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What are positive and negative pressure seal checks and how are they performed?

By Jessica Barrett | Last updated: December 13, 2018
Presented by Moldex

It’s important to understand that respirators aren’t a one-size-fits-all piece of PPE. If a respirator doesn’t fit correctly, it can’t do its job properly – leaving workers vulnerable to dangerous and potentially deadly leaks.

Employees must perform a seal check after initially donning a respirator and again every time an adjustment is made to it. If an employee's seal check fails, they must either re-adjust and re-check the respirator or choose another facepiece to test for a better fit. OSHA doesn’t permit the use of respirators that can’t be seal-checked (learn about 6 Factors to Consider When Choosing a Respiratory Protection Device).

The best way to check whether you have a good seal (and thus a good fit) is to conduct positive and negative pressure checks. To get started, be sure you meet the following criteria:

  • Be clean-shaven; no stubble, sideburns, or beard that could interfere with seal
  • No jewelry or facial makeup that may interfere with face-to-facepiece seal

How To: Negative Pressure Check

To conduct a negative pressure check, follow this procedure:

  1. Don the facepiece and adjust so it’s snug but not overly tight
  2. Using the palm of your hand, block the air inlet, usually found on the sides of the facepiece
  3. Gently breathe in so the facepiece collapses slightly, and hold your breath for 10 seconds

If the facepiece remains slightly collapsed while you hold your breath, this indicates that there is no inward leakage of air and the respirator is sufficiently sealed for use.

How To: Positive Pressure Check

To conduct a positive pressure check, follow this procedure:

  1. Don the facepiece and adjust so it’s snug but not overly tight
  2. Using the palm of your hand, block the exhalation valve, usually found on the bottom of the respirator
  3. Gently try to breathe out, which should allow the facepiece to puff out slightly

If a slight amount of positive pressure is able to build up inside the facepiece without any evidence of it leaking outward, the respirator is considered satisfactory to use.


You’ve found a facepiece that offers you a good fit? Great! Be sure to check the seal sporadically throughout your workday to ensure you’re sufficiently protected at all times.

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Written by Jessica Barrett

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Jessica is a freelance writer and editor from Toronto, Canada. She specializes in creating content for nonprofits and has written for organizations working in human rights, conservation, education, and health care. She loves traveling and food, speaks Spanish, and has two dogs, one of whom she rescued while living in Mexico.

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