Page 22 - Introduction to Transfer Phenomena in PEM Fuel Cells

Introduction to Hydrogen Technology 11
1.1.3.2. Flammability risk
When a hydrogen layer is formed, the risk of flammability is significantly
higher than for a slick of gasoline or natural gas. The energy required to
ignite it is about 10 times lower than for natural gas.
1.1.3.3. Risk of formation of an explosive layer
Hydrogen disperses faster than traditional fuels. It is diluted four times
faster in air than natural gas and 12 times faster than gasoline vapors. This
volatility is a protective factor, limiting the formation of hydrogen layers.

Remember that hydrogen is used in industry. Prevention methods make it
possible to limit the risks, such as the addition of an inert gas (such as CO 2)
to reduce the flammability of hydrogen.

The use of a ventilation system and the deliberate ignition of hydrogen
also prevent the formation of an explosive layer. If regulation is applied in
an industrial environment, it still has to be defined for hydrogen consumer
applications.

Safety measures would guarantee its use, particularly in the case of
hydrogen vehicles and distribution infrastructure.

1.1.4. Advantages and challenges to raise

Here are some advantages and some challenges to raise, which are
considered as downfalls for the use of hydrogen as an energy vector [AUP 13].

1.1.4.1. Advantages
There are six advantages:

– high energy molecule (120 MJ/kg vs. 50 MJ/kg for methane);
– neither pollutant nor toxic;
– its combustion in air generates only water;

– it is the lightest gas (wide diffusion in air = safety);
– it is easy to transport (pipes);

– depending on its mode of production: reduction of emissions, in
particular CO 2.