It seems the electric revolution is finally here. According to the International Energy Agency, there were more than ten million electric cars on the world's roads already at the end of 2020 – up 43% from 2019. By the end of this decade, the total number of electric cars, buses, vans, and trucks is projected to jump to 145 million or possibly even 230 million if enough countries tighten their emission targets. Carmakers are investing billions to secure their slice of the market. One of the challenges they face in building mass-market electric vehicles (EVs) is fire safety. But probably not in the way most people think.
Contrary to what action movies would have you believe, cars rarely burst into flames. If they ever do catch fire, passengers usually have more than enough time to walk away safely. That is why fire safety regulations for cars are a lot less strict than for planes, trains, or even most electronics used in homes. But now, with the advent of EVs, news reports of burning EVs have caused new concerns.
Are electric cars at risk?
According to the US National Fire Protection Association (NFPA), electrical failures are already one of the leading causes for fires in conventional cars, accounting for one in four vehicle fires in the United States. With EVs carrying high energy in their lithium batteries, it seems only logical that they pose an even greater fire risk. Not so, says Sebastian Hoerold, Head of Technical Service Thermoplastics & Market Manager Flame Retardants at Clariant: “The fire risk of electric vehicles is not higher but different from traditional cars with combustions engines.”
Not more but different risks
Electric power trains work at much higher voltages and currents. Most conventional cars carry a twelve-volt battery to run the starter, lights, and all onboard electronics. Even so-called mild hybrids, in which a powerful electric motor supports the combustion engine, run on just 48 volts. In contrast, some all-electric vehicles have fast-charging cycles that can involve 800 volts or more.
Then there are the differences in everyday use: Parking a diesel essentially puts the car to sleep. But parking an EV usually involves charging it. “We see some of the highest voltages and currents precisely as the car is unattended,” says Hoerold. “That can be overnight in your garage or during the day in a public parking area, say, underneath a busy shopping centre or an office building. It is this combination of high-energy batteries, high voltages and currents during charging while being unattended that needs to be considered in safety standards.”
High voltages, tight spaces
“Up until recently, the automotive industry was not much of a market for our high-performing flame retardants. However, that is about to change dramatically,” says Elmar Schmitt, Segment Manager for Clariant's flame retardant business. “In reinventing their product, carmakers will need new materials with safety built in to deal with a whole new set of challenges and requirements.”
First, there are the high voltages. These can cause short-circuits and sparks that can ignite flammable materials. One of the ways to prevent such failures is by design: Simply placing conducting parts further apart is one strategy. Another is to encase components. But these approaches aren't always practical in car design. For one, cars are crammed with ever more electric hardware. Spaces are tight. Components need to fit close together. Adding material and assembly work to encase components drives up costs and adds weight. “Carmakers have always been sensitive on these two fronts,” says Schmitt. “Even small extra costs add up quickly, so does excess weight. Every gram you can shave off an EV adds to its battery range, which is currently one of the most important selling points.”
Resistant and lightweight
High-voltage plugs, connectors, bus bars and other electrical components require high-performing polymers with high-performance flame retardants – such as Clariant's Exolit®. It has been in use for two decades in some of the most demanding industries, from smart consumer electronics to home appliances to industrial applications. Based on organic phosphorus compounds, Clariant's additives can stop plastics burning within seconds and thus stop flames from spreading. It also helps minimize the risk of creepage and sparks. Exolit is non-halogenated, which makes it safer and more environmentally compatible than most solutions in the market. According to Schmitt: “But it is the improved material performance that makes it especially appealing to the EV industry.”
Adding Exolit to plastics does not affect or in some cases even improves their electrical properties – measured as the Comparative Tracking Index (CTI). “We enable manufacturers to reach Performance Level Category 0, which holds for 600 volts,” Hoerold explains. “That way, conducting parts can be fit closer together, allowing further miniaturisation and weight cutting.” Plus, Exolit itself adds remarkably little weight to the parts.
Then there is the matter of durability. Standard cars are expected to last up to 200,000 miles. With fewer moving parts, EVs may get even more mileage. However, that heavily depends on how well connectors, plugs, cables, brackets, and the likes hold up to the constant stress caused by vibration, extreme temperatures, UV light, corrosive liquids, dust and moisture. High voltages and humidity can further exacerbate this stress through a process called hydrolysis. “Over time, it can break down materials within the polymer and lead to corrosion in the pins and connectors,” Hoerold explains. “Exolit is hydrolysis-stable and can be used in dedicated hydrolysis resistant formulations as well.”
Probably the most important draw to carmakers is how little the addition of Clariant's flame retardants affects a polymer's other properties. “The automotive industry has made an art of engineering cars to optimise costs, production speed, durability, and so on,” Schmitt says. “They want their polymers to perform the way they're used to.” However, most flame retardants make plastics more brittle, less workable, and even less durable overall. Some make specific production processes harder or even impossible. With Exolit, Clariant has carmakers covered as they are very satisfied with the way it works with both laser welding and laser marking. Plus, it affects the physical properties of the plastics as little as possible.
Aiding the revolution
In EVs, the colour orange is a safety feature. It indicates high voltage components and cables. Meeting and maintaining this specific standard colour throughout the entire lifetime of a car is crucial. Some flame retardants can make it impossible to colour parts accordingly. Exolit can be used for any colour. Other flame retardants can also cause heat-related discoloration over time. “Our solution affects the colour of the polymer less than any other product,” Hoerold says.
It is clear that high-performing flame retardants are crucial in EVs. “The industry standards and regulations on fire safety are not completely finalised yet,” says Schmitt. “But we know that products such as Exolit will have a role to play that goes beyond fire safety. Combining high fire safety standards and high CTI with good mechanical properties and sustainable chemistry will help make electric vehicles more efficient and reliable. That in turn will instill greater confidence in EVs and thus help expedite the electric revolution around the world. It’s one of many ways in which Clariant helps build a sustainable infrastructure and promote the kind of immediate climate action we need to reach the Sustainable Development Goals.
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