CNG Cylinder Safety: Checks Every Car Owner Should Do

To keep a CNG car safe, have the cylinder, valve, pipes and fittings inspected by an OGRA-authorised workshop, make sure the cylinder is within its re-testing date, and act at once if you smell gas. If you suspect a leak, stop the car somewhere open, switch off the engine and the CNG valve, get everyone out, keep away from flames and sparks, and have the system checked before you use gas again.

CNG kits are fitted to a large number of cars, vans and pickups in Pakistan. A properly fitted, tested cylinder is designed to be very strong; investigations of CNG fires and explosions in Pakistan have repeatedly pointed to substandard cylinders and kits, poor fitting and leaks from high-pressure pipes and connections rather than the cylinder simply failing. That means most of the risk is in things owners can check.

Who regulates CNG kits

The Oil and Gas Regulatory Authority (OGRA) regulates CNG in Pakistan, including approved cylinders, kits and the workshops that fit and test them. Rules on re-testing intervals, approved equipment and where CNG may be used, for example restrictions on CNG cylinders in public service vehicles, have been tightened over the years. Ask an OGRA-authorised workshop for the current requirements for your vehicle, and check OGRA's latest notices rather than relying on old advice.

What to check on your cylinder

• Manufacturing and test dates: every approved cylinder carries markings showing when it was made and tested. Make sure it is within its re-testing date.
• Certification: the cylinder should be an approved type, fitted by an authorised workshop, with the paperwork to show it.
• Mounting: the cylinder must be held firmly with proper brackets and bolts to the car's body, not strapped loosely in the boot. In a collision, a loose cylinder becomes a heavy projectile.
• Condition: look for dents, deep scratches, rust or signs of heat damage on the cylinder.
• Valve: the cylinder valve should be in good condition, with no hissing, corrosion or damage.
• Ventilation: in hatchbacks and sedans, the valve area should be vented outside the cabin, as originally fitted.

Pipes, fittings and the kit

The high-pressure pipe that runs from the cylinder to the engine bay, and the fittings at each end, are where leaks most commonly start. Vibration, rust and poor installation can loosen or crack them over time.

• Ask the workshop to leak-test all joints and fittings during each inspection.
• Check that the pipe is clipped securely along the underbody and is not rubbing against sharp edges or hot exhaust parts.
• Make sure the reducer and solenoid valves in the engine bay are securely mounted and the wiring is tidy.
• Never let anyone repair a high-pressure line with tape, sealant or improvised fittings.

Signs of a gas leak

• A smell of gas inside or around the car. Natural gas is given an added odour so that leaks can be smelled.
• A hissing sound from the boot, under the car or the engine bay.
• The CNG gauge falling unusually fast, even when the car is parked.
• Rough running or stalling when switched to CNG.

Leaks are more dangerous in winter, when windows stay closed and gas can build up inside the cabin. Even a small spark from a switch, a lighter or a cigarette can ignite it.

What to do if you smell gas

• Pull over somewhere open and away from traffic, buildings and other cars if you can.
• Switch off the engine and the ignition. Do not operate other electrical switches more than you have to.
• Close the cylinder valve if you know how and can reach it safely.
• Get everyone out and move well away from the car.
• Do not smoke, light anything or use a lighter to look for the leak.
• If there is a strong smell, hissing or any sign of fire, call Rescue 1122 and keep people away.
• Do not drive the car on CNG again until a qualified workshop has found and fixed the leak.

Safe habits at the filling station

• Switch off the engine and get all passengers out of the car before filling begins.
• Do not smoke or use a lighter anywhere near the station.
• Watch for any hissing or smell during filling and tell the attendant at once.
• Do not let the station overfill or bypass safety equipment.

CNG and breakdowns

Many CNG-related breakdowns are not dangerous; they are simply cars that run out of gas or run poorly on CNG. CNG stations in some areas have faced supply cuts in winter in past years, and long queues are common when gas is available. Keep enough petrol in the tank to switch over and reach a station or your destination. Running a car on CNG for long periods with an almost empty petrol tank is also hard on the electric fuel pump, which relies on fuel for cooling.

If your car breaks down and it has a CNG kit, tell the recovery service when you call. A recovery crew will want to make sure the cylinder valve is closed before moving the car, and a car that has been in a collision with a CNG cylinder in the boot needs careful handling. After a rear-end collision, have the cylinder mounting, valve and pipes inspected before using CNG again, even if there is no visible damage.

A simple CNG safety routine

• Know the test date on your cylinder and diarise the next re-test.
• Have the kit leak-tested at an authorised workshop regularly, and after any accident.
• Keep the cylinder area of the boot clear, so the valve is easy to reach and see.
• Treat any smell of gas as an emergency, not an inconvenience.
• Keep Rescue 1122 and a recovery service number saved in your phone.