A respirator is a personal protective device that filters or supplies clean air to protect you from breathing in harmful particles, gases, or vapors. Unlike a loose-fitting surgical mask, a respirator is designed to form a seal around your nose and mouth so that nearly all the air you inhale passes through the filter material. Respirators range from lightweight disposable models like the familiar N95 to heavy-duty systems that supply air from a separate tank.
How a Respirator Filters Air
Respirator filters don’t work like a simple net that catches anything bigger than its holes. They rely on several physical mechanisms working together, which is why they can trap particles far smaller than the gaps between their fibers.
Large particles (roughly 1 micrometer and above) get caught through inertial impaction. They’re too heavy to follow the airstream as it curves around a fiber, so they slam into the fiber and stick. Mid-sized particles, down to about 0.6 micrometers, get caught by interception: they follow the airstream closely enough that they brush against a fiber as they pass. The smallest particles, below 0.2 micrometers, are captured through diffusion. These ultrafine particles bounce around randomly (a behavior called Brownian motion), and that erratic path increases their chance of colliding with a fiber.
On top of all this, many respirator filters use electrostatic attraction. The fibers carry an electric charge that pulls particles toward them, which is especially important for capturing tiny particles that might otherwise slip through gaps. This electrostatic layer is one reason respirator filters perform far better than a simple cloth barrier of the same thickness.
Respirators vs. Surgical Masks
The critical difference is the seal. A surgical mask is a loose-fitting, disposable barrier. Its edges are not designed to form a seal around your face, so unfiltered air leaks in around the sides with every breath. A respirator, by contrast, is engineered for a very close facial fit. The edges press against your skin to force incoming air through the filter material rather than around it. That seal is what makes a respirator genuinely protective for the wearer, not just for the people around them.
Two Main Categories
Every respirator falls into one of two broad categories based on how it delivers clean air.
Air-Purifying Respirators
These pull surrounding air through a filter, cartridge, or canister to remove contaminants before you inhale. The types include:
- Filtering facepiece respirators (like the N95): disposable masks where the entire facepiece is the filter material.
- Elastomeric respirators: reusable rubber or silicone facepieces with replaceable filter cartridges. These come in half-mask versions that cover the nose and mouth, and full-facepiece versions that also protect the eyes.
- Powered air-purifying respirators (PAPRs): a battery-powered blower pushes air through a filter and into a hood or facepiece, so you don’t have to pull air through the filter with your own breathing effort.
Atmosphere-Supplying Respirators
These deliver clean air from an independent source rather than filtering the surrounding air. They’re necessary in environments where contaminant levels are too high for a filter, or where there isn’t enough oxygen. The most recognizable example is the self-contained breathing apparatus (SCBA) that firefighters wear, which carries a tank of compressed air on the user’s back. Supplied-air respirators connect to a remote air source through a hose instead.
Understanding the N95 Rating
The name “N95” encodes two pieces of information. The letter tells you about oil resistance, and the number tells you filtration efficiency.
The letter designation breaks down like this:
- N: not oil-resistant. Use only where oil-based aerosols are absent.
- R: somewhat oil-resistant, but only rated for a single shift (8 hours).
- P: oil-proof, with longer-term use allowed per the manufacturer’s guidelines.
The number, 95, means it filters at least 95% of airborne particles at 0.3 micrometers, the particle size that is hardest to catch. Particles both larger and smaller than 0.3 micrometers are actually captured more efficiently, so 95% represents the worst-case performance. Respirators rated 99 or 100 filter at least 99% and 99.97%, respectively.
International Equivalents
Different countries have their own certification standards, but several are roughly comparable. In Europe, the EN 149 standard defines three classes: FFP1 filters at least 80% of 0.3-micrometer particles, FFP2 filters at least 94%, and FFP3 filters at least 99%. An FFP2 is approximately equivalent to an N95. China’s KN95 standard similarly requires 95% filtration. These aren’t perfectly interchangeable because testing protocols differ slightly, but they target similar levels of protection.
Protection Factor Ratings
OSHA assigns each respirator type an Assigned Protection Factor (APF), a number that tells you how much the respirator reduces your exposure. A half-mask air-purifying respirator (including N95s) has an APF of 10, meaning it reduces airborne contaminant concentration to one-tenth. A full-facepiece air-purifying respirator has an APF of 50. A powered air-purifying respirator with a full facepiece can reach an APF of 1,000, reducing exposure to one-thousandth of the ambient level.
These numbers guide workplace respirator selection. If the contaminant level is 20 times the safe exposure limit, a half-mask respirator (APF of 10) isn’t sufficient, and you’d need at least a full-facepiece model.
Fit Testing and Why It Matters
A respirator only works as well as its seal. OSHA requires anyone using a tight-fitting respirator in the workplace to pass a fit test before use, repeated annually and any time you switch to a different brand, model, or size. Weight changes and dental work can also alter your face shape enough to break a previously good seal.
There are two types of fit tests. A qualitative test is pass/fail: a sweet or bitter test agent is sprayed near the respirator, and if you can taste or smell it, the seal has failed. A quantitative test uses an instrument to measure exactly how much air is leaking past the seal while you perform movements like bending, talking, and turning your head. Loose-fitting respirators, like hooded PAPRs, skip fit testing entirely because they don’t rely on a facial seal.
Filter Replacement and Maintenance
For reusable respirators with replaceable cartridges, knowing when to swap a filter is essential. You cannot rely on smell alone to tell you a cartridge is spent. OSHA requires employers to establish a written change schedule based on the specific chemicals, concentrations, and working conditions involved.
Several factors shorten a cartridge’s useful life. Breathing harder (from heavy physical work) pulls contaminants through faster, cutting service life proportionally. High humidity above 85% can reduce cartridge life by half. Temperature matters too: every 10°C rise can reduce service life by 1 to 10%, depending on the chemical. As a rough guideline for organic vapor cartridges, a chemical with a boiling point above 70°C at a concentration below 200 ppm gives about 8 hours of protection at a normal work rate. Cutting the concentration by a factor of 10 extends that life roughly fivefold.
Particulate filters (the kind used for dust, smoke, or biological aerosols) are generally replaced when breathing through them becomes noticeably harder, which signals the filter is loaded with trapped particles. For disposable filtering facepiece respirators like N95s, replacement is straightforward: discard the entire unit when it becomes damaged, visibly soiled, or difficult to breathe through.