2023-11-09 23:40:08
Los fires in nightclubs in Spain have caused at least 162 deaths in the last 45 years. In the last one recorded, in Murcia, 13 young people have died. And another 81 died on a sadly unforgettable night at the Alcalá 20 nightclub in Madrid in 1983.
A short circuit or a poorly extinguished cigarette sets off a spark and the clubs burn like torches, with hundreds of people trapped in a circle of fire. Inside, everything from the curtains to the sofas is made from highly flammable polymers, and the music and lights are not music and lights without electronic components, which are often the epicenter of the bonfire.
The same thing happens in our homes: rooms like the bedroom or kitchen have everything necessary to spread the flames.
Surrounded by plastics
Almost all materials used in interior decoration and furniture are highly flammable. This includes curtains, which are mainly made of fabrics of polyestersofa cushions (foam polyurethane), carpets (synthetic fibers), tables and chairs (wood and plastic), wallpaper (wood fiber/plastic), etc.
Electronic equipment, such as televisions, computers, and sound systems, also contain large amounts of flammable materials, such as thermoplastic polyurethane (TPU), ethylene vinyl acetate (EVA), polyamide, epoxy resins, polyethylene (PE) the polypropylene (PP).
Why does it burn so well?
The vast majority of these materials are synthetic polymers, what we commonly call plastics.
Their low manufacturing cost, high strength-to-weight ratio, versatility and durability make them chosen for multiple uses.
Almost all the synthetic polymers They are composed of carbon, hydrogen and oxygen atoms in long molecular chains. Those longer chains generally result in stronger materials: the more building blocks used in their manufacture, the stronger the polymer.
The bad news is that they are very volatile when exposed to high temperatures (above 250 °C), at which these long chains do not maintain their molecular stability. And the volatility makes them highly flammable.
¡Fuego!
As the material is exposed to higher temperatures, the molecular chains within the polymer begin to degrade and break down.
Free radicals begin to form, unstable structures in which the bond with the general molecular chain has been broken. Combustible gases are then released which, in the presence of sufficient oxygen, initiate the combustion.
As the material decomposes, the combustion process becomes increasingly aggressive; The material becomes increasingly volatile, releasing more combustible gases until the fire sustains itself. If left unchecked, it will quickly reach its most dangerous phase: flashover.
Flashover: when leaving may no longer be an option
Once a fire breaks out, we have 3 to 5 minutes, or even less, before the flashover. This occurs when most materials in a room or enclosed space reach their autoignition temperature, the temperature at which they will ignite spontaneously without direct contact with an external ignition source. He flashover It generally occurs at around 500 °C.
This is what happened, for example, in the nightclub fire The Station a Rhode Island earlier this year, which resulted in the deaths of 100 people. It occurred when sparks from fireworks lit inside the venue set fire to the highly flammable polyurethane foam covering the ceiling and walls of the nightclub, leading to the flashover in less than a minute.
A solution without replacing materials
The omnipresence of these materials makes it impossible to eliminate them from our lives. But we are working on a more promising and practical approach: making them less susceptible to ignition.
This is the scope of research of the Group of High Performance Polymers and Fire Retardants from the IMDEA Materials Institute.
The first line of research is aimed at neutralizing flammable gases and reducing free radicals using a flame retardant additive. As the molecular structure of the polymer breaks down releasing combustible gases, the additive releases inert non-combustible gases. These serve to dilute the concentration of oxygen and fuel in the flame zone.
We are also investigating flame retardant additives that serve to create a protective carbon layer as the polymer begins to burn. The formation of protective carbon layers, which act as a barrier to delay the flow of heat and mass, is probably the most significant condensed phase mechanism in flame retardation in polymers.
And it not only serves as a barrier to heat and mass flow, but also as a means of preserving carbon, thereby reducing its conversion into flammable volatile compounds.
A retardant that works for everything
The difficulty we encounter is that the polymers used to make a toy, a curtain or electronic cables have different flammability characteristics, so flame retardants cannot be generic.
For example in recent research on thermoplastic polyurethane (TPU)a common component in electronic cable manufacturing, the introduction of flame retardant additives equivalent to 5% of the total weight of the material resulted in immediate extinguishing after removing the external ignition source.
However, in the case of another common polymer in cable production, ethylene-vinyl acetate, we have seen that it is necessary to introduce additives equivalent to 55% of the weight of the source material. That is, 11 times more than what is required in TPU to achieve a similar result.
Another example is a flame retardant in epoxy resin. developed at the IMDEA Materials Institute. By introducing 3% less flame retardants and nanomaterials, the maximum heat release rate is reduced by more than 60% and total smoke production by more than 40%.
Why are these retardants not already used in the industry?
The first reason, surely no one is surprised, is economic. The introduction of flame retardants into polymers can increase manufacturing costs. But the main obstacle is not the price, but rather it affects the mechanical performance of the polymer.
Right now, our primary goals as fire safety researchers are to improve the performance of flame retardants and minimize the effect of these additives on the properties of the polymer itself.
We will continue to research to make our homes, offices, buildings and nightclubs safer, reducing the risk of another tragedy occurring, until we make it avoidable.
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