Article Archive
Eye Strain
Research shows certain temperature and heat conditions can seriously damage face piece lenses on standard firefighter breathing equipment
Vol. 27 Spring 2012

It is an image gruesome enough for any Freddy Krueger movie poster. The close-up apparently shows a firefighter in a helmet and bunker gear wearing a heat damaged SCBA face mask, the plastic that was once molten having reformed like hardened lava.

Where the firefighters’ left eye should be, a hole has melted through the lens piece. Fortunately, what stares back resembles a doll’s eye – a pressure sensor. The “firefighter” is a polyurethane head outfitted with sensors to monitor heat flow during testing by the National Institute of Standards and Technology (NIST).

The results? Researchers uncovered that temperature and heat-flow conditions can seriously damage facepiece lenses on standard firefighter breathing equipment, a potential contributing factor for fire-responder fatalities and injuries. The findings are detailed in a report sponsored by the U.S. Fire Administration and the Department of Homeland Security.

That report is now under review by the National Fire Protection Association’s Technical Committee on Respiratory Protection Equipment, said committee chairman Dan Rossos with Portland (OR) Fire & Rescue.

“Anytime something like this happens we try to jump on it immediately to figure out what is going on,” Rossos said. “Sometime you have a unique set of circumstances or a chain of events that no one can anticipate.”

Significant changes have already been proposed for NFPA 1981, the standard covering open circuit self-contained breathing apparatus (SCBA) for emergency services, addressing two key testing components, Rossos said.

The next edition of the standard is being prepared for issuance in 2013.

“We realized in our research that we are not dealing with the same fire world we were dealing with 25 or 30 years ago,” he said. “We need to address it in new ways.”

Supporting the proposed change is evidence from six separate incidents and eight fatalities in which thermal degradation of SCBA face mask lenses were likely a factor in the circumstances surrounding the fatalities, said Stephen Miles, a safety and occupational health specialist with National Institute for Occupational Safety and Health (NIOSH).

“We are excited that we can increase the safety of SCBA, but we are quick to point out that the modern certified SCBAs of today are doing a good job day in and day out,” Miles said. “Are there mass issues of thermal degradation of lens? Not that I’m aware of.”

 

BASIC  ISSUE

The basic issue identified by NIOSH investigations is whether the face piece lens melted while the fire fighters were still on air or did the damage happen after the firefighter suffered smoke inhalation and asphyxiation, he said.

“If you have a firefighter perish in a fire, the victim might have extensive thermal trauma (that occurred after the fire fighter died but before their body was recovered) in addition to smoke inhalation and respiratory burns. Our investigations concentrated on whether the fire fighter ran out of air first and died from smoke inhalation or did the respiratory system suffer thermal trauma with a corresponding melting of the SCBA facepiece. This forced us to look deeper into the cause of death and obtain more information from the medical examiner and/or autopsy.

The six incidents investigated by NIOSH involved 8 firefighters known to have been using SCBA when overcome by a rapidly growing fire event.

“None of these cases except one was in a normal fire environment,” Miles said. “These firefighters were actually trying to escape from an extreme condition known as a flash over that exceeded the performance expectations of the SCBA.” Many of these fire fighters were also close to an escape point in the structure.

The exception among those fatalities was a Pennsylvania instructor stoking a building fire for trainees.

“When we looked at the SCBA face pieces used by the rest of the instructor cadre, we found that all had received repeated severe service exposures,” Miles said. “We asked NIST to try to replicate the conditions. We wanted to know what would lead to a point where the mask would degrade.”

The NFPA Technical Committee on Respiratory Protection Equipment was also anxious for more data, Rossos said.

“Anytime something like this happens we try to jump on it immediately,” he said. “We wanted to look at any standard changes that could have manifested itself in this kind of result.”

Four separate tests involving furnished townhouses in the Chicago area were conducted. Conditions for each were nearly identical save for the placement of the polyurethane head and controlled variations in fire exposure conditions, adjusted, for example, by opening and closing doors and windows as specified times.

Researchers equipped the rooms with devices to record temperatures rapidly at regular intervals between ceiling and floor. Five models of SCBA face pieces, each from a different manufacturer. A gauge to measure heat flow, or flux, was positioned next to the face pieces.

In all cases of lens degradation, the damage was due to temperatures and heat fluxes that exceeded performance limits of polycarbonate, the lens material commonly used in SCBA, Miles said.

“With exposure after exposure, the masks were in all different states of being bubbled,” he said.

 

MELTING  RATES

Overcoming the established melting rates of polycarbonate may prove difficult for manufacturers to achieve, Miles said. While that melting rate has stayed the same for many decades, the environment in which the SCBA is expected to perform has changed radically.

“The rate of heat release of modern furnishings and building is significantly higher than the rate of heat release in legacy environments,” Miles said. “UL has done a number of studies. They have a video showing two identical rooms, one filled with legacy furnishings and one with modern furnishings.”

It took 26 minutes for the legacy environment to flash over. The environment with modern furnishings flashed over in less than four minutes.                    è

“It’s all about heat flux and the rate of heat release,” Miles said. “Take a birthday cake with one candle burning on it. That candle is burning at 1,100 degrees Fahrenheit. Now take the same cake and put 100 candles on it the candles are still burning at 1100 or so degrees Fahrenheit, butyou can’t put your face anywhere near it. The heat release rate is much higher.”

New products incorporated into carpeting, floors, wall covering and furnishings use petroleum based synthetics that create a higher temperature in a shorter period, Rossos said.

“As we started to work with NIST to replicate what we were seeing in the field, what we started realizing is that to get what we were having happen required a significant combination of convecting and radiating heat at levels we had not seen before,” he said.

Of course, the thermal protection from personal protective equipment has vastly improved during the same period. Unfortunately, that may have contributed to today’s face piece issue.

“I’ve been a firefighter for nearly 30 years,” Rossos said. “When I first came aboard we did not wear hoods. The thermal protection from our turnouts only reached a certain mark. The types of heat and temperatures impacting the lens would have been intolerable then. Long before we had physical degradation we would have bailed out.”

New testing with regard to thermal degradation is proposed for the next edition of NFPA 1981, he said.

“The SCBA must meet a basic convection test of 500 degrees Fahrenheit for five minutes,” Rossos said. “Then there will be a 10 second direct flame impact on the SCBA. The SCBA has to maintain 80 percent of its volume for certain time periods. It’s a destructive last-ditch survivability test. The SCBA is thrown away once this testing is done.”

More specifically, the lens surface will be hit with heat amounting to 15 kilowatts per meter square for a specific period. Again, pass-fail for the SCBA is determined by maintaining 80 percent of its volume.

However, concentrating on more stringent standards rather than training that better teaches firefighters the limit of their PPE may simply move the next problem to a different part of the ensemble, Rossos said.

 

MAJOR  CHANGES

 Major changes to the thermal performance requirements have been proposed for the 2013 edition of NFPA 1981, Rossos said.

“My fear, as I’ve stated before is that these changes alone will not solve the problem without the understanding that this fire world we live in today is much different than that of 25-30 years ago contributing to increased heat and reduced time. These factors combined with the thermal protective advancements made available in our PPE have in my opinion possibly reduced our sensory ability to determine what environments we can safely work in. If we fail to recognize these factors and incorporate them into our SOPs, behavior and disciplines, my fear is that we will continue to find the next weak link in our PPE.”           

 
 

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