Department of Energy, EH&S Bulletin

EH-92-2

Implosions Under Negative Pressure

ENVIRONMENT, SAFETY & HEALTH BULLETIN

Assistant Secretary for U. S. Department of Energy

Environment, Safety & Health Washington, D.C. 20585

DOE/EH-0248 Issue No. 92-2 August 1992

IMPLOSIONS UNDER NEGATIVE PRESSURE

Several recent incidents at Department of Energy (DOE) facilities were the result of implosions (an inwardly directed explosion) in DOE laboratories. Implosions in laboratory facilities may occur when vacuum pumps, or other equipment that creates negative pressure, are used in conjunction with glass laboratory containers, such as Dewar flasks,

or when such equipment is used in the vicinity of glass windows and [sic] viewpoints. Although the force of an implosion is directed inward, glass fragments may be propelled in all directions. In addition to the cuts these fragments may inflict, they may imbed in the flesh and, in the process, inject toxic, corrosive, or irritant products into the body.

Several of the implosion-related incidents that have occurred at DOE, as well as recommended actions to ensure worker safety, are discussed below. Improper Selection of Glass Containers Contributes to Incidents When laboratory work requires a procedure involving a vacuum, the use of round-bottomed flasks is preferable. In two recent incidents, selecting the wrong container for a procedure that involved a vacuum contributed to the resulting implosion. In one DOE laboratory, a chemist received superficial chemical burns to the face when an implosion occurred during the routine preparation of an acrylic acid compound. At the time of the incident, the chemist was removing oxygen from a glass flask in which he had been collecting a filtered solution of water and sodium hydroxide. Shortly after the chemist began the evacuation process, the bottle imploded, projecting its contents onto his face and clothing. Fortunately, the chemist was wearing safety glasses and protective clothing, and his burns were only superficial. During their investigation into the incident, investigators found that when collecting the water/sodium hydroxide solution, the chemist substituted a 4-liter Erlenmeyer flask for the 1-liter, vacuum-filter flask called for in the laboratory's procedures. However, the flask the chemist substituted was structurally incapable of withstanding the pressure of a vacuum.

In a similar incident at another DOE facility, a worker was evacuating a 6-liter glass bottle that contained 3 liters of acrylamide in water. About a minute after the evacuation process began, the bottle imploded, dispersing acrylamide solution throughout the room. Injury was prevented only because the worker was not directly in the path of the bottle. In this incident, the worker selected an "aspirator" bottle, which is a cylindrical, flat-bottomed bottle with a narrow neck and a glass hose fitting near the bottom. This type of bottle is not designed to withstand a high vacuum.

Glass Windows/Viewports/Panels Implode Windows, glass viewports, and other glass components and equipment found in a laboratory are also vulnerable to implosion when under negative pressure. A laboratory worker at one DOE facility, for example, was injured while trying to locate a vacuum leak. The worker was kneeling across a component being used in an experiment when the glass viewport of the component imploded, then exploded, and sent glass fragments in the worker's abdomen. It is believed that there may have been a structural weakness in the glass and that this weakness, combined with pressure from the worker's body, caused the implosion. To avoid similar incidents in this laboratory, the glass viewport in the component was replaced with a plastic one.

In a second implosion-related incident, an undiscovered leak in the glovebox atmosphere sampling line created an excessive vacuum within the glovebox and resulted in the implosion of the front glass panel of the glovebox. This incident was finally traced to failure to install an "oil bubbler" (i.e., a pressure-relief device) designed by the glovebox manufacturer. The purpose of the oil bubbler is to draw room atmosphere into the glovebox to relieve excess vacuum or let air escape to relieve excess pressure. Had the device been installed, the implosion would have been prevented.

Shielding in the Laboratory Enhances Worker Safety

The use of appropriate shielding is essential when working with materials that may either implode of explode. Adequate shielding is essential to worker safety in such cases, because it provides a barrier between the worker and glass fragments.

One method of shielding that is effective when the potential for either an implosion or explosion exists is the use of a laboratory fume hood. Conducting experiments inside the hood with the vertical sash lowered provides protection from flying glass on all four sides of the experiment and contains any potentially hazardous or toxic substances should an explosion or implosion occur. In addition, in a November 1989, Safety Note, "Glass Containers Shatter During Experiments with Volatile Materials" (DOE/EH-0119), the Office of Environment, Safety and Health offered recommendations for appropriate shielding of laboratory personnel whose work requires handling explosive or energetic materials.

The shielding information in this publication, which was taken from the DOE Explosives Safety Manual, Chapter 11, Section 21 (page II-67), is currently being updated. For additional information on shielding, refer to the Manual or call Gerald Meyers at (301)903-3190. Recommendations

The potential for an implosion that results in injury to laboratory personnel exists in any DOE facility where vacuum pumps are used in the presence of glass. Laboratory procedures and practices should be reviewed and revised as necessary to reduce this potential risk to worker safety.

Maintain equipment in good working order, with all safety systems installed.

Use filament tape on Dewars, cold taps, and thermos bottles to restrain fragments in case of implosion, unless an oxidizing gas such as oxygen or ozone is being stored. (Organic wrappings that contain volatile plasticizers or adhesives may ignite when the flask is used with an oxidizing gas.)

Conduct experiments that have the potential for resulting in an explosion or implosion inside a laboratory fume hood with the vertical sash closed and the exhaust system turned on to ensure that glass fragments and/or toxic or hazardous substances are contained.

Replace glass containers with plastic wherever possible. Polycarbonate (Lexan) is preferable over acrylic (Lucite or Plexiglas) as it is considerably less combustible. Use only borosilicate glass when flame or heat will be applied to the container.

Ensure that laboratory procedures specifically state the type of container to be used and monitor employees to ascertain that they are using the containers described.

Use safety goggles and other appropriate protective equipment, such as face shields and protective clothing, when conducting laboratory procedures that require the use of vacuum pumps or other equipment that creates negative pressure.

Provide regular training in basic laboratory safety practices, and stress the necessity of wearing appropriate protective equipment and clothing.

This Bulletin is one in a series of publications issued by EH to share occupational safety information throughout the DOE complex. To be added to the Distribution List or to obtain copies of the publication, call (615)576-3482. For additional information regarding the publications, call Barbara Bowers, Safety Performance Indicator Division, Office of Environment, Safety and Health, U.S. Department of Energy, Washington DC 20585, (301)903-3016.