Sprinkler Design for Car Parks: Reducing the Impact of Electric Vehicle Fires

Arda Baydemir

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29 Sep 2023

Ensuring the safety of people and property is crucial to any building, and car parks are no exception. This includes reducing the risk of harm from electric vehicle fires. A well-designed sprinkler system in a car park and other building areas can control fire spread and provide sufficient time for evacuation, potentially saving lives. In addition, sprinklers help limit property damage.

Car parks usually sit within or in the proximity of occupied areas or high-value assets and can host a large number of vehicles and occupants daily. For sprinkler design, the challenge lies in selecting the correct code to align with the protection objectives of the system. This article explores the importance of sprinkler design in car parks, different applicable UK and US standard approaches, and recent changes within the codes.

Fire Risks Associated with Electric Vehicles in Car Parks

The plastic content of cars has increased over time, and recently, there has been a significant shift towards electric cars. Electric vehicles (EVs) have lithium-ion batteries that house ignitable liquids, which can lead to challenging, high-consequence fires under the right circumstances.

If lithium-ion batteries are in a fault situation due to physical damage, overheating or overcharging, then the phenomenon known as thermal runaway might occur, which can lead to toxic gas release and fire if the material is ignited. Charging facilities in car parks introduce potential ignition sources and risk of overcharging, increasing the probability of having a fire event in a car park.

Sprinklers: The Preferred Active Fire Protection in Car Parks

Adequate protection measures are necessary to mitigate the potential fire risk associated with electric vehicles, and sprinklers play a key part in this. The expectation of sprinklers is that they will control the fire rather than fully extinguish it or stop thermal runaway. By helping to limit fire spread, sprinklers provide more time for evacuation, reduce property damage and provide greater protection for firefighters.

On 11 July 2023, the UK Government’s Office for Zero Emission Vehicles published interim guidance in Covered Car Parks: Fire Safety Guidance for Electric Vehicles. The document acknowledges that sprinklers effectively control fire development within covered car parks and should be considered part of a cost-benefit analysis when designing new open-sided/enclosed car parks. It recommends BS EN 12845:2015 +A1:2019 and BS 9251:2021 as the appropriate codes for life safety, and also Loss Prevention Council (LPC) rules to satisfy property insurance requirements.

The UK Fire Protection Association (FPA)’s RISC Authority have published Version 2 of their guidance document RC59: Recommendations for Fire Safety When Charging Electric Vehicles, which outlines recommendations to mitigate the fire risk. It highlights the effectiveness of sprinkler systems: “Sprinklers provide the best form of active fire protection for enclosed car parks.” RC59 recommends following LPC rules incorporating BS EN 12845 but also refers to equivalent and recognized rules such as NFPA 13 and 88A.

Sprinkler Design Requirements for Life Safety

Sprinklers can be provided for life safety, property protection, or both. Determining the objective behind the requirement for sprinklers is the first step in developing sprinkler design.

Ultimately, the life safety requirements of a sprinkler system are driven by the need to satisfy British Standards and other Building Regulations guidance. Alternatively, sprinklers may be required to support fire engineers’ performance-based solutions, such as a reduction in required fire resistance to structure. The following British Standards address life safety in car parks.

BS 9251:2021: This code applies primarily to residential and domestic premises for life safety protection. The code only provides guidance for car park fire compartments up to 100 square meters and refers to BS EN 12845 if that limit is exceeded.

BS EN 12845:2015: This code applies to commercial and industrial premises as well as residential premises when directed by BS 9251:2021. Although the code’s National Foreword states that it is not only for life safety, adopting the code alone and ignoring the LPC rules is widely interpreted by property insurers to mean that the aim is life safety protection and the design is not intended for property protection.

Hazard classification determines the water density, water supply duration and area of operation in sprinkler system design. An increase in the hazard classifications means at least one or more of these parameters are more onerous, requiring larger water tanks, powerful fire pumps, and probably larger sprinkler heads and pipes.

BS EN 12845’s current classification of car parks is Ordinary Hazard 2 (OH2), but an updated code is due to be released soon. The document shared for public consultation indicates that the car parks will be equivalent to minimum Ordinary Hazard 3 (OH3) using the current version’s classification. This would mean an approximately 50% larger water tank volume. The design specifications will be more demanding than OH3 depending on the new variable criteria, specifically with regard to the ceiling height. The new version claims that systems designed in accordance with it will provide protection of life and property and mitigate business interruption.

Sprinkler Design Requirements for Property Protection

Sprinkler requirements for property protection generally come from the property insurer. Alternatively, the end user may decide to invest in the sprinklers to enhance business continuity in the aftermath of a fire.

If property safety is the primary goal of the sprinkler design, then the following codes and standards should be adhered to. Note that all three insurance-driven sprinkler codes/rules have recently upgraded the car park’s hazard classification, with the UK’s LPC rules being the most conservative.

LPC rules incorporating BS EN 12825: Loss Prevention Council (LPC) rules come in the form of technical bulletins (TB). The September 2022 version of the relevant TBs, particularly TB229 and TB202, increased the car park hazard classification to High Hazard Process 3 (HHP3), overriding BS EN 12845:2015’s current classification of OH2. HHP3 requires approximately six times more water tank volume than OH2.

NFPA 88A and NFPA 13: NFPA 88A, Standard for Parking Structures, 2023 Edition, was approved as the American National Standard on 9 April 2022. Earlier versions of the code did not require sprinkler systems in some car park structures under certain circumstances (e.g., 2019 edition). The 2023 edition requires sprinklers to conform to NFPA 13, Standard for the Installation of Sprinkler Systems, regardless of circumstance.

NFPA 88A also regulates other risk mitigation measures, and some of these have become more onerous in its 2023 edition. Moreover, the 2022 edition of NFPA 13 has increased the automobile parking hazard classification from Ordinary Hazard 1 (OH1) to Ordinary Hazard 2 (OH2). This means an approximately 33% larger water tank volume.

FM Global Data Sheet 3-26: January 2021 Interim revision of the data sheet updated the hazard category for parking garages and car parks from Hazard Class 2 (HC-2) to Hazard Class 3 (HC-3). This means at least an approximately 50% larger water tank for an FM-compliant system, though it might be more depending on ceiling height. FM’s HC-3 water tank is approximately 44% less in volume than the LPC rules tank size.

Appropriate Code Selection is Key

As the number of electric vehicles steadily rises, so does the risk of lithium-ion battery fires. Sprinklers are recognized as an effective measure to mitigate this fire risk in car parks, with each car park project requiring a tailored approach to its sprinkler design. Given that all the codes mentioned above are applicable in the UK and Ireland, discussion is needed with project stakeholders, authorities and insurers to ensure that the code selection is appropriate before detailed design begins.

Jensen Hughes’ team of experts can guide you through the process of sprinkler selection and design development. Whether you need assistance upgrading an existing system or installing an entirely new system, our team will work closely with you to understand your requirements and develop a tailored solution that best suits your needs.

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About the author

Arda Baydemir
Arda is Jensen Hughes’ Head of Fire Systems Design for the UK and Ireland. He works closely with clients and design teams to achieve the fire protection safety goals of each project in cost-effective and innovative ways.