Case Studies of Confined Space Incidents by NIOSH

Preventing Occupational Fatalities in Confined Spaces

BACKGROUND

The deaths of workers in confined spaces constitute a recurring occupational tragedy; approximately 60% of these fatalities have involved would-be rescuers. If you are required to work in a:
   SEPTIC TANK            SILO            REACTION VESSEL
   SEWAGE DIGESTER        VAT             BOILER
   PUMPING/LIFT STATION   DUCT            PIPELINE
   SEWAGE DISTRIBUTION    UTILITY VAULT   PIT
     or HOLDING TANK   
                                                                                                                                                              
or similar type of structure or enclosure, you are working in a CONFINED SPACE.

 

CASE REPORTS OF FATAL INCIDENTS

Case #1 - RECOGNITION AND RESCUE (FATALITIES = 1 WORKER + 1 RESCUER)

A a 54-year-old worker died inside a floating cover of a sewage digester while attempting to restart a propane heater that was being used to warm the outside of the sewage digester cover prior to painting it Workers had wired the safety valve open so that the flow of propane would be constant, even if the flame went out. The heater was located near an opening in the cover of the digester. When the worker attempted to restart the heater, an explosion occurred that vented through the opening. The worker crawled away from the heater into an area that was oxygen deficient and died. A co-worker attempted a rescue and also died.

Case #2 - RECOGNITION AND RESCUE (FATALITIES = 1 WORKER + 1 RESCUER)

A 20-year-old construction worker died while attempting to refuel a gasoline engine powered pump used to remove waste water from a 66 inch diameter sewer line that was under construction. The pump was approximately 3,000 feet from where the worker had entered the line. The worker was overcome by carbon monoxide. A co-worker, who had also entered the sewer line, escaped. A 28-year-old state inspector entered from another point along the sewer line and died in a rescue attempt. Both deaths were due to carbon monoxide intoxication. In addition to the fatalities, 30 firefighters and 8 construction workers were treated for carbon monoxide exposure.

Case #3 - RECOGNITION AND RESCUE (FATALITIES = 2 RESCUERS)

Two workers (26 and 27 years old) were overcome by gas vapors and drowned after rescuing a third worker from a fracturing tank at a natural gas well. The tank contained a mixture of mud, water, and natural gas. The first worker had been attempting to move a hose from the tank to another tank. The hose was secured by a chain and when the worker moved the hose, the chain fell into the tank. The worker entered the tank to retrieve the chain and was overcome.

Case #4 - RECOGNITION AND RESCUE (FATALITIES = 1 WORKER + 1 RESCUER)

A 22-year-old worker died inside a toluene storage tank that was 10 feet in diameter and 20 feet high while attempting to clean the tank. The worker entered the tank through the 16 inch diameter top opening using a 1/2 inch rope for descent. Although a self-contained breathing apparatus was present, the worker was not wearing it when he entered the tank. The worker was overcome and collapsed onto the floor the tank. In an attempt to rescue the worker, fire department personnel began cutting an opening into the side of the tank. The tank exploded, killing a 32-year-old firefighter and injuring 15 others.

Case #5 - RECOGNITION AND RESCUE (FATALITIES = 1 WORKER + 1 RESCUER)

A 21-year-old worker died inside a waste water holding tank that was four feet in diameter and eight feet deep while attempting to clean and repair a drain line. Sulfuric acid was used to unclog a floor drain leading into the holding tank. The worker collapsed and fell face down into six inches of water in the bottom of the tank. A second 21-year-old worker attempted a rescue and was also overcome and collapsed. The first worker was pronounced dead at the scene and the second worker died two weeks later. Cause of death was attributed to asphyxiation by methane gas. Sulfuric acid vapors may have also contributed to the cause of death.

Case #6 - RECOGNITION AND RESCUE (FATALITY = 1 RESCUER)

A 43-year-old father died while attempting to rescue his 28-year-old son from a tank used to store spent acids from a metal pickling process. The tank was out of service so that sludge could be removed from the bottom. The son collapsed in the tank. The father attempted a rescue and also collapsed. The two were removed from the tank; the son was revived, but the father died. The cause of death is unknown.

Case #7 - RECOGNITION (FATALITY = 1 WORKER)

A crew foreman became ill and was hospitalized after using an epoxy coating, which contained 2-nitropropane and coal tar pitch, to coat a valve on an underground waterline. The valve was located in an enclosed service vault (12' x 15' x 15'). The worker was released from the hospital on July 3, 1985, but was readmitted on July 6, 1985; he lapsed into a coma and died on July 12, 1985, as a result of acute liver failure induced by inhalation of 2-nitropropane and coal tar pitch vapors. A co-worker was also hospitalized, but did not die.

Case #8 - RECOGNITION AND RESCUE (FATALITIES = 1 WORKER + 3 RESCUERS)

A 27-year-old sewer worker entered an underground pumping station (8' x 8' x 7') via a fixed ladder inside a three foot diameter shaft. Because the work crew was unaware of procedures to isolate the work area and ensure that the pump had been bypassed, the transfer line was still under pressure. Therefore, when the workers removed the bolts from an inspection plate that covered a check valve, the force of the waste water blew the inspection plate off, allowing sewage to flood the chamber, and trapping one of the workers. A co-worker, a supervisor, and a policeman attempted a rescue and died. The first two deaths appeared to be due to drowning and the latter two appeared to be due to asphyxiation as a result of inhalation of "sewer gas.

 

CONCLUSIONS

The case studies described above are summarized in Table 1:

_________________________________________________________________________________________________________                                                           _______DEATHS_______
CASE   DATE       TYPE OF SPACE         TYPE OF HAZARD   WORKER RESCUER TOTAL  COMMENT
_________________________________________________________________________________________________________
#1   12/29/83   Sewage digester       Oxygen deficiency    1     1       2      ---

#2     3/8/84   Sewer line            Toxic atmosphere;    1     1       2    38 others injured
                construction          physical hazard

#3    10/4/84   Fracturing tank       Oxygen deficiency    0     2       2    2 rescuers drowned

#4    12/5/84   Toluene storage tank  Toxic atmosphere;    1     1       2    15 others injured
                                      explosion; limited 
                                      entry and exit

#5    5/13/85   Waste water tank      Toxic atmosphere;    1      1      2    Rescuer died two weeks
                physical hazard                                                  later

#6     6/7/85   "Spent" acid          Toxic atmosphere     0      1      1    Rescuer was father of
                storage tank                                                     worker

#7     7/2/85   Underground           Toxic atmosphere     1      0     1     Worker died of acute
                waterline, valve area                                            liver failure;
                                                                                 another worker ill
                                                                                 but recovered

#8     7/2/85  Sewage pumping         Physical hazard;     1       3     4    2 died of drowning; 
               station                toxic atmosphere                          2 of asphyxiation
_________________________________________________________________________________________________________
                                              TOTALS       6       10   16    53 OTHERS INJURED
_________________________________________________________________________________________________________

Based on the information derived from these case studies, NIOSH concluded that these fatalities occurred as a result of encountering one or more of the following potential hazards:

In each of these cases there was a lack of RECOGNITION and TESTING, EVALUATION, and MONITORING prior to entry nor had a well-planned RESCUE been attempted.

These incident reports suggest that RECOGNITION of what is a confined space in conjunction with the proper TESTING, EVALUATION, and MONITORING of the atmosphere and development of appropriate RESCUE procedures could prevent such deaths. These three steps are discussed below.

NIOSH investigations indicate that workers usually do not RECOGNIZE that they are working in a confined space and that they may encounter unforeseen hazards. TESTING and EVALUATION of the atmosphere are typically not initiated prior to entry and MONITORING is not performed during the confined space work procedures. RESCUE is seldom planned and usually consists of spontaneous reaction in an emergency situation.

RECOMMENDATIONS

In light of findings to date regarding occupational deaths in confined spaces, NIOSH recommends that managers, supervisors, and workers be made familiar with the following three steps:

1. RECOGNITION

Worker training is essential to the RECOGNITION of what constitutes a confined space and the hazards that may be encountered in them. This training should stress that death to the worker is the likely outcome if proper precautions are not taken before entry is made.

2. TESTING, EVALUATION, AND MONITORING

All confined spaces should be TESTED by a qualified person before entry to determine whether the confined space atmosphere is safe for entry. Tests should be made for oxygen level, flammability, and known or suspected toxic substances. EVALUATION of the confined space should consider the following:

The confined space should be continuously MONITORED to determine whether the sphere has changed due to the work being performed.

3. RESCUE

RESCUE procedures should be established before entry and should be specific for each type of confined space. A standby person should be assigned for each entry where warranted. The standby person should be equipped with rescue equipment including a safety line attached to the worker in the confined space, self-contained breathing apparatus, protective clothing, boots, etc. The standby person should use this attached safety line to help rescue the worker. The rescue procedures should be practiced frequently enough to provide a level of proficiency that eliminates life-threatening rescue attempts and ensures an efficient and calm response to any emergency.

 

 



NIOSH ALERT: January 1986

DHHS (NIOSH) Publication No. 86-110

NIOSH has published the following documents which contain further information:

Criteria for a Recommended Standard .... Working in Confined Spaces, DHEW Publication No. 80-106.

Guidelines for Controlling Hazardous Energy During Maintenance and Servicing, DHHS Publication No. 83-125.