No. 473 June 1998

U.S. Department of Health and Human Services

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

The Explosion Hazard From Hydrogen Gas Generation

Inside Sealed Frames

Background

The National Institute for Occupational Safety and Health

(NIOSH) recently investigated ignition incidents resulting from

drilling holes into sealed and filled plow frame sections. A

farmer and farm worker were seriously burned in two separate

incidents that occurred in the same county in New York under

similar conditions. They had just penetrated sealed sections of

their plow frames with electric drills when a roar of escaping gas

at high pressure was heard, and the victims were thrown back by

the gas jet and engulfed in flames. The flames were quickly

extinguished, but the victims suffered burns. NIOSH experts

were asked to help find the cause of these hazardous incidents.

Approach

Inspection of the frame sections involved in the incidents

showed no discoloration, charring, or blistering of paint in the immediate vicinity of the holes. Probing the holes with a

magnetized blade revealed a hard interior fill material and the

presence of some metal punchings. This fill material was more

extensively sampled from another section that had been cut

through (figure 1). This revealed a wide range of metal

punchings that was used as ballast in these steel frame sections,

which had been welded shut after the filling operation. The

punchings were found to consist of various forms of steel (carbon,

galvanized, and stainless) and other metals, including titanium.

Sealing the holes and sampling the gases present revealed the

depletion of oxygen from the original air atmosphere and the

presence of hydrogen. The hydrogen concentration was found to

increase with time under sealed conditions. The pressure in the

resealed sections also increased with time at a steady

rate. A safe method of drilling into an intact sealed section was

found and was used to determine the gas pressure and composition in this section. This gas was nearly pure hydrogen at an

absolute pressure of 185 psi, or over 12 times atmospheric

pressure.

Results

The mechanism for the generation of hydrogen has not been

definitively proven; however, all available evidence points to an

electrochemical reaction involving metals of substantially

different activity and electrical potential in the presence of water

and oxygen. The oxygen helps provide the relatively high voltage

needed to decompose water to hydrogen and hydroxide ion in

conjunction with an active metal such as zinc (the coating in

galvanized steel) or possibly aluminum. The origin of the water

is believed to be an oil/water emulsion that is used as a cutting

fluid in machine shops. Only a few tenths of a percent of water

in the steel scrap can account for the hydrogen pressures that have

been found in frame sections. To date, only metal-filled frame

sections have shown evidence of gas formation. However, the

possibility exists for the formation of hydrogen from a sealed

hollow frame if acidic conditions exist in the section from an

acidic flux used in fabrication or from bacterial action. Bacterial

action can also produce methane under anaerobic conditions,

which was found in one of the frames investigated.

Recommendations

Clearly, the presence of a highly flammable gas such as

hydrogen at high pressures inside a simple plow frame is both a

serious and unsuspected hazard. When such a frame is penetrated

by an electric drill or by an acetylene torch, that gas will be

released a s
Figure 1.CMetal fill from exposed section of plow frame.

a powerful jet that will entrain air and be easily ignited by the

electric motor or torch flame. The public must therefore be

alerted to the potential hazard of drilling or cutting into sealed

frame sections on farm equipment and other equipment frames,

particularly if the frame has been filled. Signs or lights should be

attached to the equipment only with built-in or clamped mounting

brackets or other nonpenetrating devices.

Eliminating this hazard will require more stringent control

over the ballast material used to fill the frames to ensure that

internal gas is not produced or that expansion of the fill does not

rupture the frame upon strong heating, as in a welding operation.

Under present circumstances, manufacturers should limit their

metal scrap fill material to ordinary steel similar in composition

to the steel frame; small vent holes should be provided to

eliminate the possibility of gas pressure buildup inside the sealed

sections.

For More Information

For more information on these findings and how to prevent

this explosion hazard, contact Isaac A. Zlochower, Ph.D., NIOSH

Pittsburgh Research Laboratory, Cochrans Mill Rd., P.O. Box

18070, Pittsburgh, PA 15236-0070, phone: (412) 892-4276, fax:

(412) 892-6595, e-mail: iaz0@cdc.gov

To receive other information about occupational safety and

health problems, call 1-800-35-NIOSH (1-800-356-4674),

or visit the NIOSH Home Page on the World Wide Web at

http://www.cdc.gov/niosh

Mention of any company name or product does not constitute endorsement by the National Institute for Occupational

Safety and Health.