Hydrogen is an important chemical commodity. It has been mass-produced for more than 50 years, and in the U.S. alone, more than eight million tons are produced annually, mostly by steam reforming of natural gas. NASA was the first to use fuel cells powered by hydrogen as a dependable source of both electric power and potable water on manned missions, and today, hydrogen is routinely transported safely both as a cryogenic liquid and as a compressed gas by rail, barge, truck and pipeline for use in the aerospace, food, petrochemical and semiconductor industries. These industries have an excellent safety record with hydrogen because they understand the risks and how to manage them.
Hydrogen has a low ignition energy-as little as 0.017 millijoules at 30% concentration, in contrast to 0.25 millijoules for other hydrocarbon fuels. However, at their lower flammability limits, methane and hydrogen have very similar ignition energies of about 10 millijoules.
|Properties of Hydrogen|
|Lower Flammability Limit (%) ||4||5.3||1,7||1,3|
|Lower Detonation Limit (%) ||18.3 ||6,3 ||3,1 ||1,1|
|Upper Detonation Limit (%) ||59||13.5||9.2||3.3|
|Upper Flammability Limit (%) ||75||17||10.9||6.0 |
|Auto Ignition Temperature ||585 C||537 C||450 C||215 C|
|Minimum Ignition Energy||0.017 mL||0.274 mJ||0.240 mJ||0.240 mJ|
SETTING THE RECORD STRAIGHT Today, most people take for granted their use of hydrocarbon fuels such as gasoline, propane and natural gas yet an 1875 report by the U.S. Congressional Horseless Carriage Committee warned that stores of gasoline hurtling down the street at 15 miles per hour would constitute a fire and explosive hazard of the first rank.2 Tens of millions of people now pump gasoline into their cars each day.
Natural gas and propane are commonly piped into homes for use in appliances such as water heaters, stoves, and furnaces. The risks associated with the use of these fuels are accepted because systems that use them achieve sufficient levels of safety.
Hydrogen as a fuel is a new idea for most people, but its use dates back to the 19th century. In the United States, "town gas" was used to light city streets and was piped into homes to fuel lamps, cooking stoves and gas heaters. Town gas was produced from coal and contained about 50% hydrogen along with methane, carbon dioxide and carbon monoxide. Town gas is still used safely today in parts of Japan, China and other Asian countries.