Yes, it is safe. The properties of CNG make it a safe fuel. It is lighter than air, so in case of a leak it just rises up and disperses into the atmosphere. Besides, a high auto-ignition temperature of 540 degrees centigrade as against petrol’s 360 degrees centigrade, makes it a safe fuel. Also, in case of a leak, if CNG’s concentration in the air is less than 5% or more than 15%, the gas will not burn even in the presence of a spark.