It had been confidently hypothesized for years that modern vehicles burn differently, due to the vast array of material and fuel-source changes over the years. Although it was logical to suggest that fuel loads in modern parking structures have increased, without substantial evidence pointing to a problem, it was just theories and hypothetical scenarios until New Year’s Eve 2017 when these unimaginable theories and scenarios played out in real time.
Unprepared for parking garage response
The fire-safety community stood in awe as the King’s Dock Car Park fire1 in Liverpool, England unfolded. A 4,930m2 (53,000ft2) open-air concrete parking garage was consumed by fire. The fire started in a single vehicle’s engine compartment and had spread to nearly 20 vehicles by the time the fire service arrived on scene. Despite continued suppression efforts, the hazard kept evolving, and its intensity quickly exceeded the fire brigade’s extinguishing capabilities. Temperatures soared. Rubber tires exploded. Plastic fuel tanks ruptured. Burning gasoline flowed down ramps. Drainage gutters melted from the burning fuel. Fire spread between levels. Concrete broke off in fragments. The structural integrity of the garage was compromised. And about 40 hours after the fire broke out, more than 1,150 vehicles on eight stories were destroyed and the King’s Dock Car Park fire finally ceased burning.
While incidents of this severity are rare, the number of vehicles involved and the time to contain the fires have been inching up in recent years. For example, between 1995 and 1997, 98% of parking-structure fires involved less than four vehicles and none involved more than seven cars, while 14% of parking structure fires in 2014 involved more than five vehicles. Recent incidents like the one in Liverpool show us, quite vividly, that this trend is persisting.
The evolution of vehicle fire hazards is not surprising, considering the pace of technological innovation and material advancement in our society. The global tally of vehicles has now surpassed 2 billion worldwide,2 and with this market growth has come government efficiency standards in the United States, Europe and China that are driving modern vehicle design trends today. According to the National Highway Traffic Safety Administration’s (NHTSA) Corporate Average Fuel Economy (CAFÉ) standards, passenger vehicles are expected to average 54.5 miles per gallon (4.3 L/100km) by 2025 in the US while European standards have set a target of 37.5% reduction in CO2 emissions between 2021 and 2030.
These global efficiency goals have pushed automotive manufacturers to make vehicles more affordable, safer, lighter and more fuel efficient. So, parts that were historically metal, cast-iron, or aluminium, are now made of plastics or fiberglass. Everything from bumpers to gas tanks to the intake manifold in the engine are now made of plastics. On the interior of the vehicle, many combustible and synthetic materials are used, and the increase in electronics presents additional fuel and ignition sources. Likewise, environmental goals have led to increased use of alternative-fuel vehicles, such as battery electric, hydrogen fuel cells, liquified natural gas (LNG) and other emerging technologies.
The sheer volume of vehicles has driven change in the parking industry too. As developers look for parking solutions in areas where land is immensely valuable, the area afforded to each vehicle has been reduced, and stackable garage configurations are gaining popularity as automation and mechanization become more advanced and affordable. Beyond construction changes, many garages are also integrating electric charging stations and photovoltaic systems into their designs – presenting additional hazards.
While the benefits of fuel-efficient vehicles and spatially optimized parking structures are clear, it has left researchers and code developers concerned about what such densely packed arrangements of modern vehicles may mean for fire protection – and emergency response.
By the numbers
To help navigate the new world order of vehicle and parking garage construction, the Fire Protection Research Foundation, the research affiliate of the National Fire Protection Association (NFPA), in collaboration with SFPE Foundation, began a research project centred around the impact of modern vehicle hazards on parking structures and vehicle carriers3 in 2019.
The overarching research goal was to quantify the fire hazards associated with modern-day vehicles, parking structures, and vehicle carriers through a literature review and hazard assessment to better inform NFPA technical committees, such as those responsible for NFPA 13, Standard for the Installation of Sprinkler Systems,4 NFPA 88A, Standard for Parking Structures,5 and NFPA 301, Code for Safety to Life from Fire on Merchant Vessels.6
The Phase I study, led by Combustion Science and Engineering (CSE), found the average US vehicle in 2018 to contain 91% more plastic by weight than the average vehicle in 1970. Interestingly, despite the drastic change in materials, the fire intensity and total energy released from vehicles over the course of decades was found to be relatively constant – roughly 7-megawatt (MW) fires or larger – according to the limited available literature and test data.
What has changed, however, is the fire behaviour. The changes in construction materials have reduced the time to ignition, increased the probability of spread, and altered the behaviour of fire development. Research on older vehicles indicates that fire spread between vehicles in a parking-garage configuration could occur over 10–20 minutes, but once two or more cars are involved, the time to ignition for those additional vehicles is dramatically reduced (can be less than 5 minutes). Another contributing factor is that plastic fuel tanks can begin to show signs of failure after a 2–5-minute pool-fire exposure, which can result in a flowing liquid fire that exacerbates fire spread.
As more vehicles become involved, the prolonged high-temperature exposures on the load-bearing structural elements can threaten the integrity of the structure. During the Liverpool incident, the constant high-temperature exposures caused significant spalling of the concrete, which typically occurs when the internal temperature exceeds 374°C (705°F). This created large penetrations in the floor which contributed to vertical fire spread. The ceiling-level temperatures experienced from an inferno of modern vehicles can also cause failure of structural steel. Once the structure exceeds its critical thermal threshold of 538°C (1,000°F), the load-bearing capacity is reduced to half and may compromise the structure. As seen in the Stavanger Airport fire in Norway (2020),7 these conditions can lead to structural collapse of a multi-story parking structure.
Historically speaking, open parking garages were considered to have a low fire risk by most regulatory bodies. Although this assessment was substantiated by the research and fire-loss data available at the time, modern vehicles have evolved greatly since these regulations were originally established. Garages today; however, are still being designed based on data from 50+ year old vehicles.
Sprinklers and detection systems have historically not been required in open parking garages if they are constructed with non-combustible or limited combustible materials. Past regulations generally assumed that fire spread from one vehicle to another would not occur, and if it did the fire department would arrive in time to control it. It was also believed that allowing smoke to escape from an open parking garage perimeter would largely mitigate the fire risk. Based on these assumptions, a number of special allowances were permitted to reduce code requirements in open parking structures. While these standards are regularly updated, the fire-protection criteria for open parking structures has seen minimal changes over the years.
Many of these legacy assumptions were debunked by the King’s Dock Fire in Liverpool and the Stavanger Airport incident in Norway, among others. For example, while vehicle-to-vehicle fire spread had a low probability in the 1960s, this is no longer true today. Fortunately, regulatory bodies have taken note and are taking action to ensure that the protection guidance for parking structures keeps pace with the evolution of the hazards. Some of the proposed changes are showing up in codes and standards, including:
- The first draft of the proposed 2023 edition of NFPA 88A, Standard for Parking Structures, (6.4.2) now includes a provision for all garages, open and enclosed, to have sprinkler protection.
- The 2021 edition of the International Building Code (406.5) requires open garages to be sprinklered, when specific area and height limitations are exceeded.
- Some national codes within the EU now require sprinkler protection in open garages above a certain floor area, height, or when located below a hotel or assembly occupancy.
Despite the recent action on the regulatory side, many questions remain unanswered. Here are some that come to mind.
- What variables most impact fire spread?
- When and where should automatic sprinkler protection be required?
- What is the appropriate sprinkler design criteria needed to mitigate fire spread?
- What type of protection is needed for car stackers and automated garages?
- What is the appropriate protection criteria?
- Do fires involving alternative-fuel vehicles burn longer and require longer duration water supplies?
To further address some of the questions and needs of the regulatory and engineering communities, the Fire Protection Research Foundation and the SFPE Foundation are collaborating on a new research program, which is twofold. To support the needs of the regulatory community, part 1 will coordinate and establish data collection of full-scale modern vehicle burns to quantify the fire-spread characteristics and clarify critical sprinkler design requirements. And similarly, to support the needs of design engineers and property managers, part 2 will develop a fire-risk assessment tool that can inform the use of appropriate fire-protection measures.
Regardless of your role with parking garages – whether you park in them, design them, have one attached to your facility, or insure garages – this research will help us all take a step in the right direction, enhance our understanding of the hazards, and ensure that safety decisions are in lockstep with modern-day materials and practices.
For more information, go to www.nfpa.org