One of the critical issues with the use of hydrogen is safety. Contrary to popular perception, hydrogen is less flammable than gasoline and other fossil fuels. Like any other fuel, hydrogen has risks if not properly stored or transported. However, the transportation of hydrogen at very high pressure, or very low temperature, brings other hazards. These hazards can be controlled through the use of proper handling and controls.

The reputation of hydrogen as unsafe has been unfairly tainted by the Hindenberg incident and the hydrogen bomb. Investigation into the Hindenberg incident proved that the aluminum power-filled paint varnish that coated the ship started the fire—not the hydrogen. Since hydrogen is a small molecule, it has a tendency to escape through small openings more so than other gaseous or liquid fuels. Hydrogen will tend to leak through holes or joints of low pressure fuel lines only 1.26 to 2.8 times faster than a natural gas leak through the same hole. Natural gas has an energy density three times greater than hydrogen, so a natural gas leak results in a greater energy release than a hydrogen leak. If a hydrogen leak occurs, hydrogen disperses much more quickly than other fuels. Hydrogen is lighter and more diffusive than gasoline, propane, or natural gas. If an explosion occurred, hydrogen has the lowest explosive energy per unit of stored fuel.

Liquid hydrogen has a different set of safety issues. If liquid hydrogen spills, there could be burns associated with it. Liquid hydrogen has characteristics similar to an oil spill, but it dissipates rapidly. If a pressure valve fails, an explosion could occur because of the liquid rapidly turning into vapor. This can be prevented by putting the correct controls and valves into the hydrogen system.

When hydrogen is aboard a vehicle, the potential dangers include explosion and toxicity. Hydrogen as a source of fire can occur from fuel storage or the fuel cell itself. The fuel cell has the lowest hazard. Small amounts of hydrogen and oxygen exist in the fuel cell, which are separated by a thin polymer membrane. If the membrane ruptures, the fuel cell would immediately lose its potential, and the control system could disconnect the supply lines. When designing hydrogen systems, several factors need to be considered:

• A catastrophic rupture due to a defect in the tank or puncture by a sharp object.
• A large leak due to faulty controls or a puncture.
• A slow leak due to stress cracks in the tank liner, or pressure relief valve.

These failure modes can be prevented in many ways. They include the following:

• Leak prevention through thorough testing of tanks and equipment.
• Installing more than one valve.
• Designing equipment for shocks, vibrations, and wide temperature ranges.
• Adding hydrogen sensors or leak detectors.
• Ignition prevention by illuminating a source of electrical sparks.
• Designing fuel cell supply lines that are physically separated from other equipment.

In order for hydrogen to become widely accepted, international regulations codes and standards need to be developed for construction, maintenance, and operation of hydrogen facilities and equipment. Uniformity of safety requirements will increase customer confidence in using hydrogen.

Send Page To a Friend

Rate this article: