The Internet of Things (IoT) and e-mobility are essential technologies of the 21st century with exponential growth. Passive fire safety regulations and standards must be adapted to these new challenges. Flame retarded products help to meet fire performance requirements and to better protect life and property.
Dr. Jürgen Troitzsch is fire safety consultant at the Fire and Environment Protection Service (FEPS).
Connectivity and mobility are megatrends revolutionizing our daily life. Market studies show that the number of connected IoT devices is expected to globally grow from 6 billion in 2015 to around 30 billion in 2025, implying a substantial growth of electrical devices. For e-vehicles, it is estimated that until 2025 the global passenger e-vehicles fleet will grow to over 50 million, e-buses to around 6 million, and electrical two- and three-wheelers to over 300 million units.
In these new, future-oriented technologies, it is essential to consider the impact of combustible materials and components on fire safety. The quickly growing number of physical objects used in IoT applications, mainly electrical devices embedded with software, sensors and other technologies to connect and exchange data over the internet, and the exponential growth of e-vehicles requires high fire safety standards to protect life and property.
Fire statistics and recalls
Fire statistics show that the number of all fires and fire deaths, including that of structural fires and highway vehicle fires, decreased from 1980 to 2020. However, although home electrical fires showed a similar trend over the last 40 years, the related number of fire fatalities (471 in 1980) showed distinct fluctuations from year to year and reached 480 fatalities in 2016.
The leading factors for conventional vehicle fires in the period 2013–2017 were mechanical failures or malfunctions (47%), followed by electrical failures or malfunctions (21%). In 2020, the share of e-vehicles accounted to approx. 1% of the global fleet, and thus did not yet appear in the statistical data.
Although a lot of progress has been made in the last 40 years, the success in taming fires has unfortunately led to fire safety taking a back seat to other societal concerns that seem more pressing. Exponentially growing new technologies may lead to increasing challenges to fire safety, i.e. to IoT-related consumer electronics, and e-vehicles using lithium-ion batteries. To prevent these technologies from becoming fire hazards, improved fire safety requirements and standards need to be developed/updated, and consumers educated on potential risks.
In addition to fire statistics, recalls provide important information on fire safety issues of e-devices related to IoT and of e-vehicles. The main international recall website portal run by OECD covers all major recalls including electrical devices and automotive. Over the period of the last 10 years (October 2011 to October 2021) 3,726 fire-related records were found.
Electrical fire hazards occurred mainly from electrical supplies (812), home appliances (260), and computing (47). For products used in automotive, 727 recalls were linked to fire hazards with 78 recalls related to electrical fires and 43 related to battery fires. The recalls show that one of the main causes for fires resulting from malfunction (overheating, electrical components failure, etc.) is the use of non-flame-retarded plastics not meeting the existing fire safety requirements, or that the requirements themselves are too low.
Fire safety requirements
For E&E equipment used in IoT applications, fire safety requirements for plastic parts in electrical devices and appliances must be met. Overheating, glowing parts, short circuits, and small open flames are realistically simulated by ignitability and flammability (glow wire and small flame) tests. They reduce the risk of fire to a tolerable level even in the event of foreseeable (mis)use, malfunction, or failure.
Fire safety requirements and tests for conventional and e-vehicles interiors are too low and E&E products are virtually not regulated. Modern cars and e-vehicles require higher fire safety levels, because an increased fire hazard arises from the multitude of electrical devices now present in cars and from the electric motor, which can reach voltages of 400 to 600 V, versus 12 or 48 V for vehicles still used today.
Road vehicles still must meet the old fire safety requirements of 1972 for car interiors to U.S. FMVSS 302. They do not consider the fire safety needs of modern vehicles. Studies funded by the U.S. National Highway Traffic Safety Administration are underway, but no convincing alternatives have been found so far.
To address the new fire safety challenges for e-vehicles and external charging stations, requirements and test specifications were taken over for electric powertrains and Li-ion batteries components, enclosures, plugs, and sockets.
Annex 8E of UNECE (United Nations Economic Commission for Europe) Regulation 100 describes a fire test for the rechargeable energy storage system against exposure to fire from outside of the vehicle to allow driver and passengers enough time to leave the vehicle.
To ensure the safety of electric vehicles charging stations, fire safety requirements for plastic components such as enclosures, plugs and sockets have to be met in Europe with ignition and flammability (glow wire), and in the USA with the more demanding open flame propagation tests.
Fire safety requirements for batteries address the whole battery system and not specifically fire performance requirements for materials and components. The focus is on mechanical, thermal and electrical abuse tests with forced internal short circuit and a resulting fire.
Plastics used in electric vehicles’ Li-ion batteries enclosures, covers, end plates, cell holders, spacers and high-voltage connections must meet open flame propagation test specifications.
Passive fire safety and flame retardants
Passive fire safety needs of electrical equipment in IoT applications and e-mobility are met with E&E products usually containing flame retardants, because they are very efficient, easy to process, and meet technical requirements. The flame retardants used are mainly based on additive, reactive, polymeric brominated, phosphorus, nitrogen, and inorganic compounds. They help to meet the most demanding and realistic ignition, flammability and flame propagation tests.
Inherently flame retarded products are used in specific cases, but they may be difficult to process and expensive. Thermal runaway prevention of single battery and battery module interiors with temperature peaks of up to 900°C can be achieved with intumescent coatings, interlayers such as mica, aerogel sheets, or ceramifying products based on silicone.
The exponential growth of plastics in IoT and e-mobility requires products with improved fire safety. For appliances used in IoT, the ignition, flammability and flame propagation test specifications generally provide acceptable fire safety levels with flame retarded electrical products. However, recalls have shown that in some cases requirements are not met or too low. Therefore, fire safety requirements and standard specifications need to be regulated and adapted for products used in IoT.
For e-vehicles, higher fire safety levels are essential because of the increased fire hazard from high voltage, Li-ion batteries, and the countless electrical devices used. The globally used 1972 U.S. MVSS 302 flammability test for car interiors no more addresses the fire safety needs of modern road vehicles. Here, more adequate and stringent regulations and tests must be developed.
Parallel to the USA, developments through UNECE in Europe could accelerate this process. The already introduced fire test for rechargeable energy storage systems to UNECE Regulation 100 is a first step in the right direction. Flame retarded plastics in modern e-vehicles averting fire hazards, intumescent coatings, interlayers and ceramifying products preventing thermal runaway of batteries will help to meet these fire safety challenges.