Onboard Fire Extinguisher

1. Definition and Regulatory Requirements

An onboard fire extinguisher is a portable fire extinguishing device kept inside a motor vehicle to put out early-stage vehicle fires. Its core function is to allow drivers and passengers to quickly suppress a blaze before it spreads during initial emergencies—such as electrical short circuits, fuel leaks, or an overheating engine bay emitting smoke—buying critical time for occupants to evacuate safely and for emergency services to arrive.
Under China's "Road Traffic Safety Law" and the "Technical Specifications for Safety of Power-driven Vehicles Operating on Roads" (GB 7258-2017), buses, coaches, and hazardous goods transport vehicles must be equipped with fire extinguishers. While not legally mandatory for private passenger cars, carrying one on board is strongly recommended for safety. Certain local jurisdictions (such as Shenzhen) have already made fire extinguishers mandatory for all passenger cars, where non-compliance can result in warnings or fines.

2. Type Selection and Applicable Fire Classes

Vehicle fire extinguishers must be selected based on the specific types of fires that may occur in a motor vehicle. These typically fall into the following classes:

Class A (Combustible solids) : Seat fabrics, interior plastics, sound-deadening materials, etc.
Class B (Flammable liquids) : Fuel, engine oil, brake fluid, etc.
Class E (Electrical fires) : Wiring harness insulation, electronic components, traction batteries, and other live electrical equipment.

Extinguisher Type	Applicable Fire Classes	Advantages	Disadvantages
Dry Powder Fire Extinguisher (ABC Class)	Classes A, B, C, and E (Electrical)	Broad application coverage, affordable, high fire knockdown efficiency	Discharges a powdery cloud that can corrode electrical components and is difficult to clean up afterwards
Water-Based Fire Extinguisher (Re-ignition Resistant)	Class A (Solids) and selected Class B (Flammable liquids)	Clean discharge, leaves no powdery residue, strong re-ignition suppression	Not suitable for live electrical equipment (risk of electric shock); requires anti-freeze protection in sub-zero climates
Carbon Dioxide (CO2) Fire Extinguisher	Classes B, C, and E (Electrical)	Leaves zero residue, non-conductive, non-corrosive to components	Extremely low discharge temperature (-70°C) with risk of frostbite on contact; poses an asphyxiation hazard at extinguishing concentrations, requiring good ventilation

Selection Recommendations:

For standard petrol or diesel passenger cars, ABC dry powder fire extinguishers are the default choice (highly versatile and cost-effective), with an optimal capacity of 1kg to 2kg.
For battery electric vehicles (BEVs) and plug-in hybrid vehicles (PHEVs), dry powder fire extinguishers can be used to contain cabin fires and external electrical fires. However, note that dry powder is completely ineffective against battery thermal runaway; it serves only to suppress surrounding combustible materials.
Water-based extinguishers are well-suited for Class A cabin interior fires and leave minimal mess, but a safe distance must be maintained from live electrical components.

3. Capacity Specifications and Storage Locations

Vehicle Type	Recommended Capacity	Fire Rating	Discharge Duration (Approx.)
Compact Cars / Sedans	1kg	2A 55B C E	8–10 seconds
Mid-size Sedans / SUVs	2kg	3A 70B C E	12–16 seconds
Large SUVs / MPVs / Light Commercial Vans	3–4kg	4A 90B C E	20–30 seconds

Key Points for Storage Locations:

The ideal spot is underneath the driver's seat or alongside the front passenger seat—ensuring the driver can grab it single-handedly from the seat, saving vital seconds without having to step out and rummage around.
The next best option is the boot side net pocket or next to the spare tyre well, provided it is securely tethered to prevent it from rolling around and causing hazards on the move.
Never bury it deep in the boot beneath luggage where it cannot be accessed quickly in an emergency.
Avoid prolonged exposure to direct sunlight inside a hot boot during peak heat (temperatures can exceed 60°C). While units certified to national standards will not explode under normal ambient heat, sustained high temperatures accelerate seal ageing; opt for a model rated for wider operating temperatures.
The extinguisher must be secured in a dedicated mounting bracket to prevent it from becoming a dangerous projectile during hard braking or a collision.

4. Usage Instructions and Key Operational Points

Operating Acronym (PASS) :
1. P (Pull) : Pull the safety pin (the metal pin or plastic tamper seal on the handle).
2. A (Aim) : Aim the nozzle at the base of the fire (the lowest combustion point), not at the leaping flames above.
3. S (Squeeze) : Squeeze the operating lever firmly to start spraying.
4. S (Sweep) : Sweep the nozzle from side to side across the base of the fire until the flames are fully extinguished.
Tackling Engine Bay Fires in ICE Vehicles:
Never pop and lift the bonnet fully open immediately—the sudden rush of fresh air will cause an instant flashover. The correct procedure is: pop the bonnet release to its first safety catch (leaving a 10–15 cm gap) , insert the extinguisher nozzle into the opening, and spray directly at the base of the fire. If the fire shows no sign of abating within 1 minute, evacuate to a safe distance immediately and wait for emergency services.
Tackling Cabin Interior Fires:
If the fire starts around the centre console, seats, or floor mats, discharge the extinguisher from outside through an open door to avoid inhaling toxic fumes inside the enclosed cabin. If the fire has already engulfed the dashboard, do not attempt to salvage personal belongings; evacuate immediately.
Tackling EV Battery Fires:
Dry powder extinguishers are completely ineffective against lithium-ion battery thermal runaway and can only be used to put out secondary fires on tyres, body panels, or interior trim. If the underbody battery pack begins smoking or jetting flames, retreat to a safe distance of at least 15 metres, call 119 immediately, and leave it to the fire department to cool down the battery pack using continuous, heavy volumes of water or foam.

5. Routine Inspection and Maintenance

Inspection Item	Frequency	Pass Standard	Action Required on Failure
Pressure Gauge Reading	Monthly	Needle points within the green zone	If in the red (under-pressurised) or yellow (over-pressurised) zone, send for inspection or replace immediately
Physical Condition	Monthly	Cylinder free from corrosion or dents, nozzle clear of blockages, safety pin intact	Must be replaced if damaged or clogged
Weight Check	Every six months	Weighed on scales; extinguishing agent loss does not exceed 5%	Must be serviced or replaced if loss exceeds 5%
Service Life	Per manufacturer label	Dry powder extinguishers generally have a valid lifespan of 5–10 years (inspected every 2 years after 5 years from manufacture)	Expired units must be sent to a qualified service centre for recertification or disposal

Maintenance Points:

Fire extinguishers should be kept away from damp, excessively hot, or corrosive environments; ideal storage temperatures range between -20°C and +55°C.
Once discharged (regardless of how little was used), the unit must be sent to an authorised fire safety specialist for refilling; never attempt to dismantle it yourself.
Decommissioned or expired extinguishers must never be discarded in ordinary waste bins (they remain pressurised vessels); hand them over to a certified fire equipment dealer or hazardous waste recycling centre for proper disposal.

6. Common Mistakes and Unsafe Practices

Incorrect Practice	Consequences	Correct Procedure
Burying the extinguisher under piles of boot luggage	Cannot be retrieved quickly during an emergency	Secure beneath the driver's seat or in a dedicated side net for instant access
Storing the extinguisher horizontally or upside down	Dry powder settles and cakes, clogging the nozzle and causing discharge failure	Always keep it mounted upright
Assuming it is ready for use without checking the pressure gauge	Discharge will be weak if under-pressurised, failing to suppress the blaze	Inspect the pressure gauge needle position every month
Attempting to fight a fire when flames are already too high	Delays evacuation, exposing oneself to severe burn injuries	Evacuate immediately if flames exceed 30 cm and cannot be suppressed within 1 minute
Dousing an engine bay fire with plain water	Water spatters burning oil, spreading the blaze and posing electrocution risks	Use an approved automotive fire extinguisher only

7. Future Trends

Automated Aerosol Fire Extinguishing Devices: Compact, maintenance-free automatic fire suppression modules are making inroads into passenger vehicles. Triggered by heat-sensing cords, they automatically discharge ultra-fine aerosol extinguishing agents the moment engine bay temperatures breach a calibrated threshold—requiring zero driver intervention and suppressing early fires before the driver even spots the smoke.
Perfluorohexanone (FK-5-1-12) Extinguishers: A next-generation clean agent that offers exceptional fire knockdown without residue, electrical conductivity, or corrosive damage to sensitive electronics. It is ideal for high-tech EVs and connected vehicles; although pricier than dry powder, it is increasingly being adopted as factory equipment in premium models.
Smart Pressure Monitoring Modules: Smart extinguishers equipped with Bluetooth or NFC connectivity allow drivers to check pressure readings and expiry dates directly via a smartphone app. Automatic push notifications alert owners when service or replacement is due, eliminating failures caused by overlooked inspections.
Fire Suppression Linked with E-Call: High-end models are increasingly integrating engine bay thermal and smoke sensors directly into the vehicle's onboard network. When abnormal temperature spikes are detected, the system can automatically trigger the suppression module while simultaneously relaying the vehicle's coordinates and fault status to emergency services via E-Call, providing a seamless "detect-suppress-alert" safety net.