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 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.

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

      o     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.)

      o     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.

      o     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.

      o     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.

      o     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.

      o     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.

.
.