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Safety Issues of Compressed Hydrogen
General Characteristics of Hydrogen
Hydrogen is a gas with the smallest molecular weight of all gasses. It is colorless, odorless, tasteless,
and noncorrosive with combustibility and fast diffusivity. It needs to be handled with caution.
However, hydrogen is not dangerous in any other way and could even be less dangerous than other
fuels in some aspects. Since hydrogen is the lightest element , it rapidly rises and disperses in the
atmosphere without mixing with the air. Hydrogen is relatively safe as it does not easily reach the
concentration for explosion.
Hydrogen Gas Features
A hydrogen gas leak should be prevented to minimize the
hazard of ignition or detonation.
The followings are properties of gaseous hydrogen.
▪It has the lowest molecular weight, and is the smallest
molecule of any element.
▪It has the lowest density and the highest buoyancy of
any element.
▪It can cause brittleness in some materials, including
metals (materials chosen for hydrogen applications
are not susceptible to brittleness).
▪ It is colorless, odorless and tasteless.
▪ It burns invisibly and without smoke.
▪It has the lowest ignition energy of any fuel (less than
one-tenth that of other fuels).
▪ It has a wide flammability concentration range of 4% to 75%
Hydrogen Gas Leak Detection System
The hydrogen gas detection sensor detects a hydrogen leak. If there is a leak, the hydrogen storage
system and electrical systems will be shut down. Sensors will illuminate a waring light when
concentrations reach the minimum flammability limit of hydrogen.
Sensors are installed at the fuel cell stack, fuel suppling system, and in between the hydrogen
storage tank and the ceiling of vehicle. These sensors detect a hydrogen leak under emergency
situations, allowing the system to block the hydrogen.
Diffusion Velocity Ratio of Diffusion and
Flow in the air
CH
Gas
4
Diffusion
1.0
Turbulent
1.0
Flow
3
C
H
H
3
8
2
0.63
3.8
0.6
2.83
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