The immediate cause of the explosion was determined to be the
introduction of water to the molten sodium. Physical evidence confirmed
that the explosion occurred within the drum and did not involve the
material that had been spilled or the water under the floor grates. The
water is believed to have come from the shovel, which had been placed on
the wet floor grate. The moisture was transferred to the salt as it was
shoveled into the sodium drum.
Since sodium reacts violently with many substances, the contaminant
may have been something other than water. Even rust on the shovel could
cause a reaction; however, water is the most likely cause of the reaction.
The primary causal factor of this incident was the inappropriate
actions of employees at the H. C. Starck facility, trying to bum a much
larger heel of waste sodium than the normal operating procedure could
accommodate. In addition, the design of the drum cleaning area, to
include wet washing and sodium disposal in the same enclosure, created an
unnecessary hazard. The requirement to keep sodium away from any
potential source of moisture should have precluded conducting both of
these operations in the same space.
The documented procedure for burning small amounts of waste
sodium in the bottoms of drums appears to be reasonably safe, if all of the
steps are followed. The appropriate procedure for dealing with a larger
amount of residual sodium would be to maintain the argon in the empty
space above the sodium, reseal the drum, and return it to the supplier for
disposal or recycling. The lack of a documented procedure for dealing
with larger quantities created a situation where employees had to make a judgment that could not be based on experience or an appropriate risk
evaluation.
The company and the Newton Fire Department had done a good
job of working together to familiarize firefighters with the facility and to
inform them of the types of situations they might face at the plant. The
training, however, was directed toward small sodium spill fires that can
usually be handled with a relatively minor risk to personnel, as long as
basic safety precautions are followed and standard operating procedures
are employed. The dangers that were involved in this situation, with a
drum containing molten sodium, were far more severe than the Fire
Department or the company had anticipated. This situation shows how
training that deals with low risk situations can create a false sense of
security when the situation is more complex and dangerous.
If all of the information had been provided to the fire department,
including the significance of the quantity of sodium that was involved, the
fact that the sodium was in a molten state, and the presence of water in
the area, a thorough risk analysis could have been considered, prior to
formulating an action plan. The actual situation that was encountered was
an extremely high risk hazardous materials incident. The risk evaluation
would have revealed:
- The presence of burning molten sodium in the drum was a different
and much higher risk incident than previous training had
anticipated.
- There is no safe procedure available for a municipal fire department
to deal with a molten sodium fire, unless it has been previously
trained specifically for this type of situation and provided with
specialized equipment and protective clothing. Structural protective
clothing and self-contained breathing apparatus are inadequate
protection for the risk of being splashed with molten sodium or any
molten metal. There is no protective clothing designed to protect
the user from direct contact with burning molten sodium.
- The possible extinguishment alternatives for molten sodium are very
limited: blanketing the molten sodium with an inert gas or covering
it with soda ash. In either case, the extinguishing agent, if available,
would have to be applied very gently and carefully to float on top of
the molten metal surface. It may also have been feasible to smother
the fire with a lid that completely covered the opening, if one had
been available. However, all of these possibilities would expose
firefighters to excessive risk. The potential consequences of an
error in the extinguishing procedure are extreme.
- In the worst case scenario, if the container had failed, the molten
sodium could have flowed through the grates and into the water
containing troughs, resulting in an immediate explosion, probably of
equal or greater magnitude to the explosion that did occur. The fire
was burning in an isolated room, designed to contain an explosion.
If no one had been in the immediate area when the explosion
occurred, there would have been no injuries and the damage would
have been about the same as actually occurred, which was minor. If
the doors to the room had been closed even less damage would
have occurred.
Weighing the alternatives that were available to the Newton Fire
Department, a thorough risk evaluation would suggest taking no action on
this fire. The risks involved in taking action are very high, while the
consequences of not fighting the fire are relatively minor. The fire
probably would have continued to bum, producing smoke, until the
material was fully consumed. In all probability, the steel drum would not
have failed and the fire would have terminated when the fuel was
consumed.
The post incident evaluation suggests that a decision to not fight the
fire would have been the best decision. However, it was very difficult to
recognize these factors at the time, based on the information that was
available to the Incident Commander and the other firefighters. Their
training had not prepared them for the situation they encountered,
although they were much better informed and trained than most municipal
firefighters on dealing with sodium fires. They had been trained to handle
a less hazardous situation and had not been trained or given the
information that would have caused them to recognize the higher risk
situation.
The failure to establish an effective liaison with knowledgeable plant
employees caused decisions to be made before all of the information could
be gathered, assembled, and analyzed. Instead of one primary liaison
contact between the fire department and a responsible individual for the
plant, several different fire department members had contact with several
different plant employees, which increased the level of confusion.
The interviews with injured fire department members indicate that
the crews did not have a good appreciation of the nature of the situation
before they went in to attempt extinguishment. The smoke filled
atmosphere made it difficult to size-up the situation; however, they were
guided by the plant workers’ confirmation that they should use salt as an
extinguishing agent. They did not have a more specific plan of action to
establish what they would do after entering the fire area.
Less than ten minutes elapsed from the arrival of the first
companies until the explosion occurred. This suggests that very little time
was taken for evaluation of the situation and formulation of a plan. This
indicates that the approach was very action oriented, when the actual
situation should have called for careful analysis before, or instead of, taking
action.
The delay that occurred in contacting the EMS units to come in and
treat the injured firefighters indicated a deficiency in an otherwise good
standard operating procedure. Having EMS units respond and stage at a
safe distance from the incident is a good plan for hazardous materials
incidents, particularly when the EMS providers are not trained or equipped
to operate in a dangerous area. The weakness in the plan was the inability
to make contact between the Incident Commander and the EMS supervisor
when the ambulances were needed at a specific location. The delay of
several minutes caused an extremely high level of anxiety, although it does
not appear to have had significant consequences on the outcome of the
incident; the paramedics did not have any better treatment capability for
the burned firefighters than was already being attempted and faster
transportation would have made little difference in the outcome.
Note: The communications problem between the Fire Incident Commander
and the ambulances has already been corrected by changing the standard
operating procedure. The ambulance crews had been provided with an
additional radio to maintain contact with the Fire Incident Commander.
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