Confined Space Incident Kills Two Workers - Company Employee and Rescuing Fireman
The National Institute for Occupational Safety and Health (NIOSH), Division of Safety Research (DSR) is currently conducting the Fatal Accident Circumstances and Epidemiology (FACE) Project, which is focusing primarily on selected electrically-related fatal Injuries and confined space fatalities. By scientifically collecting data from a sample of fatal accidents, the FACE will identify and rank factors which Increase the risk of fatal injuries for selected employees.
On November 15, 1984, one worker died after entering a toluene storage tank. During the rescue attempt, a fireman was killed when the tank exploded.
The Division of Safety Research received an invitation from Arizona’s Industrial Commission, Division of Occupational Safety and Health to include this confined space Incident In our FACE project. A research team consisting of the project. officer, the section chief, a safety engineer, an occupational health nurse, and an observer from another NIOSH division visited the Division of Occupational Safety and’ Health (DOSH), the Fire Department, and the site of the fatality. Pictures (35mm and videotapes) of the event, prior to, during and after the explosion were available from the fire department, DOSH, and local television stations. Multiple Interviews were hold, survey instruments were completed, and next-of-kin Interviews wore done, one with the assistance of an interpreter.
Synopsis of Events
The owner of a bulk petroleum storage facility discovered that the toluene storage tank (10 ft. in diameter and 20 ft. in height) was contaminated and would have to be drained and cleaned. Since the tank’s only access portal was located on top of the upright cylindrical tank, the owner decided to have a clean-out access portal installed at the bottom of the tank when emptied. A contractor was called to provide cost estimates for installing the portal. The contractor performed & site survey, of the tank and told the owner that the tank must be drained, all sludge removed, and be thoroughly ventilated before he would install the portal. The owner directed his maintenance supervisor to get the tank prepared-for the contractors
On the day of the Incident the supervisor and an unskilled laborer (a San Salvadoran immigrant on his first day back on the job after working another job for approximately 2 months) drained the tank to its lowest level–leaving 2 to 3 inches of sludge and toluene In the bottom–and prepared for a dry run of entry into the tank via the top access portal.
The supervisor rented a self-contained breathing apparatus (SCBA) from a local rental store and Instructed the laborer in use of the SCBA and in the procedure they intended to follow. Since a ladder would not fit Into the 16-inch diameter access holes the supervisor secured a knotted, 1/4-inch rope to the vent pipe an top of the tank and lowered the rope Into the hole. The 16-inch diameter opening on the top of the tank was not large enough to permit the laborer to enter wearing the SCBA. Therefore, it was decided the SCBA would be loosely strapped to the laborer so it could be held over his head until he cleared the opening. once entry had been made, the supervisor was to lower the SCBA onto the laborer’s back so it could be properly secured.
Immediately prior to the Incident, both employees were on top of the tank. The laborer was sitting at the edge of the opening. The supervisor turned to pick up the SCBA. While he was picking up the unit, he hoard the laborer In the tank. He turned and looked into the opening and saw the laborer standing at the bottom of the tank. He told the laborer to come out of the tank, but there was no response. The supervisor bumped the rope against the laborer”s chest attempting to got his attention. The laborer was mumbling. but was still not responding to his supervisor’s commands. At this point, the supervisor pulled the rope out of the tank, tied the SCBA to it and lowered the unit into the tank. Again, he, yelled to the laborer in the tank, bumped him with the unit and told him to put the mask on. There was still no response. The laborer fell to his knees, then fell onto his back, and continued to mumble. At this point, the supervisor told the facility manager (who was on the ground) to call the fire department.
The first call went to the police department who relayed It to the fire department. Included in the fire department response was the hazardous materials team, due to the information received about the material in the tank.
The fire department (including the rescue and the hazardous materials teams) arrived an the scene approximately 10 minutes after the Initial notification. After.appraising the situation, fire officials decided to implement a rescue procedure rather than a hazardous materials procedure. Therefore, removal of the person ‘down’ inside the tank was given top priority.
The 16-inch diameter opening at the top of the tank was not large enough to lower a fireman domed in full rescue gear. Therefore it was decided to cut through the side of the tank to remove the victim. The firemen were aware of the contents of the tank (toluene) and the possibility of an explosion.
The procedure developed by the fire department involved making two 19-inch vertical, cuts and a 19-inch horizontal cut with a gasoline powered disc saw. After the cuts were completed, the steel flap would be pulled down and the victim removed.
While the hazardous materials team was cutting, other fireman were spraying water on the saw from the exterior to quench sparks. Two other fireman were spraying water on the interior cut from the top opening. Three fireman with the hazardous materials team were doing the actual cutting; they were alternately operating the saw because of the of fort required to cut through the 1/4-inch thick steel. Sometime during the horizontal cut a decision was made to bring the two firemen off of the top, which meant no water spray on the interior. Simultaneously, the exterior water spray was removed to put out flammable liquid residue burning an the ground as a result of the shower of sparks from the saw. Thus, at the precise time of the explosion, no water was being sprayed an the saw/cut from exterior or interior; both vertical cuts were completed and the horizontal cut was 95% complete when the explosion occurred.
One fireman was killed Instantly from the explosion and several were Injured. The man inside the tank was presumed to be already dead at the time of the explosion.
The conclusions and recommendations are presented In two parts: Part I the confined space entry; and Part 11 – the rescue effort.
Part I – Confined Space Entry
The following factors may have contributed to the confined space fatality:
1) The company had no confined space entry procedures.
2) The supervisor was not qualified to direct confined space entry.
3) The laborer was Inadequately trained for confined space entry – possible language barrier.
4) Appropriate protective clothing and equipment were not provided.
5) The only access portal required vertical entry.
6) The access portal was small.
7) It was the laborer’s first day back on the job. (He may have felt obligated-to perform any task assigned.)
1) Written confined space entry procedures should be developed and used.
Procedure should contain the following: permit system, testing and
monitoring of the atmosphere training of employees, safety
equipment/clothing. safe work practices, rescue procedures, standby
person requirements. and use of respiratory protection.
2) Selection of proper respiratory protection – whether it be a
self-contained breathing apparatus (SCBA) or supplied air system – is
essential. Selection should be determined by the physical limitations,
equipment available, and work procedures.
3) Confined space testing and evaluation by a qualified person before entry
and implementation of safety measures will help reduce risk taking by
4) Vertical access f ran the top of a 201 tank by a rope was found to be
physically impossible while wearing respiratory. protection and protective
clothing. An additional access port on the side near ground level would
eliminate this problem. The port should be of adequate size to permit
entry of a worker wearing full protective clothing.
5) Workers must be properly trained (in English, Spanish, or the prevailing
language) in confined space entry procedures and use of personal
protective equipment Also, the tank contents and known potential hazards
should be discussed.
6) A prior accident should have alerted someone that additional protection
was needed. If entry procedures are being followed and an accident
occurs, it is necessary to re-evaluate the procedures and make necessary
corrections-for employee safety.
Part II The Rescue Effort
The following factors may have contributed to the rescue effort fatality and
1) The condition of the person down inside the tank was not known.
2) The location and size of the only access portal on the tank precluded
entry by a rescuer wearing full protective clothing and equipment.
3) The fire department’s confined space entry procedures precluded entry
into a confined space containing hazardous materials without full
protective clothing and equipment.
4) The choice of methods to open the tank for rescue entry introduced an ignition source to an atmosphere which was known to be potentially explosive (see tank calculations).
5) The use of water sprays to prevent ignition of a flammable/explosive atmosphere In a confined space may not be effective under certain conditions.
6) There were combustible materials an the ground surrounding the tank which ignited prior to the explosion and necessitated removal of exterior water spray sway from saw/cut.
7) The fire department chain of command possibly created confusion when orders were given without full knowledge of the situation.
8) The number of fire department personnel in the immediate area may have been excessive.
9) The victim (firefighter) was directly in front of the cut during the cutting procedure and when the explosion occurred.
1. While cutting the tank and assisting follow firemen who were cutting, one firefighter stood directly in front of the opening, rather than to the side. This maximized the impact the victim received from the explosion. It Is recommended that procedures be outlined that minimize such risk by firemen.
2. When hazardous tasks are performed only essential personnel should be In the immediate area, regardless of perceived risk by fIrefighters. Nonessential personnel should be permitted only after the hazardous task(s) has been completed.
3. More extensive departmental procedures for efforts Involving responses to explosive environments and hazardous materials are needed. Procedures should include command responsibilities, determinations of and distinctions between rescue and recovery efforts, uses of potential sources of ignition, methods to minimize risks of ignition, etc.
4. City fire departments should establish a registry of confined spaces and toxic/explosive substances for specific companies within the area in which they serve. Such a registry should provide not only the name of the substance, but should also provide sufficient Information so that emergency response personnel will have one comprehensive source that provides information sufficient to safely effect a rescue effort.
5. Research is needed to determine the best methods (if any) to gain entry in such circumstances. Cutting may be too hazardous, even with the use of water sprays.
Simple calculations based upon the geometry of the tank involved MA the chemical and physic” properties of toluene were made to answer questions as to the potential flammability of the tank’s atmosphere.
Toluene ‘Us a sufficient vapor pressure that, given ordinary temperatures, pressures, time and sufficient toluene,. it can- saturate the atmosphere in an .enclosed space to flammable concentrations in air. In fact,, the saturated concentration Ls approximately midway La the flammable range.
Saturated Concentration a Vapor Pressure X 1316 gm mmHg
Vapor Pressure = 36.7 mmHg Toluene 30 degree C
36.7 X 1316 48297 ppa
4.8 % (Saturation within flammable range)
Lower Flammable Limit (LFL) Toluene = 1.2% Upper Flammable Limit (UFL) Toluene = 7.1%
Based upon a nominal tank volume of some 10,000 gallons, it would require only 56 ounces of toluene to raise the concentration to the lower flammable limit in air, and hence, into flammable atmosphere
Tank Volume = 10,000 gallons (g)
10000 g X 1 cuft = 1333 cuft 7.5g
LFL Toluene = 1.2%
Volume of Vapor a 0.012 X 1333 cuft
a 16 cuft
Amount of-Toluene to Evolve 16 cuft Vapor
1 Pt a 16 oz
16 ox. of toluene will occupy 4.6 cuft
16 cuft X 16 oz 55.6 oz 4.6 cuft
This amount of toluene, less than one half of a gallon. if spread over a flak surface equivalent to the area of the tank bottom. would Only occupy a depth of less than one hundredth Of an inch (0-01″).
Tank Diameter 9’7″ a 115″
Area of Tank PI r^2 / (D/2)^2 Batton
3.1416 X 2 2
56 as toluene I 1.8 cuin 101 Cuin 1 ox
depth liquid toluene
a depth sqin
10, cuin 9.7 X 10 -3 inch 10387 sqin
Observation of any toluene covering the bottom of a tank of these dimensions indicates an amount of toluene sufficient to produce a flammable atmosphere given enough time and the right conditions (time and temperature).
To surpass the 4.8% saturation concentration In the tank, it would require a temperature Increase. At 38.00 C the vapor concentration would exceed the UFL of 7.1%. However, the ambient temperature at 1500 hours on November 15, 1984, was 240 C, which kept the atmosphere In the tank in the explosive range (approximately 3.5%).