Discuss the safety issue while using CNG and LPG as fuels. 4
Answers
It comes as a surprise to many to hear that natural gas is one of the safest transport fuels available. Natural gas is a naturally occurring product, consisting mainly of methane (approx. 90%).
In its natural state, natural gas is odourless. As a safety measure, the gas is odorised prior to distribution to provide a ready means of leak detection. An average person can easily detect the smell of gas at a concentration as low as 0.3% by volume in air. That concentration is about 16 times lower than the level which will support combustion.
Natural gas requires a concentration of between 5% and 15% in air for combustion to occur, meaning in most cases the smell of gas would be detected well before combustion conditions are met. These are the upper and lower flammability limits of the fuel. Natural gas also has a high ignition temperature, about 600 degrees Celsius, compared with about 315o C for gasoline (1110o F).
Natural gas has no known toxic or chronic physiological effects (i.e. it is not poisonous). Exposure to a moderate concentration may result in a headache or similar symptoms due to oxygen deprivation but it is likely that the smell would be detected well in advance of concentrations being high enough for this to occur.
The fact that natural gas is lighter than air further enhances its safety. Unlike other fuels such as diesel, petrol or LPG, which are heavier than air, should a natural gas leak occur, the gas will readily dissipate into the atmosphere. This eliminates the risk of the fuel accumulating or pooling at ground level and causing a greater risk or hazard.