“It’s no secret,” Bengt Kjellberg said, “that when you work harder you breathe harder. The important question is whether or not the filter [used to protect the wearer against particles] and the cartridge [used to protect the wearer against gases] will protect you at your maximum respiratory demand.” Kjellberg, president of Safety Equipment America (S.E.A.), an international manufacturer of high-performance respiratory protection equipment, was referring to the filters found in negative pressure air-purifying respirators (APRs) and fan-powered air-purifying respirators (PAPRs), commonly used for hazardous materials response and cleanup.
For years, those using APRs and PAPRs focused on the ability of the filter to protect the wearer from airborne contamination. It was taken for granted that, if the wearer was able to adequately seal the mask to his/her face, and if the filter was appropriate for the anticipated airborne hazard, and if the ambient oxygen concentration was above 19.5 percent (certain other considerations for use also were factored in), the APR or PAPR would provide adequate respiratory protection.
However, there seems to have been little or no thought given to the level of work the wearer might be expected to perform, a consideration that has a direct effect on respiratory effort–which affects not only the speed at which inspired air travels through the filter but also the volume of air inspired that will be needed to support higher workloads. These are important considerations that affect the overall effectiveness of the filter.
A Dangerous Oversight?
Unfortunately, that oversight may place the uninformed wearer in jeopardy. “It is important to give first responders respiratory protection that really works,” Kjellberg also said. He made clear, though, that in saying the protection “really works” he means that it protects the wearer all the time, not just when he or she is breathing normally. “Basically,” Kjellberg said, “you must be sure your respirator will meet the demands of your peak air flows.” Regrettably, this hugely important concept is frequently overlooked when using negative-pressure APRs or PAPRs.
PIAF: Peak Inhalation Air Flow. The maximum instantaneous flow rate at which air is inhaled.
Minute Volume: The amount of air inhaled in one minute.
Constant Flow: A fixed airflow not considering the variation of airspeed during inhalation and exhalation.
A paper entitled Peak Inhalation Air Flow During an Agility Test Performed By the U.S. Marine Corps shows that test subjects consistently “out breathe” a NIOSH (National Institute of Occupational Safety and Health) – approved PAPR, with a tight fitted mask, in 97.9 percent of the measured breaths. Kjellberg is a co-author of the paper, which reflects the results of a study commissioned by the U.S. Marine Corps’ Chemical and Biological Incident Response Force (CBIRF). The CBIRF was created, well before the 9/11 terrorist attacks, to serve as a national – i.e., not strictly Marine Corps – team capable of performing as a short-notice U.S. hazardous-materials response unit anywhere in the world. If any group of first responders should be concerned about the effectiveness of respiratory protection, it would be the members of the CBIRF team.
Basically, the CBIRF report set out to determine if filter-cartridge respirators and fan powered air-purifying respirators would protect U.S. Marines in action. To make that determination, a group of 45 Marines were run through a physically demanding agility test equipped with a data-logging SE400AT respirator. The SEA400AT is a high-performance (breath-responsive) fan-powered positive pressure air-purifying respirator capable of providing positive pressure in the mask at a peak flow of up to 400 liters. The filter is designed to be effective against all known gases likely to be used in time of war, toxic industrial chemicals, biological agents, and radioactive particulates.
The test subjects (young men and women) completed an agility course while outfitted with military clothing and military boots. Among the numerous test events on the rigorous schedule were a stair climb, an equipment carry, a maze search, and other physically demanding challenges. The test lasted about 15 minutes. At the end, all of the “breathing data” – how much air was breathed, how fast, etc. – was downloaded from the masks into a computer, which calculated that approximately 6,550 breaths were taken collectively by all the users during the test.
Essentially, the study found that, 75 percent of the time, the test subjects’ average peak inhalation airflow (PIAF) during strenuous physical exertion was between 200 and 300 liters per minute. The standard NIOSH test for the effectiveness of air-purifying respirator filters and cartridges, it should be noted, is based on a constant flow rate of 85 liters per minute. PAPRs with tightly fitted masks are NIOSH-tested at a constant flow rate of 120 liters per minute, and PAPRs with loosely fitted hoods are tested at a constant flow rate of 165 liters per minute. A 1981 NFPA (National Fire Protection Association) -compliant SCBA, tested on a breathing-machine simulator, must flow at 103 liters per minute (with peak flows of approximately 300 liters) without going negative in the mask.
Essentially – and this is the crux of the issue – the CBIRF study shows that, if the wearer is exerting himself or herself while wearing a PAPR with a tight-fitting mask (or loose-fitted hood), he or she may (according to current NIOSH testing standards) be out-breathing the respiratory protection available–a possibility that is not routinely considered by the user.
Surprises and Sledgehammers
The CBIRF study also showed that many test subjects registered PIAFs in the 400 liter per minute range – with some as high as 532 liters per minute – when using a PAPR. The surprising conclusion for the Marines was that, in order to avoid a negative pressure in the mask (during exertion), the PAPR would have to accommodate airflows of 427 liters per minute for 95 percent of the Marines tested – that figure is considerably higher than common testing standards require.
Several commonly accepted peak inhalation airflow values provide yet another frame of reference: At complete rest, an adult PIAF hovers around 40-50 liters per minute. Light exertion such as walking boosts that number to 80-150 liters per minute. Running produces PIAFs of 200-250 liters per minute, and very hard work – e.g., rowing a boat – will easily produce a PIAF value well over 300 liters per minute. It seems obvious that the values probably would be significantly higher for anyone searching a collapsed building for survivors, moving heavy rubble, carrying a victim, or swinging an axe or sledgehammer. It also should be noted that none of the tests described above took speech into account – but talking while wearing a mask can increase PIAF by 50 percent.
The bottom line is obvious: Understanding the need for and availability of respiratory protection is essential for anyone working in contaminated environments. Anyone seeking additional information on respiratory protection – including technical reports on peak inhalation air flows, inward leakage tests, and ventilation volumes – is invited to visit the S.E.A. website at http://www.sea.com.au/. Then click into the Knowledge Bank to be connected to a broad spectrum of technical reports covering many important aspects of respiratory protection. In addition, a 30 March 2005 draft of the Concept for CBRN Powered, Air Purifying Respirator (PAPR) Standard can be found on the Center for Diseases Control (CDC) website.
Rob Schnepp is division chief of special operations (ret.) for Alameda County (CA) Fire Department. His incident response career spans 30 years as a special operations fire chief, incident commander, consultant, and published author. He commanded numerous large-scale emergencies for the Alameda County (CA) Fire Department, protecting 500 square miles and two national laboratories in the East Bay of the San Francisco Bay Area. He twice planned and directed Red Command at Urban Shield, the largest Homeland Security exercise in the United States. He served on the curriculum development team and instructed Special Operations Program Management at the U.S. Fire Administration’s National Fire Academy. He is the author of “Hazardous Materials: Awareness and Operations.” He has developed risk assessment, incident management, and incident command training for Fortune 500 companies, foreign governments, and U.S. national laboratories.