A respirator is a device engineered to safeguard the wearer from inhaling hazardous atmospheres, including particulate matter (dust and aerosols) and invisible gases and vapors. These devices operate by creating a barrier and providing clean, breathable air to the wearer’s respiratory system. The fundamental way a respirator delivers this clean air dictates its design, application, and limitations.
The Fundamental Divide: Air-Purifying Versus Atmosphere-Supplying
Respirators are broadly categorized into two classes based on how they source the air the wearer breathes. Air-Purifying Respirators function by actively removing contaminants from the ambient air surrounding the wearer. These devices use filters, cartridges, or canisters to clean the inhaled air before it reaches the lungs.
The second category, Atmosphere-Supplying Respirators, provides a clean, independent source of breathing air. This air is delivered to the facepiece from a remote location or a self-contained source. Air-Purifying Respirators can only be used when the atmosphere contains sufficient oxygen and when the hazard concentration is known and below established limits.
Atmosphere-Supplying Respirators are designed for use in environments where the air is immediately dangerous to life or health (IDLH) or where oxygen levels are deficient. Since they do not rely on filtering the surrounding air, they offer the highest level of protection against unknown or highly concentrated hazards.
Air-Purifying Respirators: Filtering Ambient Air
The most commonly encountered type of respirator is the filtering facepiece, often seen as a disposable mask covering the nose and mouth. These function on a negative pressure principle: the wearer’s inhalation creates a slight vacuum that draws contaminated air through the filter media. A tight fit to the face is necessary for these devices to force all inhaled air through the filter and prevent leakage.
Elastomeric respirators offer increased reusability and protection, featuring a durable half or full facepiece made from rubber or silicone. These devices utilize replaceable cartridges or canisters that screw directly onto the facepiece, allowing components to be swapped based on the specific hazard. Particulate filters capture airborne solids and aerosols, while chemical cartridges contain sorbent materials like activated charcoal to trap gases and vapors.
Powered Air-Purifying Respirators (PAPR) use a battery-operated blower, unlike negative pressure types. The motor pulls ambient air through the filter and pushes it into the hood, helmet, or tight-fitting facepiece. This constant flow creates a positive pressure inside the facepiece, which makes breathing easier and protects against inward leakage of contaminants. This mechanism is beneficial for individuals who have difficulty breathing through negative-pressure filters or who require a less restrictive seal.
Atmosphere-Supplying Respirators: Providing Clean Air
The Self-Contained Breathing Apparatus (SCBA) uses a portable tank of compressed air carried on the wearer’s back. The air cylinder provides a limited but independent supply of breathable air, making the SCBA the preferred choice for environments such as firefighting or rescue operations in IDLH conditions. Operational duration ranges from 30 to 60 minutes, depending on cylinder size and air consumption rate.
The Supplied-Air Respirator (SAR), or airline respirator, connects the wearer to a remote source of clean air via a long hose. The air source is usually a compressor located safely outside the hazardous area, allowing for continuous, long-duration use. This design is frequently used for activities like abrasive blasting, painting, or welding in confined spaces.
The primary limitation of the SAR is that the wearer is tethered to the air source by the hose, restricting movement and travel distance. This category also includes specialized Emergency Escape Respirators. These are miniature, self-contained units designed exclusively for short-term use, providing just enough air for the wearer to quickly exit a contaminated or oxygen-deficient area.
Understanding Filtration Ratings and Regulatory Standards
The performance of air-purifying respirators is standardized by regulatory bodies, such as the National Institute for Occupational Safety and Health (NIOSH) in the United States. This system uses a combination of letters and numbers to indicate the filter’s resistance to oil and its efficiency level. This classification dictates what airborne hazards the filter can handle.
The letter designation specifies resistance to oil aerosols, which can degrade the filter’s effectiveness. The three classifications are N, R, and P. The letter is followed by a number that indicates the minimum filtration efficiency.
The three classifications for oil resistance are:
- N-Series: Not resistant to oil; used only in environments free of oil-based aerosols.
- R-Series: Resistant to oil; provides protection for up to eight hours if oil is present.
- P-Series: Oil Proof; used when oil aerosols are present for extended periods.
The three efficiency ratings are 95, 99, and 100, corresponding to the percentage of airborne particles the filter is certified to capture. For example, an N95 filter captures at least 95 percent of airborne particles, while a P100 filter captures at least 99.97 percent of particles and is oil-proof. This standardized rating system allows users to select the level of protection needed for known contaminants.