Solution to the rescue of firefighters

Sometimes, the only thing that separates a firefighter from mortal danger is their outfit, the uniform that is supposed to protect them from flames. However, the research published over the recent years challenges the assumption that the protection provided to firefighters is adequate and sufficient (you can read about it here). Reports suggest that the increased incidence of cancer in the group of firefighters is due not only to the frequent exposure to smoke and fumes of burning materials or chemicals, but also to the carcinogenic materials used during the manufacture of their uniforms.

Dr Piotr Szewczyk aims to develop fireproof unwoven fabrics which, even when damaged or in direct contact with flames, will not emit substances harmful to human health. Owing to his project concerning refractory electrospun nonwoven fabrics of high mechanical durability, Dr Szewczyk received funding within the MINIATURA 8 call for applications by the National Science Centre.

Harmful protection

Commercially available suits for use in the high-risk sector often contain the so-called PFASs, or per- and polyfluoroalkyl substances, which in certain forms are harmless and resistant to high temperatures. The latest research, however, convinces us that, as a result of damage to their structure, they begin to secrete harmful substances that can adversely affect human health and, in particular, contribute to the formation of cancers. Similarly to Teflon – an undamaged frying pan coating is inert and cannot negatively affect our health, but when scratched it begins to release carcinogenic compounds, and so too can a damaged firefighter's suit. PFASs will begin to release and affect human health in negative ways. Unfortunately, such damage during rescue operations is not uncommon. According to the current state of knowledge, firefighter uniforms may contribute to the epidemic of cancer in firefighters.

The nonwoven fabric that Dr Szewczyk is working on is to consist of fibres coated with nanoparticles, which will provide the polymers with protection against combustion and eliminate the problem of the release of harmful substances.

The AGH University researcher intends to produce nonwovens using electrospinning. It is a technique that allows nonwovens to be obtained from polymers to which different molecules can be added at the production stage. The work starts with the preparation of a solution – the polymer, from which the fibre is to be made, is dissolved in a specific solvent. This solution is then introduced into a syringe, which is mounted in a pump. From there, the solution goes into a nozzle, which is usually a needle. The key point is that this nozzle is at a high voltage, of the order of tens of kilovolts, and there is a collector several centimetres away. This creates a very strong electrostatic field between the needle and the collector, which starts to pull out the polymer stream, and it starts to deposit on the collector, usually a metallic cylinder. The polymer stream is so thin that all the solvent that is in the solution evaporates before it reaches the collector.

The challenge is that the molecules that are supposed to form the top, fire-resistant layer of the fibre cannot mix with the polymer, they should wrap around it and form a kind of buffer zone instead. 

Power in the ashes

Nanoparticles of soot have the properties required to cover the fibres. Soot is created by combustion. It consists of the most basic carbon compounds which are inert and non-flammable. What was supposed to burn has already burned out, so we are dealing with an effect resistant to the process. What is more, large amounts of soot are created as a waste material in the oil and gas industry, so finding new ways to manage it is highly useful. Similar compounds may be created from burnt coffee beans. There is no shortage of them in the world, and they would serve as more than a product to be composted. Nanoparticles of soot can be obtained simply by grinding the microparticles in a mortar into finer fractions or using more sophisticated ball mills.

The smaller the particles, the tighter they will be able to surround the polymer and the more effective they will cut off the access of oxygen, thus a fireproof barrier is formed. Moreover, the presence of said nanoparticles increase the durability of polymer fibres (which are durable themselves). Yet another advantage of soot. The polymer chains become entangled with nanoparticles that collect stresses, which allows for higher loads to be carried.

Ceramic nanoparticles could also be used to create such a layer, but although it is a frequently used and effective method, it is also very expensive. Also, it requires the use of harmful chemicals, such as concentrated trifluoroacetic acids, so the use of soot appears more environmentally friendly and safer.

The fibres created in the electrospinning process are very thin. To the naked eye their appearance can be compared to that of a handkerchief, but their durability is many times greater. For comparison: microfibres are fibres with a diameter of less than 10 microns and nanofibres are less than a micron in diameter. Those studied by Dr Szewczyk have a diameter of 700-800 nanometres, so 10 times less. The thinner the fibre, the more useful it gets.

The uniforms that are currently popular are very thick and restrict the firefighter's movements to a large extent, getting in the way. At present, we lack technology which would provide freedom of movement and adequate insulation, as it is most easily achieved through thick layers of material. Electrospun nonwovens can be used to coat virtually any type of material with virtually no increase in volume. The fireproof membrane that the AGH University scientist is working on would not constitute the entire outfit, but only one layer, effectively protecting against the impact of flames. Thus, it would give an opportunity for the firemen and firewomen to have more freedom.