CNG tanks are much stronger than liquid fuel tanks (petrol, diesel or LPG) and far exceed the impact and flammability standards laid down by the strictest international standards.
In the event of an accident, a fire is caused in bi-fuel vehicles by the petrol tank rupturing and not by the CNG cylinder rupturing, which is the strongest component in the car.
Each natural gas cylinder is tested at a pressure of 300 bar, which is 1.5 volts above the normal operating pressure (200 bar).
They are also tested at destructive hydraulic pressure; the minimum strength required is 2.25 times the operating pressure (450 bar), although in practice rupture pressures of 580 bar are reached. Finally, for cylinder rupture dynamics, strict international standards require a behaviour known as "leak before burst", i.e. a progressive leakage of gas from cracks in the cylindrical body before the structure fails.
Fusible safety valves, finally, in the event of fire and an increase in temperature and pressure, then allow the controlled escape of gas, avoiding overpressure.
In the event that the on-board piping should break, the overflow safety valve (located on the cylinder valve) prevents uncontrolled gas release.
All these tests of thermal and mechanical resistance mean that CNG cylinders are by far the strongest components on board the vehicle, including structural parts.
