Investigators learned that the construction subcontractor was preparing a sewer tap for the radiological monitoring bioassay laboratory construction project.  The backhoe operator snagged the 480-volt line while removing material during a hand-digging operation to locate identified interference.  No workers were injured during the incident.  Investigators determined that contractor personnel used ground penetrating radar to confirm marks installed by surveyors to locate known interferences within the buffer and excavation areas identified on drawings.  Figure 1 shows the result of  the ground penetrating radar survey.   Known interferences are those reflected on the controlled record drawings.  The buffer establishes the exploration limits where the ground penetrating radar is used to confirm known interferences and identify unmarked interferences.

The ground penetrating radar indicated an interference paralleling the curb in the area located on the controlled drawings where the 480-volt electrical line was identified.  Sewer lines were also noted both paralleling the road and perpendicular to the road.  Another interference was confirmed beside the manhole within the excavation area limits.  The contractor initiated hand digging to locate only the interference identified beside the manhole.  The other interferences discovered didn’t conflict with his scope of work.  The operator removed accumulated material from the excavation with a rubber tire backhoe until the excavation deepened to the point where the operator snagged the 480-volt line.

Local site utilities personnel, brought in after the cut cable was discovered, used a radio frequency signal to confirm the “as found condition” and the “as designed condition” shown on Figure 1. 

The manhole in the drawing was installed during the original sewer project for the site.  Four different subcontracts as well as the facility’s own work processes may have been responsible for laying and not recording the location of the subject cable.  Investigators suggest a configuration management problem because of a previous cut in this 480-volt line several years ago when another sewer tap was made.  The facility contractor apparently cut the cable and repaired the damaged cable by routing the new conductor around the manhole. The contractor apparently made no changes to the site drawings following this work.  Excavation for the manhole and subsequent electrical installation excavation made it difficult to see the 480-volt line routed around the manhole, because ground penetrating radar could not see through the disturbed earth and barriers.

EH engineers identified the following similar events involving cutting buried electrical cables.
 

 KEYWORDS: electrical, cable, backhoe

 FUNCTIONAL AREAS: Construction, Configuration Management, Industrial Safety
 
 

Investigators identified other recent events where the subcontractor failed to follow procedures, perform post maintenance, or apply quality assurance measures.  On August 23, 1999, a work control representative reported that a wire rope inspection for a 24-ton crane had not been performed within the required surveillance period.  The crane was used on three occasions after the August inspection date had passed.  This event stemmed from failure to follow established procedures.  
(ORPS Report RL--PHMC-SNF-1999-0023)

On September 23, 1999, also at this facility, craft personnel failed to recognize potential load limits for basin grating while they moved an equipment cart containing rigging and a hydraulic drive unit weighing approximately 1,400 lbs.  This event also stemmed from personnel not properly following established procedures  (ORPS Report. RL-PHMC-SNF-1999-0028).  The similarity in corrective actions among many events at this facility seems to indicate that there may be a systemic, recurring procedure problem. 

EH engineers identified the following similar event involving procedure problems.
 

• Operating Experience Summary 98-17 reported that on April 13, 1998, at the Rocky Flats Environmental Technology Plutonium and Processing Facility, an electrical arc occurred inside an enriched uranium decontamination activities glovebox because a process specialist failed to follow a procedure requiring power to be turned off. Investigators believe the arc occurred as the process specialist was lifting the lid for the decontamination fixture and it, or some of the material being processed, contacted energized electrodes in the glovebox. The specialist believed she received a shock because she felt heat and experienced a slight tingling in her arm. A qualified procedure verifier secured the power to the electrodes. An assisting radiation control technician instructed the specialist to sit down, checked the area for contamination, and notified the foreman. Medical personnel determined that no injury occurred and that the specialist was probably not shocked. The facility manager directed facility personnel to apply a lockout/tagout to the system to preserve the scene for further investigation. 

(ORPS Report RFO--KHLL-PUFAB-1998-0028)

KEYWORDS: procedures

FUNCTIONAL AREAS: Procedures, Management, Training and Qualification
 
 

The dryer is a part of the breathing air purifier and consists of two desiccant-filled vessels (or towers).  One vessel on line dries the incoming air going to the breathing system, while a non-heated air purge regenerates the second vessel.  An electrically operated (solenoid) purge valve on the on-line vessel opens and reduces pressure at 5 minute intervals as a part of drying process.  This causes shuttle valves to divert the incoming air to the opposite vessel.  When the desiccant tower changes from the on-line to the purge position, the solenoid purge valve opens, allowing rapid venting of the stored air.  This causes an air cannon effect with a sonic boom, resulting from a rush of air mass from the bottom of the tower.  The muffler (or silencer) is mounted on the outlet of the purge valves to dampen the noise.   It is designed to slow, disperse and dampen the air pressure impulse, which otherwise occurs when the air jet exits the pipe and undergoes a sudden expansion to atmosphere.

The failed silencer on the left in Figure 2-1, and the filter with pressure relief, Figure 2-2, are manufactured by Atomuffler.  The silencer is a cylinderical device made from treated paper filter media rolled into layers with an outer metal protective shell.  The desiccated air inside the unit escapes from the outlet side of the air dryer after passing  through the muffling process.  Investigators determined that the incoming air picked up desiccating dust, which tended to clog the filter media.

Figure 2-1      Failed Silencer without Pressure Relief Valve
 

Figure 2-2 Silencer with Spring-loaded Pressure Relief Valve
 

This restricted the flow of air, causing a backpressure on the on-coming purged air, resulting in an “air hammer” effect.  The air hammer fatigued the filter media over time, and eventually caused it to fail.  The investigators also determined that the failed device was lacking the following design features recommended by the manufacturer:

• Modified Filter Media- lining the inside of the muffler, to capture desiccant fines without significantly impeding the airflow.
• Orifice- provided at the inlet of the silencer, chokes the flow of air, limiting the magnitude of the air delivered and reducing “air hammer” effect.
• Pressure-actuated diversion valve or pressure relief valve, relieving static pressure above 13 psig.

These recommendations could have prevented a build up of excessive pressure in the breathing air system and consequent rupture of the filter media.  Investigators discovered that another similar silencer equipped with a spring-loaded pressure relief device, Figure 2-2,  performed its function without failure.  Provision of  a spring-loaded pressure-relief valve prevented air impulse damage on the muffler by diverting excess airflow.  Investigators also determined that regular inspections and maintenance of the breathing air system would have helped line management to mitigate conditions contributing to the failure. 

EH has reported a number of similar events involving near miss situations.  The following are some examples.
 

• OE Summary 99-15 reported that on April 12, 1999, the health and safety manager for the Grand Junction Projects Office, Monticello Project, reported that a 1,000-gallon diesel fuel tank had suffered structural damage when it was over-pressurized during refueling.  Because the fuel tank did not have adequate venting capacity, pressure built up, deforming the tank and launching the fuel nozzle approximately 15 feet into the air.  As a result, 10 gallons of diesel fuel spilled, most of which remained inside a spill containment berm.  The fuel vendor had supplied the diesel fuel tank and a 2,000-gallon gasoline tank to support Monticello project subcontractor operations.  Improperly vented tanks can result in tank failure, release of tank contents, and personnel injury.  (ORPS Report ALO--MCTC-GJPOTAR-1999-0001)

These events underscore the importance of proper design of components of operating systems and their timely preventive maintenance to ensure personnel safety.  The following directives and standards provide guidance for developing design changes and system modifications of existing systems for improved and safer operations.
 

• DOE O 6430.1A, General Design Criteria, can be accessed from DOE Directives Home Page at http://www.explorer.doe.gov.
• DOE-STD-1073-93, Part 1 and Part 2 Guide for OperationalConfiguration Program can be accessed at http://.tis.eh.doe.gov/techstds

KEYWORDS: design deficiency, filter, muffler

FUNCTIONAL AREAS: Design Modifications, Preventive Maintenance
 
 

The crane is a Grove 90-Ton Rough Terrain Hydraulic Crane.  It is one of four portable, heavy capacity cranes used for lifting at the Site.  All four cranes, three 90-ton and one 80-ton, are 13 to 15 years old and are now cycling through annual inspections.  The design life of these cranes is 10 years.  Investigators determined that the cracked welds on the 15-year-old crane were identified during a load test portion of the inspection and cracked welds caused a deflection of the crane’s boom.  Investigators also found similar cracked welds during their inspections of the other three heavy capacity cranes, although none of those deficiencies caused a deflection of the crane boom during load testing.  The cause of the cracked welds has not yet been determined, but investigators suspect that metal fatigue is a contributing factor.

The DOE-SR also owns a number of 22-ton and 40- to 45-ton rough terrain cranes.  Investigators inspected a sampling of these smaller cranes, following the discovery of the weld cracks in the large cranes, and found no cracked welds.  Most of these cranes are also manufactured by Grove Crane.  All of the 40-to 45-ton rough terrain cranes are currently being inspected in connection with this problem.  The cranes are generally the same age as the four 80-and 90-ton cranes, but have different configurations. 

Local representatives of Grove Crane inspected the cracked welds on the subject crane and investigators expect that Grove factory representatives will also inspect the other cranes.  Grove Crane had supplied inspection criteria for use in annual inspections, but these were not instrumental in identifying the cracked welds.  The manufacturer has made suggestions for repairing the damaged welds, however, there has been no determination whether the damage is so severe that it is irreparable.  If the initial inspected crane were to be scrapped and replaced the cost could range from  $500,000 to $1 million. 

Facility management plans to involve their quality assurance organization in resolving this problem.  They have also contacted the DOE Hoisting and Rigging Topical Committee and the manufacturer, Grove Crane, to obtain information on incidence of cracked welds on similar pieces of equipment.  Facility management stated that a sound engineering basis will be employed should the cracked welds be repaired and the crane returned to service.

Facility managers, maintenance, and quality assurance personnel should review the following references, which provide guidance and good practices applicable to the current issue (i.e., Quality Assurance, testing, surveillance).
 

• DOE-STD-1090-99, Hoisting and Rigging, provides guidance for hoisting and rigging and identifies related codes, standards, and regulations.
• American Society of Mechanical Engineers ASME Standard B-30.5-1994, applies to the construction, installation, operation, inspection, and maintenance of jacks; power-operated cranes, monorails, and crane runways; power-operated and manually-operated derricks and hoists; lifting devices, hooks, and slings; and cableways.  ASME B 30.5-1994, along with specific Grove Crane criteria, provides the primary basis for the annual inspection where the cracked welds were identified.

KEYWORDS: rough terrain crane, cracked welds

FUNCTIONAL AREAS: Construction, Maintenance, Industrial Safety
 
 

Investigators determined that the fan supplies air to various offices in an administration building and that it had malfunctioned during the night.  Pieces of the fan wheel were scattered around the fan room.  Investigators determined that the end wheel of a multiple wheel squirrel cage belt-driven fan had rotated off its shaft, contacted the housing, and broke in pieces.  The investigators also found that the housing had dislodged from its mountings and was resting on the fan drive shaft.  They also determined that the fan motor had tripped on over-current due to friction caused by the dislodged fan-housing rubbing on the fan shaft.  At this point in the investigation the cause of the dislodged fan housing is unknown.  The fan and motor assembly are over 43 years old and the estimated cost to replace them is approximately $10,000. 

Investigators determined that during maintenance on the fan, a bearing had been replaced because of vibration.  Investigators have also determined that a design change had been applied to the unit, which raised the airflow.  The increased airflow was below the system high limit setting and was verified as safe.  Investigators determined that there was no visible vibration associated with this higher flow.  The unit was hard anchored and no vibration isolators were used on the fan-housing portion of the unit. 

KEYWORDS: bearing, HVAC fans, maintenance

FUNCTIONAL AREAS: Mechanical, Malfunction
 
 

Investigators determined that the 22-ton rough terrain crane uses two lead acid batteries in series.  One battery is maintenance-free while the battery that exploded is the type that requires periodic maintenance.  Investigators speculated that the incident occurred when water in one of the battery's cells underwent electrolysis.  Investigators determined that when the water in a cell drops below the top of the cell's conductor, electrolysis can take place and produce hydrogen.  They also determined that electrolysis occurs when the charging voltage exceeds 2.4 volts per cell. Investigators determined that the battery did not have identification labels or adequate maintenance records, making it difficult to trace the battery's history.  Investigators belive that the potential ignition source was a spark from a poor battery terminal connection.  Investigators are waiting for the battery manufacturer's test report and will provide those results when they become available. 

As part of the on-site lessons learned program, facility management developed the following key points for personnel who work with and maintain lead acid batteries.
 

• If a battery is housed in a protective box personnel should ensure that the box and lid are intact and well vented before use.
• Personnel should follow prescribed safety procedures any time a battery is charged or jump-started.
• Personnel should avoid introducing ignition sources in the vicinity of batteries that are operating or being charged.
• Personnel should check terminals for corrosion or loose connections.
• While the operation, charging and discharging of lead-acid batteries does not normally produce explosive gases, overcharging a battery transforms it into an electrolysis machine that uses electric current to convert water into hydrogen and oxygen.  On maintenance-type batteries these gases are released through baffles in the cell caps.  The caps are designed to dilute and vent the gases to the surrounding atmosphere while preventing an external ignition source from backfiring into the battery cell.  On maintenance-free batteries these gases are gradually recombined into water.
• A charging voltage of about 2.4 volts or greater across any single cell is enough to produce explosive gases.  When the electrolyte bubbles, that is an indication that water is being converted into explosive hydrogen and oxygen.  It is important that personnel set the voltage of a battery charging system within the prescribed specifications.
• The electrolyte in lead acid batteries is diluted sulfuric acid.  Sulfuric acid is not consumed in normal battery operation, however in a maintenance-type battery water can evaporate or be electrolyzed.  If the electrolyte level falls low enough to expose the battery's lead plates they can become permanently sulfated and shorten the battery’s life.  Low electrolyte levels can also expose potential electrical faults within a battery cell and generate a spark that could ignite explosive gases inside the cell.
• Personnel should check electrolyte levels when servicing a maintenance-type battery and replace lost water.
• To avoid confusion, personnel should not place maintenance-type and maintenance-free batteries in the same battery compartment or use them on the same piece of equipment.

EH engineers identified the following similar event involving lead acid batteries. 
 

• Operating Experience Summary 99-12 reported that on March 8, 1999, at the Idaho National Engineering Environmental Laboratory Central Facilities Area, a utility operator was starting a diesel-driven fire water pump for a weekly test run when one of the associated batteries exploded.  He was approximately 20 feet away when the battery exploded and spilled approximately 1 quart of acid on the concrete floor.  The operator was not injured, so he secured the evolution and notified the appropriate supervisor of the explosion.  A protective plastic covering over the battery bank was damaged when the battery exploded.  No one had performed any inspection or surveillance of the facility firewater batteries.

(ORPS Report ID--LITC-CFA-1999-0003)
 

DOE-HDBK-1084-95, Primer on Lead-Acid Storage Batteries, provides information on the operation, construction, and maintenance of lead-acid batteries.  The handbook also provides information on the hazards associated with storage batteries and recommended precautions.  Information on battery chargers and charging operations is provided in the maintenance section.

KEYWORDS: battery explosion, battery charging, electrolysis

FUNCTIONAL AREAS: Industrial Safety, Electrical, Maintenance
 
 

Investigators determined that the fire ignited at points where the propane supply line and pressure gauge connect to the propane bottle and that the facility had six other propane bottles exhibiting similar leaks.  They determined that the bottle vendor performs quality assurance inspections on all bottles before they are shipped and that facility management did not perform a receipt inspection.  Investigators determined that facility management now requires a visual inspection of all gas bottles before they are stored or used.

EH engineers identified the following similar events involving leaking propane tanks.
 

• Operating Experience Summary 99-12 reported that on March 15, 1999, at the Oak Ridge East Tennessee Technology Park, Property and Materials Management personnel reported to facility supervision that a 150-lb propane cylinder was leaking in a covered but open storage shed.  Site protective forces blocked the streets around the storage shed, all personnel in the area were evacuated, and the site fire department responded to the scene.  A hazardous materials response team stopped the leak, using leak-patching equipment to seal the cylinder valve and valve cap.  After the leak was stopped, the cylinder was moved to a safe location.

(ORPS Report ORO--BJC-K25GENLAN-1999-0005) 

The requirements of 29 CFR 1910.101, "Compressed Gases," state that the in-plant handling, storage, and use of compressed gases in cylinders shall comply with Compressed Gas Association Pamphlet CGA P-1, Safe Handling of Compressed Gases. Pamphlet CGA P-1 costs $78.00 for nonmembers of the Compressed Gas Association.  (703) 412-0900, extension 799, between 0900 and 1630 EST.

KEYWORDS: propane bottle, compressed gas, fire watch, torch cutting, leak

FUNCTIONAL AREAS: Work Planning, Industrial Safety, Material Handling/Storage
 
 

On December 1, 1999, Depleted Uranium Operations (DUO) workers in Building 9201-5 were changing out the crucible in the skull caster furnace.  The workers were using a new procedure for the activity.  When workers removed a flexible argon purge hose from the crucible, several gallons of NaK sprayed out through an open isolation valve into the furnace.  Over the next several days, the workers monitored conditions in Building 9201-5 and intermittently purged the furnace with argon in an attempt to minimize further oxidation.  Facility management developed a recovery plan outlining the process for cleaning up the NaK spill.  On Friday, December 3, the workers observed unusual and unexpected conditions in the furnace, including a yellow color and abnormal configuration of the material.  Mineral oil was sprayed on the deposits to minimize oxidation.

On December 8, the explosion occurred while the workers were attempting to clean up the NaK using a vacuum probe and metal rod, having sprayed additional mineral oil.  The direct cause of the explosion was the impact of a metal tool on a shock-sensitive mixture of potassium superoxide (KO2 ) and mineral oil.  The December 1 NaK spill resulted from numerous deficiencies in the new procedure for crucible changeout.  During this work activity, the workers made pen and ink changes without stopping to obtain proper review and approval of the changes.  A key step requiring opening the dump valve to drain the crucible NaK piping had been inadvertently deleted from the procedure, resulting in a failure to open the valve to trap the remaining NaK under argon pressure.  When workers observed an unexpected NaK level in the sump, they did not stop to analyze the system configuration or seek assistance before repeating parts of the procedure.  A worker climbed into the furnace to disconnect the argon purge hose.  When the hose was disconnected, the trapped NaK sprayed out under pressure into the furnace through an open isolation valve that was also incorrectly aligned because of procedural deficiencies.

• Strengthening the implementation of ISM core functions and existing LMES processes to assure that all potentially hazardous work and activities are subjected to effective, formal, and documented hazard analysis.
• Strengthening the identification and implementation of engineering, administrative, and worker protection controls for potentially hazardous work and activities.
• Improving the identification, availability, and use of appropriate personal protective equipment to protect workers against work-related hazards.

The full report can be found at http://www.eh.doe.gov/oversight/acc_inv/y-12_report/.

 
KEYWORDS: injury, chemical, procedures, sodium, potassium

FUNCTIONAL AREAS: Explosion, Personnel Injury, Work Activity