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Contents
  1. 1Why car park fires are a special case
  2. 2Fire load and heat release rate of cars
  3. 3Fire spread between vehicles
  4. 4Design fires for car parks
  5. 5Protection measures
  6. 6Firefighting in car parks
  7. 7Limitations and open questions
  8. 8See also
  9. 9Notes
  10. 10References

A car park fire is a fire in a building or structure used for parking motor vehicles, usually starting in one car and able to spread to the cars parked next to it. In the Netherlands, the 2012 Building Decree classifies an indoor car park as an "other functional use for parking motor vehicles".[1] A single burning car reaches a peak heat release rate of several megawatts; Introduction to Fire Safety Engineering uses 8.5 MW as a reference value.[2] Because an indoor car park is a large space of limited height, such a fire quickly produces very high temperatures and dense black smoke.[3]

Car park fires are not frequent, but large ones can involve 10 to 50 or more vehicles and damage the building and the functions above it.[3][4] Major fires in Paris, Liverpool and Stavanger showed that standard design principles had not kept pace with the real behaviour of modern cars. These cars contain more plastic and therefore have a greater fire load and a higher heat release rate than older steel models.[3] Design guidance responds with design fires for car parks, sprinklers, ventilation and compartmentation, while fire services have to accept that an attack inside a large car park is often not safe.[5][6] Parking and charging of electric cars adds new questions, which are treated in the article on electric vehicle fires.[7]

Why car park fires are a special case

Fire safety has always been a dilemma in indoor car parks, even before electric vehicles appeared. The design parameters of most existing car parks were based on older cars with little plastic, burning petrol or diesel.[3] According to a 2015 study by DGMR, cited by the Netherlands Institute for Public Safety (NIPV), the assumptions behind the safety of existing car parks are now demonstrably outdated. A different fire development and higher heat release rates have reduced the safety of car parks and of the buildings above them.[4]

The geometry of a car park makes conditions worse for the fire service. The heat, the loss of visibility, the long hose distances and the difficulty of finding one's way all make reconnaissance and firefighting difficult and risky.[3] In the fire in the Singelgarage in Alkmaar on 1 July 2020, poor visibility made it hard to find the burning cars. A firefighting robot was used, and a police robot towed out an electric car whose battery kept reigniting.[4]

A car park fire can also affect people far from the parked cars. On 26 February 1993 a bomb in a van on the B2 level of the parking garage under the World Trade Center caused an explosion and a subsequent fire. Smoke entered damaged lift shafts and reached the 44th floor of the North Tower about one minute after the explosion.[8] Under the 1968 New York City Building Code, the parking garage was the only part of the two towers that was originally sprinklered.[9]

The probability of a car park fire is still uncertain. There are no reliable datasets on the occurrence of fires in electric vehicles, and the role of production defects and ageing is unknown.[3] NIPV therefore frames the main question as one of consequences. Even though fires in indoor car parks are not frequent, their effects must be socially acceptable and the measures must be tailored to them.[4]

Fire load and heat release rate of cars

The fire load of one car is between 6,000 and 12,000 MJ, compared with about 1,900 MJ for a three-seat sofa.[10] Expressed per floor area, a Swiss survey of 1967 to 1969 found a fire load of 200 MJ/m² in parking buildings.[11] In New Zealand, C/VM2 (second edition, 2025) prescribes a design fire load energy density of 400 MJ/m² for car parks. For car stacking systems it prescribes 400 MJ/m² per tier of car storage.[12]

Measured peak heat release rates of single cars vary widely. Tests at the Fire Research Station gave a peak of 8.5 MW for a 1982 Austin Maestro and 4.5 MW for a 1986 Citroën BX. Tests at VTT on cars from the late 1970s gave peaks of only about 1.5 to 2.0 MW. Babrauskas notes that the reason for the spread is not fully clear and that it is not due to the polymer content.[13] The highest of these values equals the reference peak of 8.5 MW for a car in Introduction to Fire Safety Engineering.[2]

More recent reviews give similar orders of magnitude. A literature review by Sun and co-workers, summarised by NIPV, found a peak of about 6 MW for both electric and conventional cars. The total heat released by conventional cars was 3.3 to 10 GJ. The average for a mid-range conventional car was about 6.8 MW.[14]

A typical passenger car fire burns for just over half an hour and reaches a maximum of about 5 MW after 10 to 15 minutes.[15] For car parks, the fire scenario is usually described by a heat release rate curve rather than a temperature curve. The heat release rate determines how quickly air and objects heat up, how fast the fire grows and how much smoke is produced.[16]

Fire spread between vehicles

The main hazard in a car park is fire spread from car to car. In tests by TNO in the late 1990s, fire could spread to the adjacent parked cars 10 to 15 minutes after the first car ignited, depending among other things on the distance between them.[17] The Dutch standard NEN 6098 for smoke control in mechanically ventilated car parks contains a design curve based on these tests. In the curve, three cars are burning 15 minutes after ignition, which the book regards as a conservative scenario.[17]

The NEN 6098 curve combines the curves of three cars that ignite one after the other. Read from the graph in the book, the first car peaks at about 6 MW, and the total reaches about 9.4 MW some 22 minutes after ignition. The curve then falls to zero at about 32 minutes, because the intervention of the fire service is included.[17] Because cars now contain more plastic, the book warns that such curves may be less conservative than intended and should be checked against current vehicle scenarios.[17]

Line chart of heat release rate against time for three cars and their total, peaking at about 9.4 MW after about 22 minutes.
Design curve for a car park fire in NEN 6098: three cars ignite one after another and the total peaks at about 9.4 MW. Based on Van Rossum (2027), §8.6.

NIPV calls fires that pass from vehicle to vehicle "travelling car fires", because they move through the car park, as it were.[7] The greater speed of fire spread and the higher heat release rate of modern cars make a long, intense fire involving 10 to 50 or more vehicles more likely. This applies to closed and open car parks and even to outdoor car parks.[3] In an open car park with largely open façades, heat and smoke can escape to the outside. Strong winds, however, can increase the probability of fire spreading from one car to the next.[18]

Automatic and semi-automatic parking systems increase the risk of large fires involving several cars. The cars are much closer together, on top of, underneath and next to each other. The structure heats up more quickly, the hydraulic oil of the system adds fire load, and the cars are hidden from view.[19] Firefighters cannot enter such systems because of the risk of falling and being trapped.[19]

Design fires for car parks

Fire engineers describe the growth of a car park fire with a design fire. In New Zealand, C/VM2 (second edition, 2025) uses a t-squared fire for car parks without stacking: the heat release rate grows with the square of the time since ignition. The growth stops at flashover, at the peak heat release rate, at the ventilation limit or, in a life safety analysis of a sprinklered building, when the sprinklers operate.[20]

Q˙=αt2

Symbol Description Unit
Q˙ heat release rate of the design fire kW
α fire growth coefficient; 0.0117 for car parks without stacking kW/s²
t time since the start of the growth phase s

For car parks without stacking, C/VM2 sets the growth coefficient at 0.0117 kW/s² and caps the fire at a peak of 20 MW. This coefficient is a quarter of the fast value of 0.0469 kW/s² used for most other buildings, so any given heat release rate is reached in twice the time.[20] The 2013 commentary on the first edition of C/VM2 explains why. Car parks are one of the few uses in which the fuel can be bounded and its layout is controlled. A literature review showed that the early growth of car fires fits a medium t-squared rate.[21] For car parks with stacking systems, the growth is much faster, with a t-cubed relation that depends on the storage height and a peak of 50 MW.[20]

As a worked example, take the time for the design fire to reach 6 MW, the peak of a typical single car. With α=0.0117 kW/s², the time is the square root of 6,000 divided by 0.0117, which gives about 716 s or 12 minutes. The 20 MW cap is reached after about 1,307 s, or 22 minutes. After 10 minutes the design fire releases about 4.2 MW, which is close to the measured maximum of about 5 MW after 10 to 15 minutes for a typical car.[20][15]

Two t-squared curves: car park growth reaches 6 MW after 12 minutes, the fast curve after 6 minutes; dashed lines mark car peaks.
C/VM2 design fire for car parks without stacking (0.0117 t²) compared with the fast fire (0.0469 t²), with measured peaks of single cars. Based on Ministry of Business, Innovation and Employment (2025b), p. 20, and Babrauskas (2002b), p. 3-27.

The relation describes only the growth phase and starts from an established fire. The commentary notes that tests behind such growth rates use ignition burners of 10 to 40 kW, which skip the slow incipient phase. The method may therefore slightly over-predict the early growth.[21] C/VM2 also sets rules for the ventilation available to a car park fire. Only permanent openings in the perimeter walls and access ramps count, and car parks with overlapping interconnected floors are assessed for the worst floor or the worst pair of adjacent floors.[22]

Protection measures

Automatic suppression is the measure most often recommended for closed car parks. A sprinkler or water mist system can contain a fire to a small number of cars for a long time and so prevent a travelling fire.[5] The thermal load on the load-bearing structure then stays limited and short-lived. The risks of collapse, fire spread and smoke spread are reduced, escape and attack routes are more likely to remain intact, and the fire service is more likely to keep the situation manageable.[5] In a closed car park, where heat is removed less quickly, NIPV regards a sprinkler system as the most obvious measure. In open car parks, weather makes sprinklers less suitable.[23]

Compartmentation is a second option. In the Netherlands, the 2012 Building Decree allows a fire compartment of up to 1,000 m² in a new car park and up to 3,000 m² in an existing one.[1] Further division into compartments, or screens between vehicles, can confine a travelling fire. Smaller compartments, however, heat up faster, may reach flashover conditions and make the burning car harder to locate. NIPV therefore prefers an open, clearly arranged area with sprinklers.[24]

Early detection gives more time for escape and response. The Dutch Building Decree requires an automatic fire alarm system with full detection in enclosed car parks larger than 1,000 m². In one comparative study, carbon monoxide detectors gave the fastest alert.[25] Detection only helps if the alarm is followed up quickly, which is a particular concern in residential buildings.[25]

Ventilation is mainly a tool for the fire service. In tests of jet fan ventilation in closed car parks, TNO derived the design fire later adopted in NEN 6098.[17] Displacement ventilation can create an air speed of about 1.5 m/s over the full cross-section, following NEN 6098, which can easily mean forty-fold ventilation. It gives firefighters a view of the fire but works only in tunnel-shaped car parks, and it usually starts after people have left.[26] Smoke and heat extraction systems, mostly with zero- to ten-fold ventilation, are effective mainly for clearing smoke after the fire is out.[26] For large underground car parks, Dutch guidelines sometimes require a computational fluid dynamics simulation, to show that the ventilation allows the fire service to work under acceptable conditions.[27]

Firefighting in car parks

Fire services prefer to fight a fire from the outside. An interior attack is made only in a small structure, when an exterior attack fails and when it can be done safely.[28] A car park is a large structure in which doors cannot be closed to limit the air supply, and the depth of attack is often considerable. NIPV therefore concludes that an offensive interior attack in a car park is generally not safely possible. The commanding officer on site decides whether to attempt one.[6] If no offensive attack is possible, the fire service fights the fire defensively from outside, and the car park is considered beyond saving.[29]

The type of car park changes the problem. In an underground car park, rising smoke hides the cars and the burning vehicle cannot be located from outside. A smoke-free stairwell with a dry riser connection can serve as the attack route and shorten the attack depth.[30] In a multi-storey car park, fire can spread to several storeys, and crews must find the stairwell, carry hoses and bridge the levels.[31] Where a residential building stands above the car park, letting the fire burn out is hardly an option, so fire resistance needs extra attention.[31]

Two car park sections: open deck with smoke leaving sideways; smoke-filled underground level entered from a stairwell with a dry riser.
Open car park (left): heat and smoke leave through the open façades. Underground car park (right): smoke fills the level and the crew attacks from a smoke-free stairwell with a dry riser. Based on Van der Graaf et al. (2021/2023), pp. 48–51.

Water flow must match the size of the fire. As rules of thumb, a high-pressure jet of 125 L/min is generally sufficient for a fire of up to 2.5 MW. A low-pressure jet of 450 L/min is generally sufficient for up to 10 MW. International practice for a car close to the entrance is to use two low-pressure jets.[6] The operating time of a sprinkler system, typically 30 to 120 minutes, limits the time available. If the fire service cannot enter within that time, several cars may catch fire and the car park may still burn out.[32]

Limitations and open questions

Design fires for car parks rest on tests of older cars. NIPV notes that Dutch regulations, standards and guidelines are still based on fires in conventionally fuelled vehicles, and it calls for a standard with heat release rates based on the latest information.[3][33] Measured car fires differ by a factor of four or more, so the choice of a single design value carries large uncertainty.[13] The 2015 DGMR study judged the probability of a large multi-vehicle fire to be higher than even recent statistics suggest, and too high to ignore in design regulations.[3]

A common misconception is that the fire service will always be able to put out a car park fire. Fire service deployment is a best-efforts obligation and not a substitute for prevention, and its outcome is by definition uncertain.[34] NIPV stresses that developers, architects and owners should be told that firefighters will not automatically enter, and that a car park may burn out.[32] The Dutch Building Decree aims at preventing casualties and spread to another plot; damage to the car park itself is left to agreements between owners and insurers.[35]

See also

Notes

  1. ↑ 1.0 1.1 Van der Graaf et al. (2021/2023), p. 14.
  2. ↑ 2.0 2.1 Van Rossum (2027), §4.5.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Van der Graaf et al. (2021/2023), p. 11.
  4. ↑ 4.0 4.1 4.2 4.3 Van der Graaf et al. (2021/2023), p. 12.
  5. ↑ 5.0 5.1 5.2 Van der Graaf et al. (2021/2023), p. 36.
  6. ↑ 6.0 6.1 6.2 Van der Graaf et al. (2021/2023), p. 45.
  7. ↑ 7.0 7.1 Van der Graaf et al. (2021/2023), p. 29.
  8. ↑ Ferreira and Strege (2005), p. 57.
  9. ↑ Lew et al. (2005), p. 162.
  10. ↑ Van Rossum (2027), §4.4.
  11. ↑ National Research Council of Canada et al. (2005), p. 3.4-6.
  12. ↑ Ministry of Business, Innovation and Employment (2025b), p. 22.
  13. ↑ 13.0 13.1 Babrauskas (2002b), p. 3-27.
  14. ↑ Van der Graaf et al. (2021/2023), p. 25.
  15. ↑ 15.0 15.1 Van der Graaf et al. (2021/2023), p. 26.
  16. ↑ Van der Graaf et al. (2021/2023), p. 24.
  17. ↑ 17.0 17.1 17.2 17.3 17.4 Van Rossum (2027), §8.6.
  18. ↑ Van der Graaf et al. (2021/2023), p. 48.
  19. ↑ 19.0 19.1 Van der Graaf et al. (2021/2023), pp. 50–51.
  20. ↑ 20.0 20.1 20.2 20.3 Ministry of Business, Innovation and Employment (2025b), p. 20.
  21. ↑ 21.0 21.1 Ministry of Business, Innovation and Employment (2013), p. 55.
  22. ↑ Ministry of Business, Innovation and Employment (2025b), p. 18.
  23. ↑ Van der Graaf et al. (2021/2023), pp. 49–50.
  24. ↑ Van der Graaf et al. (2021/2023), p. 35.
  25. ↑ 25.0 25.1 Van der Graaf et al. (2021/2023), p. 37.
  26. ↑ 26.0 26.1 Van der Graaf et al. (2021/2023), p. 38.
  27. ↑ Van Rossum (2027), §11.2.
  28. ↑ Van der Graaf et al. (2021/2023), p. 43.
  29. ↑ Van der Graaf et al. (2021/2023), p. 44.
  30. ↑ Van der Graaf et al. (2021/2023), p. 51.
  31. ↑ 31.0 31.1 Van der Graaf et al. (2021/2023), p. 52.
  32. ↑ 32.0 32.1 Van der Graaf et al. (2021/2023), p. 47.
  33. ↑ Van der Graaf et al. (2021/2023), p. 54.
  34. ↑ Van der Graaf et al. (2021/2023), p. 41.
  35. ↑ Van der Graaf et al. (2021/2023), pp. 15–16.

References

  • Babrauskas, V. (2002b). Heat release rates. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 3-1–3-37). National Fire Protection Association; Society of Fire Protection Engineers.
  • Ferreira, M. J., & Strege, S. M. (2005). Smoke management systems (NIST NCSTAR 1-4D). National Institute of Standards and Technology.
  • Lew, H. S., Bukowski, R. W., & Carino, N. J. (2005). Design, construction, and maintenance of structural and life safety systems (NIST NCSTAR 1-1). National Institute of Standards and Technology.
  • Ministry of Business, Innovation and Employment. (2013). Commentary for Building Code clauses C1–C6 and Verification Method C/VM2.
  • Ministry of Business, Innovation and Employment. (2025b). Verification Method C/VM2: Framework for fire safety design (2nd ed.).
  • National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). International fire engineering guidelines (2005 ed.). Australian Building Codes Board.
  • Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). Fire safety of indoor car parks accommodating electrically powered vehicles. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
  • Van Rossum, E. (2027). Introduction to Fire Safety Engineering. Fire Safety Academy.
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