A positive pressure respirator (PPR) is personal protective equipment designed to shield the wearer from airborne hazards. This device operates by maintaining the air pressure inside the facepiece at a level greater than the surrounding atmospheric pressure. This pressure differential ensures that any air movement across the seal is directed outward, preventing contaminants from entering the breathing zone. PPRs are used in environments where the concentration of harmful substances is high or the toxicity presents an extreme risk to health, offering superior protection compared to standard air-purifying masks.
How Positive Pressure Is Maintained
Maintaining positive pressure relies on constantly supplying clean air to the mask at a controlled rate. This air supply creates a continuous outward flow, which maintains the necessary internal pressure. One common method is the continuous-flow system, which pushes a steady stream of air into the facepiece regardless of the wearer’s breathing pattern. This constant delivery rate is designed to exceed the maximum air volume a person inhales, ensuring the pressure never drops below ambient levels.
The pressure-demand system is primarily used in self-contained breathing apparatus. This system employs a regulator that senses when the pressure inside the mask falls due to inhalation or a leak. The regulator instantly releases a burst of air into the facepiece to restore the positive pressure balance. Both continuous-flow and pressure-demand mechanisms manage air volume and pressure regulation differently but achieve the same goal of outward airflow.
The Safety Difference
The safety advantage of positive pressure over a negative pressure respirator, such as an N95 mask, lies in how it handles a compromised seal. In a negative pressure mask, inhalation draws air through the filter, creating lower pressure inside. If a leak develops, this negative pressure sucks contaminated air directly into the mask, bypassing the filter and exposing the user to the hazard.
Conversely, the positive pressure system creates an air barrier that works against inward leakage. If the facepiece seal is broken, the higher internal pressure forces a stream of clean air out of the mask and past the gap. This outward flow physically blocks contaminants from infiltrating the breathing space. This higher level of protection is reflected in a much greater Assigned Protection Factor (APF), with some positive pressure systems achieving an APF of 1,000, compared to a full-face negative pressure respirator’s APF of 50.
Different Systems Employing Positive Pressure
Positive pressure technology is integrated into two main categories of respiratory devices, differing based on their air source. The first category includes Powered Air-Purifying Respirators (PAPR). These use a battery-operated blower to draw ambient air into a filtration unit. A fan then pushes this filtered air through a hose and into the wearer’s hood, helmet, or mask, creating the continuous positive flow.
The second category involves atmosphere-supplying respirators, which deliver air from an independent source rather than filtering the surrounding air. This includes Supplied Air Respirators (SAR) and Self-Contained Breathing Apparatus (SCBA).
Supplied Air Respirators (SAR)
SARs use a long hose to connect the user to a remote, clean air source, such as a compressor or air tank located outside the hazardous area.
Self-Contained Breathing Apparatus (SCBA)
SCBAs, which are often used by firefighters, carry the entire air supply in a tank worn on the user’s back, providing complete mobility independent of external connections.
When Positive Pressure Is Necessary
Positive pressure respirators are mandated in specific environments where the risk to life is immediate and severe. These devices are required when working in atmospheres classified as Immediately Dangerous to Life or Health (IDLH). This classification includes any environment where a worker could be exposed to a lack of oxygen, high concentrations of toxic gas, or conditions that could cause death or irreversible health effects.
Scenarios requiring this protection include entry into confined spaces, remediation of hazardous chemical spills, or any situation where the contaminant type or concentration is unknown. Because the positive pressure mechanism is effective at preventing inward leakage, it is the only acceptable form of respiratory protection in these extremely hazardous settings. Supplying a non-filtered air source from a tank or remote location is necessary when the ambient air cannot be safely filtered, such as in oxygen-deficient environments.