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H2Incidents: Hydrogen Incident Reporting and Lessons Learned

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Definitions

Incident
An incident is an event that results in:
  • a lost-time accident and/or injury to personnel
  • damage to project equipment, facilities or property
  • impact to the public or environment
  • an emergency response or should have resulted in an emergency response.
Near-Miss
A near-miss is an event that, under slightly different circumstances, could have become an incident. Examples include:
  • any unintentional hydrogen release that ignites, or is sufficient to sustain a flame if ignited, and does not fit the definition for an incident
  • any hydrogen release which accumulates above 25% of the lower flammability limits within an enclosed space and does not fit the definition of an incident
Non-Event
A non-event is a situation, occurrence, or other outcome relevant to safety that does not involve a particular incident or near miss. For example, a non-event might consist of a failed safety inspection.
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Incident Report

Hydrogen Explosion in a Concrete Block Production Plant

Incident Date: 2007

 

Severity:
Incident

Was Hydrogen released?
Yes

Was there Ignition?
Yes

Ignition Source: spark from a faulty lamp

Description

A trained operator was blending water, sand, anhydrite, lime, cement, pulverized fly ash, and powdered aluminum in a mixing chamber to produce material for making concrete building blocks. In the blending process, sand and water are mixed to form a slurry, and then the powders are dispensed automatically into the mix by a computer-controlled system. Finally, a slurry of glycol-coated aluminum powder is added in the last few seconds before the mix is discharged into a car, and then molds are filled from the car. Adding aluminum to the mixture results in a small amount of hydrogen gas evolution, which disperses from the car into the surrounding ventilated area and out through roof vents. In addition to being an ingredient of the mix, water also helps to keep the mixture cool.

During a break in production, the operator took the opportunity to wash out the mixer in accordance with his work instructions. He did this by manually emptying out the water hopper, but he neglected to refill the hopper. When he switched the controls back to automatic, the program software did not realize that the hopper was empty since the digital readout still said "full".

During the subsequent mixing batch, the operator noticed an "excessive mix time" alarm on the mixer panel. This alarm stops the process and dumps the mixer contents. The operator noticed an inconsistency in the mixed material discharge, which was more like a sludge than a fluid concrete. He realized that there must have been a blockage and followed the written procedure by taking manual control and introducing as much water as possible to thin and cool the mix by opening the water hopper valves. During this process, a second alarm went off reading "mix temperature invalid", indicating that the mix temperature was not within the acceptable range of 0-99C.

The operator went up to the mixer platform to investigate the reasons for the alarms and the mix inconsistency. He lifted the mixer inspection hatch and used an inspection lamp (later revealed to be faulty) to illuminate the interior of the mixer. The ensuing explosion resulted in temporary injuries to the operator, including loss of sight, burns, and cuts. He was wearing the correct PPE, including safety glasses and a hard hat, which were both blown off by the blast.

Setting

Equipment

Process Equipment

Damage and Injuries

Probable Cause(s)

Contributing Factors

No Characteristics Defined.

The incident was discovered During Operations.

Lessons Learned/Suggestions for Avoidance/Mitigation Steps Taken

The company investigation revealed that the incident arose because insufficient water was added to the batch. This resulted in a rapid increase in temperature and evolution of hydrogen gas following the addition of aluminum powder in the last seconds of the mix. Despite the presence of a functioning level-control valve on the mixer, the hydrogen gas was ignited when the operator opened the hatch. The most likely source of ignition was the faulty lamp. The operator was acting in accordance with his training and following the company's written safety procedures.

The company took a number of measures to prevent a reoccurrence of this incident, including:

provision of intrinsically safe lamps
introduction of daily checks of the vent valve
minor modification to LEV and increased venting throughout the mixing process
lab testing by the aluminum supplier to evaluate system safety with regard to hydrogen generation for all reaction conditions and quantities of aluminum added
reprogramming/development of the software to improve both the safety of the operation and operator understanding of warning alarms.

Date Added to H2Incidents: 3/30/2012