Articles by Matthew Bishop
Our world is filled with ‘extrusions’. They are small and not-so-small cross-sections that operate as seals, bridging the complex components of machines and moving parts together and helping them to keep them in working order. There are many different types of extrusions, and the diversity of their functionality often puts them at risk of — and makes them important in preventing — situations that can lead to electrical fires. Extrusions are also often made out of different materials, the quality of which can also influence how protected an environment is against the risks of fire. The benefits of silicone One of the more well-suited materials that help with fire prevention is silicone. Silicone is a manmade compound that repels water, is electrically insulating, extremely resistant to high temperatures and, importantly, can be formulated to be a flame-retardant. These qualities and more are, increasingly, making silicone the material of choice for extrusions in manufacturing, at least in part because of these advantages. The While there is certainly more work to be done on the safety front — no environment can be too safe, after allonly other rubber with the highest tolerance for extreme temperatures is viton, but this type of material is at its best when exposed to types of fuel. In other (most) situations, silicone is arguably of superior quality. Heat-resistant or flame-retardant? There are two different types of silicone extrusions that are often confused when talking about fire safety: silicone extrusions that are heat-resistant and those that are flame-retardant. The former is manufactured to function and maintain its mechanical properties at high temperatures. A silicone extrusion operating as an oven door seal would be an example of a heat-resistant type of extrusion. The highest temperature these grades of silicone can withstand is about 300°C. Flame-retardant silicone is formulated specifically to be self-extinguishing. To be certified as flame retardant the material is subjected to a flame for a specified time. The material then has to pass a minimum burn distance, or extinguish in a certain time. Flame-retardant silicones cannot withstand the same temperature extremes as heat-resistant silicones, but have much better self-extinguishing properties in general. They tend to max out at around 200°C. When talking about fire safety, it is the grades that are specially flame-retardant that are important to think about. Although silicone is naturally heat-resistant, it is only heat-resistant up to a point. Special grades are required for the extrusions needed to function in high-temperature areas, like the aforementioned oven door. But this does not make them the same as being flame-retardant. Industry grades of flame-retardant silicone There are several grades of silicone that meet different flame-retardant requirements for specific industries. Including: UL-94: This grade is the general standard in the United States, and is most commonly specified on lighting fixtures and other components. EN45545-2: This grade is the standard in the railway industry, and to a lesser degree across all mass transit vehicles (such as buses). All silicone components used on trains, for example, need to meet this required standard. FAR/JAR 25.823: This is the flame-retardant standard for silicone components used in aircraft industries. Apart from being self-extinguishing, the other main property of flame-retardant silicone grades is that they have a low smoke, low toxicity quality. Meaning that if they do come into contact with a fire, and are subsequently burned, they will not release large amounts of smoke or toxic fumes. Low smoke, low toxicity rubbers have been a legal requirement ever since the tragic Kings Cross Station fire in 1987. In which smoke from burning rubber and When talking about fire safety, it is the grades that are specially flame-retardant that are important to think aboutother materials contributed to fatalities. As implied by the above standards, flame-retardant silicones are commonly found across the aerospace industries, the automotive and rail (and to a wider extension the mass transit) industries, and the consumer goods and lighting manufacturing bases. They are also present in the emergency services sector; usually in vehicles, including in ambulances and fire fighting vehicles. Why are fire-retardant extrusions important? An increasing trend for office spaces and everyday household items is for them to rely more and more on synthetic carbon-based polymers in the form of furniture, fabrics, housings for electrical equipment and as surface coatings for other materials, to name a few. The high fuel values of carbon-based polymers means that their very existence is potentially hazardous in the event of a fire. By having fire-retardant silicone extrusions bridging the components together in machinery and moving parts, their substance reduces the likelihood of a fire breaking out within one of these machines and spreading onwards — and causing catastrophic damage to — the everyday carbon-based polymers in the environment. An increasing trend for office spaces and everyday household items is for them to rely more and more on synthetic carbon-based polymersImportantly, the flame-retardant silicone grades used in extrusions are not harmful to human health, and in any case, exposure to them is minimal. Although some can be in visible areas, such as door seals on trains, by nature most of them are located inside machinery, and do not tend to be out in the open. Fire prevention and the future Silicone might be one of the best materials for extrusions to be manufactured out of, in terms of guarding against and preventing fire hazards. But when it comes to preventing tragedies such as the aforementioned Kings Cross Station incident, nothing can be too perfect. That’s why the standards for silicone are continuously being revised and improved upon. All the time, silicone grades are increasingly put to the test in laboratory settings and tweaked to increase their performance. The standard priorities are: how can we make this material even more likely to help with the reduction and the spread of fires? How can the amount of smoke and fumes emitted in the event of burning be even more diminished? But while there is certainly more work to be done on the safety front — no environment can be too safe, after all — the fact remains that, of all the options currently available, the safest options out there are made from silicone.