Specific Gravity - Blue Bird Q - BUS Owner's Manual

NOTE: The tanks are full at 3000 psi or 3600 psi and 70 degrees Fahrenheit. The pressure will vary with
temperature. Decreasing with lower temperature and increasing with higher temperatures. Filling appara-
tus compensates for the temperature effect.
WARNING: Never fill to more than permissible pressure. Contact the manufacturer if an accidental
overfill occurs.
NOTE: The fuel level is only accurate for tanks that are open. For example, if one tank is open and reads 1000
psi, then the fuel available to the engine is proportionate to the total capacity.

SPECIFIC GRAVITY

The specific gravity of natural gas relative to air (air=1.00) is 0.56 to 0.62 depending on gas composition.
This indicates that natural gas is lighter than air. In the event of a natural gas leak, the gas will rise and
dissipate given open conditions. There is no possibility of CNG accumulating in pools on the ground beneath
a spill.
NOTE: Natural gas odorants allow its detection by humans before dangerous concentrations are reached.
In the case of LNG releases, the cold vapor initially released is heavier than the surrounding warmer air
and thus stays low, near the ground (a visible vapor cloud is often formed from the condensation of water in
the cold air-gas mixture). As the vapor cloud warms, it will increase in volume, become lighter than air, and
rapidly dissipate.
FUEL TOXICITY AND SAFETY
Natural gas is a nontoxic gas. It is flammable under proper conditions. Additionally, it can cause suffoca-
tion if enough oxygen is displaced. LNG has the added safety concern of being a cold (-260
pressure. Severe frostbite may occur from contact with LNG or associated cold components. Furthermore,
many common materials change their strength characteristics when exposed to LNG temperatures, thus pre-
senting additional hazards.
WARNING: LNG tanks have the potential for explosions under circumstances such as those described
for LPG explosions.
Although natural gas has odorants to aid in detection of leaks, these odorants are removed during lique-
faction, thus LNG vapors can not be detected by smell. (NOTE: LNG odorants have been developed but are
not commonly used due to the relatively restricted use of LNG at this time).
FLAMMABILITY
Autoignition temperature for natural gas at atmospheric pressure is 1004
temperature range of 442 to 880
presence of an ignition source exists when the ratio of air to fuel is within flammability limits (i.e., fuel can not
ignite if it is mixed with too much or too little oxygen). The flammability limits for natural gas are 5.3 to 15%
volume of gas in air. For comparison, the flammability limits of unleaded gasoline are 1 to 7.6% volume of
gasoline in air. As a practical matter, there is no oxygen present in CNG cylinders or LNG tanks, therefore
ignition within the cylinder or tank is not possible. In the event of fuel leak, there will be a small area in which
the air to fuel ratio is within the flammability limits. In a closed garage, or within the passenger compart-
ment, ignition conditions are more likely to be met. Odorants used in CNG allow its detection before the
lower flammability limit has been reached.
o F for gasoline and approximately 500
44
o F compared to an autoignition
o F for diesel fuel. The risk of fire in the
o F) liquid under