP in a weekly staff meeting and indicate which persons have to read the SOP. Explain that they must sign the Read and Understand List after reading the SOP.

NOTE that the negative pressure system must be connected to a backup electricity source to ensure that it keeps functioning during a power failure.

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This activity belongs to the QSE Facilities & Safety


ISO15189:2007: 5.2.1 5.2.2 5.2.4 5.2.6
ISO15189:2012: 5.2.1 5.2.2 5.2.6
ISO15190:2003: 6.16.2