Industry·7 min read
Car Park Fire Safety: Dry Pipe Sprinklers, Smoke Control and Gas Detection
A car park is a fire scenario all its own — an unheated space, exhaust smoke and vehicle fire risk. Why freezing risk drives the choice of a dry pipe sprinkler, how zone size and water delivery time are limited in a dry system, when an accelerator becomes essential, and how exhaust smoke control and gas detection are set up — we explain the car-park-specific design from an engineering perspective.
A-Pro Engineering
A car park may look like a simple space at first glance, but from a fire standpoint it is one of the most demanding areas of a building. Vehicle fires carry a high heat load, the risk profile has shifted with the spread of electric vehicles, evacuation is constrained, and — the real engineering problem that is often overlooked — car parks are not heated. That single fact determines the choice of system type from the outset.
You can find which car park legally requires which system (600 m² / 10 vehicles for sprinklers, 1 July 2025 for detection) in our general guide. We won’t repeat the thresholds here; we go into the car-park-specific design engineering: the correct sprinkler type against freezing risk, dry system zone size and the accelerator requirement, exhaust smoke control, and gas/fire detection.
Unheated space and freezing risk: which system is right?
A standard sprinkler system is wet pipe: the pipes are continuously filled with pressurised water, and the moment a head opens the water flows immediately. This is ideal for heated areas. But in an enclosed car park the temperature easily drops below 0 °C in winter. When water freezes it expands; the expanding water cracks the pipes, joints and heads. The result: a system that delivers no water at all during a fire and, when it thaws, floods the ceiling.
That is why the solution in an unheated car park is a dry pipe sprinkler system:
- The pipes are filled not with water but with pressurised air or nitrogen.
- The water waits behind the dry pipe valve in a heated valve room; there is no water in the pipe run that could freeze.
- When a sprinkler opens, the air pressure in the pipe drops, the valve opens, and water fills the pipe and reaches the fire only at that moment.
Alternatively, pre-action systems are also used in sensitive or mixed areas; however, for an ordinary enclosed car park, the most common and economical correct solution is the dry pipe system. The dry system has a price — and that price forms the heart of the design.
The price of the dry system: water delay, zone size and water delivery time
A dry pipe system has a delay by its very nature: after a sprinkler opens, the water sweeps the air out of the pipes and only then reaches the head. Throughout this delay the fire keeps growing. Therefore the fundamental aim of dry system design is to keep this water delivery time under control.
This has two direct consequences:
- Zone (system) size is limited. The larger the system, the greater the volume of air to be swept and therefore the delay. That is why NFPA 13 limits the system volume connected to a single dry pipe valve: if the volume exceeds about 2,840 litres (750 gallons), it must be proven by hydraulic calculation that water reaches the most remote point within 60 seconds. The maximum area a single valve can protect is also limited (typically ≈4,830 m²); large car parks are divided into multiple zones.
- The design flow is increased. To compensate for the delay, the design (operating) area of the dry system is kept larger than that of a wet system — that is, it is calculated so that more heads discharge water at the same time.
In short, in a dry system the “just lay my pipe and put in the valve” approach doesn’t work; each zone is sized with a water delivery time calculation.
The accelerator requirement
The most effective way to shorten the water delivery time is to make the dry pipe valve open faster. This is exactly where the accelerator (quick-opening device — QOD) comes in:
The accelerator is a device that senses the pressure drop in the pipes at the very first instant. Under normal conditions the dry pipe valve waits for all the air in the pipe run to fall to a certain level; the accelerator, by transferring this pressure drop to the underside of the valve, triggers the valve much earlier. This way the water goes into service before all the air is released, and the delay is noticeably shortened.
In small dry systems (volume below ≈2,840 litres) an accelerator is often not needed. But in multi-storey, large car parks, when the system volume exceeds this limit, the only practical way to meet the 60-second water delivery requirement is usually to use an accelerator. The accelerator is a critical component that compensates, through engineering, for the biggest disadvantage of the dry system — the delay. (Another detail: because the residual moisture + air in the pipes of dry systems accelerates corrosion, in critical facilities the pipes are filled with nitrogen to provide protection as well.)
Exhaust and smoke control
In a car park fire the most deadly element is not the flame but the smoke. In an enclosed car park, smoke builds up rapidly, reduces visibility to zero and makes evacuation impossible. That is why, alongside suppression, a smoke control scenario is essential:
- Jet fan (impulse) systems — Ductless, ceiling-mounted fans push the smoke towards the exhaust points, controlling the evacuation direction and visibility; they are more flexible and economical than duct-based systems.
- Ducted mechanical smoke exhaust — Collects the smoke with exhaust ducts and fans and expels it outside.
What is critical is that the system automatically switches from the normal ventilation mode to the smoke exhaust mode during a fire; this transition is set up as a scenario integrated with the detection system.
Gas detection: CO and fuel gases
In enclosed car parks mechanical ventilation is mandatory — and what intelligently manages this ventilation is gas detection:
- Carbon monoxide (CO) detection — The CO produced by vehicle exhaust is a colourless, odourless, deadly gas. Rather than running the ventilation continuously at full power, CO detectors bring it into service in stages, when needed; this both protects life safety and lowers energy consumption.
- Fuel gas detection — LPG vehicles emit a gas that is heavier than air in a leak and collects on the floor; CNG/natural gas, on the other hand, is lighter than air and gathers at the ceiling. That is why detectors are placed at the correct level according to the character of the gas and catch a leak before it reaches the explosive limit.
Gas detection is the complement of fire detection: one catches the fire, the other catches the hazardous environment that could turn into a fire.
Fire detection: choosing the right detector for a car park
With the 1 July 2025 amendment, automatic fire detection is now mandatory in enclosed car parks. But there is a critical engineering decision here: which detector? The car park environment — exhaust smoke, tyre/brake dust, humidity and temperature fluctuations — misleads the ordinary optical (point) smoke detectors mounted on the ceiling and causes constant false alarms. And false alarms destroy the reliability of the system and the staff’s trust in it.
That is why heat-based and wide-area solutions are preferred in car parks:
- Linear heat detection cable — Detects a heat rise over a long distance; it is unaffected by dust and smoke, and pinpoints the location of the fire.
- Beam-type detector — Scans large open spaces with a beam of light between two points; it is economical for large car parks.
- Heat detectors — Trigger at a specific temperature threshold; because they operate on heat rather than smoke, they are reliable in the car park environment.
Choosing the right detector is the difference between “we installed it because it’s mandatory” and “a system that really works.”
Integrated scenario: everything works together
Car park fire safety is the work not of separately installed devices, but of layers that meet in a single scenario: gas detection manages the ventilation, fire detection catches the fire early, the dry pipe sprinkler (with an accelerator when needed) delivers water despite the freezing risk, and smoke control keeps the escape route open. When these are engineered together as a properly calculated whole, the car park is genuinely protected.
Summary
What makes a car park special is its unheated space: that is why a dry pipe sprinkler, not a wet one, is the right choice. In a dry system the water delay limits the zone size (≈2,840 L / 60 s water delivery requirement) and makes an accelerator essential in large systems. When you add exhaust smoke control, CO and fuel gas detection and car-park-appropriate heat-based fire detection, the protection made mandatory by 1 July 2025 becomes not just “present” but operational. You can review our car park solutions and contact us for a design tailored to your facility with a free site survey within Ankara.
This content is for informational purposes only. A binding, facility-specific assessment requires project-based work with a fire engineer.
© 2026 A-Pro Mühendislik. This is original technical content produced by A-Pro Engineering; all rights reserved. Copying, reproducing or republishing it in whole or in part without attribution and permission is prohibited.
Frequently asked questions
Why are dry pipe sprinklers used in a car park instead of wet pipe?+
Enclosed car parks are usually unheated; when the temperature drops below 0 °C, wet (water-filled) pipes freeze and the expanding water cracks the pipe and its connections. In a dry pipe system, the pipes are filled with pressurised air/nitrogen instead of water; the water waits behind the dry pipe valve in a heated valve room. When a sprinkler opens, the air is released, the valve opens, and water fills the pipe only at that moment. This eliminates the freezing risk.
Why is the zone (system) size limited in a dry pipe system?+
In a dry system, after a sprinkler opens the water must first sweep the air out of the pipes before arriving; this creates a delay. The larger the system, the longer the delay. That is why NFPA 13 limits the volume connected to a single dry pipe valve: if the system volume exceeds about 2,840 litres (750 gallons), it must be proven by calculation that water reaches the most remote point within 60 seconds. If this cannot be proven, the system is downsized or an accelerator is added.
What does an accelerator do, and when is it needed?+
An accelerator (quick-opening device, QOD) detects the pressure drop at the dry pipe valve early and opens the valve far faster than normal. This way water goes into service without waiting for the air to be released, and the water delivery time is shortened. In large-volume dry systems it becomes essential in practice (to meet the 60-second water delivery requirement).
Which fire detector is used in a car park?+
With the 1 July 2025 amendment, automatic fire detection is mandatory in enclosed car parks. However, exhaust smoke, dust and humidity mislead ordinary optical (point) smoke detectors mounted on the ceiling and produce false alarms. That is why heat-based solutions are preferred in car parks: linear heat detection cable, beam-type detector, or heat detectors. The choice is made according to the car park's geometry and ventilation.
Why is gas detection needed in a car park?+
Mechanical ventilation is mandatory in enclosed car parks; carbon monoxide (CO) detectors bring this ventilation into service in stages, when needed — providing both life safety and energy efficiency. In addition, gas detection for LPG (heavier than air, collects at floor level) and CNG (lighter than air, collects at the ceiling) vehicles catches a leak before it reaches an explosive level.
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