Planning can reduce chemical hazards.

Byline: GUEST VIEWPOINT By Paul Engelking For The Register-Guard

Nothing like a hydrogen leak to liven up your Monday morning. Most people aren't chemists, and don't know the exact hazards of molecular hydrogen. People might be interested in understanding the hazard it presents, and what they might do in case of exposure. Since the commercial use of molecular hydrogen is increasing with the growth of technology industries, the possibility of accidents like Monday's is rising in Oregon.

Oregon isn't new to hydrogen spills. Several years ago, a similar quantity of hydrogen was involved when a valve broke off a 5,000-gallon liquid hydrogen storage tank at a Tektronix plant to our north. But hydrogen leaks might be new to the Eugene-Springfield area.

Hydrogen is the lightest of elements. It forms a liquid if cooled to within 8 percent of absolute zero. This is what was being transported on Monday. Its principal hazard is the formation of an explosive vapor - hydrogen burns with the oxygen present in the air to form water, releasing great amounts of energy. A secondary hazard is related to hydrogen being extremely cold when liquefied. Additionally, liquid hydrogen is capable of creating extreme pressures as it warms, potentially bursting its container as it becomes gaseous. It poses a minimal chemical hazard.

Hydrogen and air mixtures are extremely sensitive to ignition, increasing its main hazard. Hydrogen can be ignited by the electrical brush discharges surrounding high voltage lines, or the little spark of a static electrical discharge from your finger touching a doorknob. Hydrogen flames can pass through smaller crevices than any other flames.

While most fuel vapors, such as gasoline, are flammable in mixtures between about 1 percent and maybe 5 percent fuel to air, hydrogen is ignitable in mixtures with air containing a few percent to as high as 75 percent hydrogen. By this measure, any hydrogen leak is potentially 10 times more susceptible to ignition than a hydrocarbon fuel leak. The flame velocity of hydrogen-air mixtures (about 11 meters per second) is an order of magnitude higher than that of gasoline vapors in air. This makes it much more likely to transition from subsonic flame to supersonic detonation, with the formation of shock waves travelling in excess of 300 meters per second.

Mixtures of hydrogen with air burn explosively. A well-mixed hydrogen-air explosion is capable of generating bulk pressures of 12 times ordinary atmospheric pressures, with even higher shock wave pressures possible. (Buildings can be destroyed by a doubling of atmospheric pressures, as occurs in tornadoes.)

Yet hydrogen poses very little chemical hazard. It is virtually nontoxic. Inhaled, it is harmful only to the extent that it might displace oxygen required for respiration. Since hydrogen gas is lighter than air, hydrogen vapors will rise. This makes a hydrogen spill more likely to dissipate rapidly, but also more susceptible to ignition from overhead sources of sparks, such as power lines. (One of the more bizarre aspects of Monday's incident is the driver's decision to stop his truck virtually beneath high-tension power lines that parallel Interstate 5.)

After a hydrogen accident, people should evacuate before the vapor arrives. No electrical equipment should be operated, including ordinary flashlights, unless it is certain that the equipment is certified "explosion proof." Vehicles should be used only if it is known that hydrogen is not immediately present.

If evacuation ahead of a hydrogen cloud is not possible, the second response should be to seek shelter-in-place within the most secure part of a building. (Baby-boomers can put their "duck and cover" civil defense training to good use.)

Emergencies involving hazardous materials should be thought through before they occur. A community can protect itself by rehearsal before hazardous events, and by limiting the number of scenarios that may occur. One way of doing this is by designating hazardous routes. In this manner, a community can focus its resources on a given hazardous materials problem in an organized way. Oregon communities are allowed by law to designate hazardous materials corridors if they comply with federal regulations.

The political will for addressing hazardous materials issues usually is a Johnny-come-lately affair, arising only after a disaster or near disaster has occurred. Designating local hazardous materials routes, for instance, has been rejected by one local mayor and one local legislator when the matter was brought to their attention by Eugene fire officials.

Inadvertent hazardous materials exposure has contributed to more American deaths than all acts of terrorism on U.S. soil, which may place the issue in perspective.

Paul Engelking of Lowell is a professor of chemistry at the University of Oregon.

CAPTION(S):

Emergency personnel line Highway 126 eastbound near Interstate 5 on Monday as they wait for a truck leaking liquid hydrogen to vent its load.