How To Make Sure Your Gas Mask Fits

How To Make Sure Your Gas Mask Fits

How To Make Sure Your Gas Mask Fits

This guide courtesy of our friends over at Mira Safety. Check out their masks, they have the best civilians can buy.

Gas Mask Fitting

The proper functioning of your gas mask relies entirely on a snug and airtight fit.

The gas mask must make a vacuum seal, meaning it must be the proper size and a good fit for the shape of your face. See the negative pressure test below. 

Medium-size masks are a good choice for many people, but a good fit is not guaranteed, so check your measurements first. If you have any questions, reach out to the folks at Mira Safety directly. They have awesome customer service

You can find the measurements for all MIRA Safety masks in the product listings on our website. 

You must try the mask on ahead of time to be sure it will work when you need it. 

You absolutely MUST shave any facial hair before using a mask. Beards and sideburns can potentially prevent forming a proper seal and compromise function.

(Editors note: brutal for us bearded dudes out there, but it is what it is. Keep a buzzer in your gas mask kit I guess? 

Proper Donning & Doffing Your Gas Mask

  1. Make sure the straps are completely loosened and pulled to the front of the mask, where they won’t get in your way.
  2. Place your chin in the chin cup and roll the mask onto your face from the chin up. Make sure your nose is in the nose cup. You may need to seat the mask a few times to get the right fit.
  3. Holding the mask in place, pull the straps into place on the back of your head.
  4. Tighten each strap securely, in the following order: middle strap, top straps, and then bottom straps.
  5. Cover the filters with your hands and inhale deeply and quickly to test the seal. This is a negative pressure test. You should feel the mask tighten around your face and no air should enter the mask. If this doesn’t happen, repeat steps 1–4.


This is the most important basic safety check for gas mask users.

You need to do this every time you put on your mask, and it’s doubly important for younger family members.

The negative pressure test involves donning your mask, tightening the straps, and then fully covering the inhalation port (if you don’t have a filter screwed in) or the inlet on the gas mask filter (if you do have a filter on the mask). Have the wearer take a deep breath in with the port covered to ensure no air can enter.

Gas mask pressure test

(Image source: MSA Europe)

The mask should suction to the user’s face, and they should feel a small amount of pressure inside it. That means the mask is correctly sealed around their face and can protect them from airborne threats. If the mask retains its shape and the pressure inside doesn’t increase, there’s an air leak.

This is especially important for kids because they grow fast. So they’ll need a gas mask that fits comfortably and isn’t too small, but it simply must pass the negative pressure test.

Especially as smaller kids grow, you’ll want to take out the gas mask and have them test it at least once a year. Since every kid is different, there’s not a universal recommendation. Some kids will be large enough to wear an adult mask before their teens, while others might require smaller masks into adulthood.

Please note, that the negative pressure test only applies to a traditional style gas mask where the seal forms around the face and not for hood-style respirators.

As long as you’re aware of which mask your kids need for practical protection, you’re in good shape.

For More Information

If you are looking to learn more about how gas masks work, what kinds are available, or really anything at all about respirators and CBRN masks - check out our Ultimate Gas Mask Guide

Bug Out Bag Builder Ultimate Gas Mask Guide

Printer Friendly, PDF & Email