A respirator is a specialized piece of personal protective equipment designed to protect the user from inhaling hazardous atmospheres. Its primary function is to safeguard the lungs from airborne contaminants such as dust, fumes, gases, and vapors. These devices are used across industrial, emergency, and medical settings to ensure a supply of clean, breathable air. Respirators are broadly categorized into three main types based on their protection mechanism.
Air-Purifying Respirators
Air-purifying respirators (APRs) function by actively cleaning the ambient air before it reaches the wearer’s lungs. This involves drawing the surrounding air through a filter, cartridge, or canister that traps or neutralizes contaminants. APRs are categorized based on what they filter, distinguishing between protection against solid particles and protection against gases and vapors.
Particulate filters, like the common N95 or P100 designations, physically remove aerosols and solid particles from the air stream. The numerical rating indicates the minimum filtration efficiency: N95 filters at least 95% of particles, while P100 filters capture a minimum of 99.97%, meeting the High-Efficiency Particulate Air (HEPA) standard. The letters N, R, or P denote resistance to oil, indicating if the filter is not resistant, somewhat resistant, or strongly resistant to oil-based aerosols.
Chemical cartridges operate differently, using sorbent materials like activated carbon to adsorb or absorb specific gases and vapors. These chemical filters are color-coded to indicate the type of hazard they protect against, such as organic vapors or acid gases. APRs must never be used in an atmosphere that is immediately dangerous to life or health (IDLH) or oxygen-deficient (below 19.5% oxygen).
Supplied-Air Respirators
Supplied-air respirators (SARs), also known as airline respirators, deliver clean breathing air from a source located outside the contaminated work area. This allows them to be used safely in IDLH environments and atmospheres that lack sufficient oxygen. The user is connected to this remote source, such as a compressor or a bank of high-pressure cylinders, by a long air hose.
The air delivery to the facepiece is regulated in one of two ways: continuous flow or pressure-demand. Continuous-flow SARs provide an uninterrupted stream of air, which is simpler but consumes air rapidly. Pressure-demand systems maintain a slight positive pressure within the facepiece at all times, meaning any small leak results in air flowing out rather than contaminants flowing in.
Mobility is limited by the air supply hose, which is typically restricted to a maximum of 300 feet. Because a hose failure or compressor shutdown could be catastrophic in an IDLH environment, SARs used in these conditions must incorporate a small escape air cylinder. This cylinder provides five to fifteen minutes of air for the user to reach safety.
Self-Contained Breathing Apparatus
The Self-Contained Breathing Apparatus (SCBA) is a specific type of atmosphere-supplying respirator where the entire air source is carried by the user. This system consists of a high-pressure compressed air cylinder, a pressure regulator, and a facepiece, all mounted on a carrying harness. The on-board air supply offers maximum mobility and is the preferred device for emergency entry into IDLH atmospheres, such as those encountered by firefighters.
SCBAs are classified as either open-circuit or closed-circuit systems. The common open-circuit SCBA discharges the user’s exhaled breath directly into the ambient atmosphere. In contrast, a closed-circuit SCBA, often called a rebreather, filters and recirculates the exhaled air after removing carbon dioxide and replenishing the consumed oxygen.
While open-circuit systems are standard for firefighting, closed-circuit devices are used when a longer duration of air is required, such as in mine rescue operations, providing up to four hours of breathable air. Due to the bulk and weight of the air cylinder, SCBAs are limited to a service life of 30 to 60 minutes for entry-and-escape use, making them unsuitable for long, continuous work periods.
Selection Criteria and Proper Fit
Selecting the correct respirator depends on the specific hazardous environment and the concentration of contaminants present. The Assigned Protection Factor (APF) is a numerical value representing the level of respiratory protection a given class of respirator is expected to provide. For example, a half-mask air-purifying respirator has an APF of 10, meaning the air inside the facepiece should be at least ten times cleaner than the air outside.
The APF is used to calculate the Maximum Use Concentration (MUC) by multiplying the APF by the Permissible Exposure Limit (PEL) of the hazardous substance. Full-facepiece respirators generally have a higher APF of 50. Pressure-demand SCBAs and SARs can have an APF up to 10,000, reflecting their high level of protection.
The expected level of protection is only achieved if the respirator forms a secure seal on the wearer’s face, making fit testing mandatory for all tight-fitting models. Protocols ensure the user is wearing the correct size and that no air bypasses the filter or air supply system. A qualitative fit test (QLFT) relies on the user’s ability to detect a test agent, like a bitter or sweet aerosol, to confirm the seal is intact.
A quantitative fit test (QNFT) is more precise, using an instrument to measure the actual amount of leakage around the face seal. This test produces a numerical result called a “fit factor,” with a minimum fit factor of 100 required for half-mask respirators. The presence of facial hair is a common restriction that must be addressed before a tight-fitting respirator can be used safely.