How should a negative pressure monitor be used in asbestos work?

• A. To calibrate respirators.
• B. To measure humidity.
• C. To verify that the containment area remains under negative pressure relative to adjacent spaces.
• D. To measure air temperature.

Answer: (C)

A negative pressure monitor is used to verify that the containment area stays under negative pressure compared to adjacent spaces. This keeps airflow directed into the containment, so asbestos fibers don’t leak into surrounding areas. To use it, place the monitor at the boundary between the containment and the outside space (often near a door or seal) and read the differential pressure. You should see a negative value, indicating the containment is at lower pressure. Regular checks should occur at the start of work, after changes to ventilation or doors, and whenever the boundary conditions might shift. If the reading moves toward zero or becomes positive, inspect and fix doors, gaskets, and seals, and adjust ventilation to restore the negative pressure before proceeding.

This tool isn’t meant for calibrating respirators or measuring humidity or temperature; those tasks use other instruments.