A Supplied Air Respirator (SAR), also known as an airline respirator, is a breathing apparatus that provides clean air from a source independent of the user’s immediate surroundings. It delivers breathable air through a hose from a safe, uncontaminated location, unlike Air-Purifying Respirators (APRs) that only filter ambient air. SARs are designed for environments that are highly toxic, lack sufficient oxygen, or contain unknown contaminants that standard filters cannot manage, ensuring a continuous and reliable air supply.
Core Mechanism and Essential Components
The functionality of a SAR relies on three essential components that deliver high-quality breathing air. The air source is the origin of the clean air, typically a bank of high-pressure cylinders or a specialized air compressor located in a clean-air zone. This source must meet stringent Grade D breathing air specifications, which mandate oxygen content between 19.5% and 23.5% and strict limits for carbon monoxide and condensed hydrocarbons.
Connecting the source to the user is the air supply hose, a durable line that provides the breathing air. This hose can extend up to a maximum approved length of 300 feet, which limits user mobility. The hose connects to the third main component, the facepiece or hood, which interfaces directly with the user. The facepiece can be a tight-fitting full or half-mask or a loose-fitting hood or helmet, depending on the required protection factor.
The air is regulated to ensure a comfortable and safe flow rate, sometimes with mechanisms to cool or heat the air before it reaches the wearer. This atmosphere-supplying design allows for extended work periods in hazardous conditions without the risk of filter exhaustion or breakthrough from high contaminant concentrations.
Environments Requiring Supplied Air
SARs are mandated for use in environments where atmospheric hazards pose a threat to life and health. A primary application is in oxygen-deficient atmospheres, where oxygen concentration falls below 19.5% by volume. Since APRs require a minimum level of oxygen to function, they are ineffective in these conditions.
SARs are also required for atmospheres that are Immediately Dangerous to Life or Health (IDLH)—conditions that could cause death, permanent health effects, or prevent escape. These units are necessary when contaminant levels exceed the Maximum Use Concentration (MUC) of air-purifying respirators, meaning the concentration is too high for a filter to provide adequate protection. While SARs are generally approved for non-IDLH environments, their use is extended to IDLH conditions when they are equipped with an auxiliary escape air supply.
Common work activities necessitating a SAR include abrasive blasting, paint spraying involving volatile organic compounds, and work inside tanks or confined spaces. In these settings, high contaminant levels or oxygen displacement make an external air source the only safe option. Air quality must be continuously monitored to assure the system is supplying safe air throughout the operation.
Different Types of SAR Configurations
The delivery method determines the specific configuration of the SAR, with two main operational types: Continuous Flow and Pressure Demand. The Continuous Flow SAR provides a constant stream of air to the facepiece or hood, regardless of the user’s breathing cycle. This system is often used with loose-fitting headgear, which allows air to escape around the edges, making it suitable for less hazardous environments.
A Pressure Demand SAR maintains a slight positive pressure inside the tight-fitting facepiece at all times. Air is supplied on demand as the user inhales, but the positive pressure ensures that if the face seal is compromised, air flows outward rather than allowing contaminants to leak inward. This feature provides a higher level of respiratory protection compared to the continuous flow design.
Auxiliary configurations enhance safety, such as combination units that integrate a SAR with a small, emergency Self-Contained Breathing Apparatus (SCBA) cylinder. This escape bottle provides a short duration of air, typically a few minutes, allowing the user to exit the contaminated area if the main air supply fails. These combination systems are the only SAR types approved for entry into IDLH atmospheres, provided the escape cylinder is sufficient for the travel time out.