An N95 or P100 filters particles such as wildfire smoke, dust and ash, while a respirator fitted with gas cartridges or canisters also removes the specific gases and vapours named on its label. None of them filters carbon monoxide, supplies oxygen or blocks gamma radiation, so the right choice depends on whether the hazard is a particle or a gas.
Most confusion about masks comes from one missed distinction. Some hazards are particles: tiny solids or droplets floating in the air. Others are gases and vapours, which are individual molecules mixed into the air itself. A filter that is excellent at one can do nothing at all for the other.
This guide sets out what each type of respirator does, where each one stops working, and the three things no consumer mask does.
Particles and gases are different problems
Particulate filters work like a very fine mat of fibres. An N95 is a NIOSH class that filters at least 95% of airborne particles. A P100 filters at least 99.97% and also resists oil. Both catch the fine particles in wildfire smoke, dust, ash and mould spores.
Gas molecules pass straight through that mat. NIOSH is direct about it: "these respirators only filter out particles. They do not protect against gases or vapors, and they do not provide oxygen."
To remove a gas you need a sorbent, usually treated activated carbon, packed into a cartridge or canister. Each sorbent is made for particular families of gas, and the label lists them. A cartridge that is not rated for a gas should be assumed to do nothing for it.
What each type stops
| Type | Stops | Does not stop | Typical use |
|---|---|---|---|
| N95 disposable respirator | At least 95% of airborne particles when it seals to the face | Any gas or vapour, carbon monoxide, lack of oxygen | Wildfire smoke particles, dust, ash, clean-up work |
| P100 filters on a reusable half mask | At least 99.97% of airborne particles, with a better seal than most disposables | Any gas or vapour, carbon monoxide, lack of oxygen. No eye protection | Repeated or longer use in smoke, dust or mould |
| Half mask with organic-vapour and acid-gas cartridges plus P100 | Particles, organic vapours and the acid gases named on the cartridge label | Carbon monoxide, gases not on the label, lack of oxygen, unknown or very high concentrations. No eye protection | Solvent and paint vapours, some chemical odours, smoke particles |
| Full-face mask with combination gas and particle canisters | Particles and the gas types printed on the canister, with eye and face coverage | Carbon monoxide, lack of oxygen, gamma radiation | Irritating gases and particles where eyes also need protection |
Two notes on the last row. The words "gas mask" describe a shape, and approvals vary. In North America, NIOSH approves a CBRN respirator as a complete system: one specific facepiece with one specific canister. In Europe, facepieces are certified to EN 136 and filters are marked by gas type, such as A for organic vapours, B for inorganic gases, E for acid gases and K for ammonia. Both routes are legitimate, and they are separate claims.
Our own full-face respirator kit is certified to the European standards and is not NIOSH CBRN approved. If a seller claims a NIOSH approval, you can check it against the NIOSH Certified Equipment List, which is linked in the sources below.
Wildfire smoke: what a respirator can and cannot do
Wildfire smoke is a mix of fine particles and gases. The fine particles are the part a respirator can reduce. Health Canada says a well-fitting, properly worn NIOSH-certified N95 or equivalent respirator, such as a KN95 or KF94, can reduce exposure to the fine particles in wildfire smoke. The same guidance says it does not protect against the gases in smoke.
A respirator is for the time you have to be outside. On a smoky day, the more useful measures are usually staying indoors with windows closed and running a suitable air cleaner. Our wildfire smoke guide covers the whole plan.
Disposable respirators also age. Manufacturers set the shelf life, commonly five years, and a respirator past its date is no longer considered NIOSH-approved. Check the date on the box when you put masks into storage.
Three things no mask does
No mask is a radiation mask
Nothing you can wear on your face stops gamma radiation. A particulate filter can reduce how much radioactive dust you breathe in, and that is all it does. Reducing exposure from outside the body takes dense material and distance, which means being indoors.
The Government of Canada's advice for a nuclear emergency is to go inside, stay inside and stay tuned, and to be prepared to shelter in place for at least 24 hours. See our nuclear emergency guide and our article on potassium iodide pills.
No N95, P100 or standard canister filters carbon monoxide
Carbon monoxide passes through particulate filters, and it is not removed by organic-vapour cartridges or by standard CBRN and ABEK canisters. That is why none of the respirators in this article is a house-fire escape device. Health Canada notes that carbon monoxide has no smell, taste or colour, so you will not notice it through a mask either.
No filter supplies oxygen
Every product here is an air-purifying respirator. It cleans the air that is already present. In a space with too little oxygen, or with a gas at an unknown or very high concentration, a filter will not help. Those situations call for supplied air and trained responders, and the right action for everyone else is to leave.
Fit, beards and glasses
A respirator only works if air goes through the filter and not around it. That makes fit the deciding factor for every type in the table.
- Facial hair: a tight-fitting respirator does not seal over a beard or stubble. This applies to disposable N95s, half masks and full-face masks alike.
- Size: faces vary. Try the model you plan to rely on before you need it, and choose a different size or shape if you feel air leaking at the edges.
- Seal check: follow the manufacturer's seal-check instructions each time you put the mask on.
- Glasses: ordinary glasses break the seal of a full-face mask. Most need a prescription insert.
- Workplaces: occupational use requires formal fit testing. Home use has no such rule, but the physics are the same.
Children
NIOSH approves respirators for workplace use, and they are designed for adult faces. NIOSH says children aged two and over can wear respirators, but that small sizes "may not have been tested for broad use in children." Health Canada's wildfire guidance says respirators are not for children under two.
Child-size KN95 and KF94 masks exist, but they are not NIOSH-approved, and a poor fit on a small face is common. For children, plan around cleaner indoor air and less time outside first, and treat a mask as a secondary measure.
Which one to keep at home
This part is our judgement, not an official recommendation. For most Canadian households the realistic airborne hazard is wildfire smoke, and a box of NIOSH-approved N95s such as our smoke pack covers it. A reusable half mask makes sense if you do dusty or solvent-heavy work, or expect to be outside in smoke for days.
A full-face mask with canisters is a specialised item. It covers a narrower set of situations than its appearance suggests, and it needs a clean-shaven face, the right size and filters that are in date. If you buy one, read the canister label and treat that list as the full extent of what it does.
Frequently asked questions
Does an N95 protect against wildfire smoke?
A well-fitting NIOSH-approved N95 reduces the fine particles you breathe in wildfire smoke, which Health Canada identifies as something a respirator can help with. It does not filter the gases in smoke, including carbon monoxide, and it does not supply oxygen. It works only when it seals to the face, so facial hair and a poor fit reduce the benefit.
Is there a mask that protects against radiation?
No. Nothing worn on the face stops gamma radiation. A particulate filter such as an N95 or P100 can only reduce the amount of radioactive dust you inhale. In a nuclear emergency the official advice is to go inside, stay inside and stay tuned.
Will a gas mask protect me from carbon monoxide in a fire?
No. Standard gas mask canisters, organic-vapour cartridges, N95s and P100 filters do not remove carbon monoxide, and none of them supplies oxygen. A working carbon monoxide alarm and leaving the building are what protect you.
Sources
- NIOSH: wildfire smoke and respirators (2025 bulletin)
- Health Canada: using a respirator mask during wildfire smoke events
- NIOSH Certified Equipment List
- NIOSH: CBRN air-purifying respirator standard
- Health Canada: carbon monoxide
- Government of Canada: how to prepare for a nuclear emergency
General information only. Follow instructions from local emergency officials, and call 911 in a life-threatening emergency.