Iain Cumner, Managing Director of Patol Ltd, explores the evolving fire risks in car parks, focusing on vehicle design, construction materials and detection technologies

The fire industry is well aware that car parks present their own unique challenges in terms of effective fire safety. On 10 October 2023, that awareness filtered through to a much wider audience with the media reports on the major fire at the multi-storey car park at Luton Airport.

The headline figures helped to put into perspective the consequences: despite the efforts of 100 firefighters and 15 fire engines, who fought for 12 hours to bring the flames under control, more than 1,400 cars were written off, and the ensuing chaos disrupted the travel arrangements of some 34,000 passengers as 220 flights were cancelled.

The aftermath, while perhaps not providing sufficient fuel for front page headlines, still made for stark reading: the airport worked for months with the Motor Insurers’ Bureau (MIB) and the Association of British Insurers (ABI) to resolve claims and the car park rebuild project is not set to be complete until late 2025.

Thankfully such incidents are rare. But there is a growing concern they are likely to become more commonplace. Car parks and, importantly, the vehicles they contain, have changed significantly over the last few decades. Simply looking at the size of modern-day vehicles in comparison to their predecessors makes for interesting reading.

The Mini of 2018, for example, is over 60% larger than the launch model of 1959. The Range Rover, a much bigger car to start with, has still increased by over 40% in size compared to a 1981 model. The consequence is that the space between vehicles has been significantly reduced, this closer proximity making it easier for fires to spread from one to another and turning a minor incident into a major conflagration. The increase in the use of weight-saving plastic components in modern vehicle manufacture has also brought implications in terms of fire load.

The reference to Range Rovers takes us back to the Luton Airport incident. Despite ‘news’ circulating on the rumour factories that are Facebook and X (formerly Twitter) that an electric and/or hybrid vehicle was the source of the fire, it was subsequently proven by Bedfordshire Fire & Rescue Service to be a diesel-powered vehicle, widely reported to be a Range Rover. While the supposition that it was an electric vehicle proved to be incorrect on this occasion, this brings us onto another important consideration in car park fire safety.

‘Thermal Runaway’

Electric vehicles bring with them their own issues regarding fire risk. The lithium-ion batteries which power them can be subject to a rapid increase in temperature caused by the release of stored chemical energy in the event of a battery fire. This is referred to as ‘thermal runaway’ and can result in an explosive combustion of electrolyte vapour released from the battery. This generates intense heat, as well as highly toxic smoke and can contribute significantly to the potential for multi-vehicle fires.

The current advised approach for the fire service when faced with a fire in an electric vehicle is to allow a controlled burn. However, when the vehicle is within a confined space – a covered car park being a prime example – the fire may need to be extinguished to prevent spread. In an electric vehicle fire twice the amount of water is typically required to extinguish it compared to that for an internal combustion engine.

There is also an increased danger in terms of reignition. Add to that the growing number of electric vehicle charging points being installed in covered car parks, with the potential ignition sources they represent, and it is easy to see why concerns are being raised.

The combined issues of the increase in the adoption of electric vehicles along with the infrastructure to charge them, plus the typical size of a parking space, has been highlighted in a recent report by the ‘Office for Zero Emission Vehicles’ (OZEV) who only last year provided interim guidance. One of the recommendations is that the size of car parking spaces should be increased.

Construction contributing to the problem

It is important to appreciate that it is not only changes in vehicle design that are adding to the risk. Many modern car parks feature sloping floors to help with drainage from storey to storey. An unintended consequence is that this can also create a channel for any fuel that has escaped from vehicles to transfer through the whole structure.

Modern construction methods also focus on speed, providing cost savings as well as minimising disruption in the highly populated urban areas in which car parks tend to be located. This has seen the adoption of metal structures that are quick to erect but become malleable at high temperatures, providing the potential for instability in the event of a fire, particularly if the steel is uncoated.

Linear Heat DetectionCable

Car park fire safety was already becoming a topic of increased interest but what the Luton incident has undoubtedly done is to significantly raise the profile. Quite understandably the potential for sprinklers to become mandatory in multi-storey car parks is being discussed, with the design for the new car park at Luton incorporating a fire suppressant system. I would like to focus on the fire detection side of the equation and will leave it to those more qualified to discuss the pros and cons of extinguishing.

All those involved in the fire safety arena are only too aware that cost is inevitably a consideration in what is effectively a ‘grudge’ purchase. This is certainly true of car parks, with the muti-storey options offering a big area to protect.

This is one of the reasons why Linear Heat Detection Cable (LHDC) is increasingly being recognised as the fire detection method of choice in such applications. LHDC provides a cost effective option, with resettable (analogue) and non-resettable (digital) options available. While cost is a factor in its selection, LHDC is also ideally suited to the harsh environmental conditions that car parks typically present. Vehicle fumes, dust, damp and high humidity can all prove problematic for some forms of detection but they do not affect LHDC. It is also low maintenance and is not prone to false alarms.

Both systems are made up of a control device (optional for digital cable), the cable itself and an End of Line device. The technology is designed to provide early detection of fire conditions or overheating in circumstances where other forms of detection would not be viable due to cost and/or the inability to sustain a stable environment. A single detection zone of LHDC can cover from 1,600 to 2,000 square metres, with an alarm signal sent back from each zone to a control device which can be connected to a conventional fire alarm panel or fully integrated with an analogue addressable system.

Analogue LHDC is primarily used in car park applications.  It is a coaxial cable constructed with a copper-coated, steel central conductor, an inner insulation (dielectric), a tinned copper braid layer and an overall protective sheath. 

In a car park installation, a controller is typically employed and can be fully integrated on either a conventional fire panel or an analogue addressable system.  Monitoring a zonal length of cable for both elevated temperatures and faults, it can be configured to operate in two-wire mode that emulates the operation of conventional heat detectors.

It has the ability to trigger for hot-spot detection on small sections of the cable as well as an abnormal ambient temperature increase across the entire zone. An end of line termination box with test switches provides fault monitoring for both open and closed circuit faults, ensuring full cable integrity.

The cable is typically installed either on the car park ceiling or in a dedicated cable tray, with an air gap maintained between the ceiling or cable tray to ensure that they do not act as a heat sink towards the heat sensitive cable.

Dublin apartment blocks

A good example of how effective LHDC can be in protecting car parks from the threat of fire is a project for two blocks of apartments in Dublin. Custom Electronics, a commercial electronics provider based in Blanchardstown Dublin, offers a range of fire safety systems.  The company chose to fit Patol LHDC fire detection in both the Waterways Apartments in Rathbourne and the Oaks Apartments in Trimbleston, working on the latter project with electrical contractor Abbey Electrical.

Using specialist stainless steel clips and fixings, along with neoprene sleeves with cable ties, Patol’s LHDC was installed in parallel runs above the cars and access routes. Having the everyday appearance of simple cable means that the cable is less likely to suffer from wanton attack by vandals, a common problem for point-type detectors. For additional mechanical strength, it can be supplied in an armoured form.

Reflecting current and future risk

Car parks and the vehicles they contain have both changed significantly in their design over the years. The onus on maximising the number of vehicles a car park can accommodate is only getting stronger, with parking a perennial issue in many of the UK’s towns and cities.

This means that the space allocated per car is unlikely to increase significantly, ensuring that the potential for a fire to spread quickly remains. Nor is the focus on switching from fossil fuelled to electric fuelled cars going away, even if the date for banning the sale of new petrol and diesel cars has been pushed back to 2035. The fire threat that this poses has to be considered and somehow reflected in the fire solutions applied.

Regulations and standards are starting to develop but many, as in the case of electric vehicles, are still in preparation or under revision in most countries. The approach to safe car park design needs to consider all the contributory factors, from the building materials employed to the evolving designs of vehicles and the technologies available to protect them.

LHDC is not a panacea for car park fire safety. However, in the aftermath of the fire at Luton Airport, it can provide a significant contribution to the ongoing debate that we need to have to ensure that the risks are properly reflected in the measures taken to protect them.

This article was originally published in the January 2025 issue of International Fire & Safety Journal – to read your FREE digital copy, click here.