Establishing Shot: Team of Firefighters in Safety Uniform and Helmets Extinguishing a Wildland Fire, Moving Along a Smoked Out Forest to Battle Dangerous Ecological Emergency. Cinematic Footage.
Firefighters’ protective clothing degrades over time and new research now shows why, pointing the way toward making a dangerous job safer.
The high-performance fibres used to make the clothing are designed to offer superior mechanical performance and to withstand extreme conditions, including heat and water, while still being light and flexible enough to be comfortably worn during heavy exertion. But previous studies showed some firefighters’ protective clothing used less than the recommended 10 years did not meet the minimum strength and water repellent requirements for new garments.
Even more worryingly, in some cases damaged fabric still looks relatively unaged and there are not enough visual clues to indicate it’s no longer protective, says Patricia Dolez, an associate professor and materials engineer at the University of Alberta.
Dolez conducted some of the original research into the degradation of protective textiles in the mid to late 2000s. While her studies showed some of these fabrics degraded faster than expected, for example when exposed to humid environments, it wasn’t until she teamed up with textile engineer Saiful Hoque, who earned his PhD at the University of Alberta, that they figured out exactly why.
“There was a huge gap in the research,” says Hoque. “There are only a handful of studies about the mechanism, but none that simulated different water types and temperatures.”
In a study published in March in the Journal of Polymer Science, the pair showed how some protective fibres break down when exposed to warm water, illustrating what can happen during real-life firefighting and laundering.
Warm water laundering is necessary to remove cancer-causing chemicals from fires that accumulate on the clothing. The current standard for washing frequency is twice a year, but mounting concerns about exposure to fire chemicals means fire departments are now considering laundering after every exposure.
To simulate water exposure and laundering, Hoque immersed eight different fabrics containing 15 different yarns in both purified neutral pH and acidic water for up to 1,200 hours. Each fabric soaked at four different temperatures – 40°C, 60°C, 80°C and 90°C.
Then he used a mechanical test frame to check for signs of physical deterioration. For chemical deterioration, Hoque used spectroscopy.
While he found no chemical deterioration, physical damage was significant. The warmer the water, the greater the breakdown. In particular, fabric blends containing a type of commonly used fibre, called para aramid/polybenzimidazole (PBI) degraded in strength 68 per cent more quickly when exposed to moisture, as opposed to similar fire-protective blended fabrics that didn’t contain PBI.
Firefighters’ outer jackets and pants often include PBI fibres because they are particularly flexible and can withstand extreme temperatures. But in order to resist heat shrinkage, manufacturers treat the PBI fibres with sulfuric acid.
Dolez’s earlier research showed that traces of sulfur remain in the PBI-containing fabric. It turns out this chemical residue makes the water acidic, which causes the fabric’s tensile strength to severely degrade. To be more specific, it degrades the protective fibres’ crystallinity, which reflects the degree of structural order of a solid, and hence its tensile strength.
Omar Cherkaoui, a chemist with the École Supérieure des Industries du Textile et de l’Habillement in Morocco, called the study’s methodology “robust.” While Cherkaoui was not involved in the study, he was an arm’s examiner on Hoque’s PhD exam.
“The implications are significant for the production and use of these materials,” he said. “Further research to optimize manufacturing processes and ensure the quality and durability of final products would be beneficial.”
The pair hope their findings will help manufacturers of high-performance fibres and protective fabrics improve their processes. One solution would be to remove the sulfur residue from the PBI fibre, or use some other method of treating the fibre to resist heat shrinkage.
Dolez has contacts among manufacturers of protective clothing and has shared the study’s results with them. “We’ve pointed out the problem. Now it’s time for a collaborative effort from all stakeholders to come up with solutions and address this issue,” says Hoque.