Posted on: May 24, 2010 Posted by: Diane Swarts Comments: 0

A gas explosion after pipeline purging by gas jet at Kleen Energy gas power plant in the USA on 7 February 2010 killed seven and injured 12 workers.

The accidental blast occurred during planned work to clean debris from natural gas pipes at the plant. To remove the debris, workers used natural gas at a high pressure of approximately 650 pounds per square inch.

High velocity of the natural gas flow was intended to remove any debris in the new piping. At pre-determined locations, this gas was vented to the atmosphere through open pipe ends less than 20 feet off the ground.

The vents were adjacent to the main power generation building and along the south wall, and the explosion confined in the ‘courtyard’ between two jutting wings of power plant, caused serious blast damage and fire damage.

Relevant safety regulations are mostly voluntary, and in the case of the Kleen Energy plant, there does not appear to be any specific violation of relevant USA legislation, but gases must be vented in open areas, not near ignition sources or workers, reports the HSE committee of G4S Security Services in Jakarta, Indonesia after studying the incident.

It had been previously recommended that purges be conducted with as few workers on site as possible and with the gas piped far away from the structure, but this was a recommendation, and not binding.

In light of this accident, the Chemical Safety Review Board has urged a moratorium on purges using natural gas.

Natural gas is a potentially explosive substance. When gas is isolated in a pipeline, it can’t explode, because there is no oxygen to allow combustion.

Once released, the gas mixes with air, creating a potentially dangerous fuel-air explosive. Natural gas can ignite at concentrations as low as 4%. When it is vented, it is critical that the area be thoroughly ventilated to assure that the gas is completely dispersed.

Natural gas is primarily methane and therefore is lighter than air. Methane tends to disperse upward, but this property can also be problematic if there is a roof or overhang, which the gas may become trapped under.

Gas was not released in an open space, but on the premises, in the middle of equipment and structures and only slightly outside of the main building.

Reports indicate that the gas release pipe was located in an enclosed area behind one of the combined cycle plant’s heat recovery boilers, with the gas being blown out into a cavernous area between the two boilers.

This ‘courtyard’ is where the explosion occurred. It’s possible that the gas could have flowed back into the covered structure, given its close proximity. The dispersal would depend largely on wind, but would undoubtedly be impeded by the structures in the area.

Total amount of gas released in one of these purges is upwards of 400 000 cubic feet. The enclosed space where the venting took place was called “inherently unsafe” by the chemical safety review board.

Rate of dispersal of methane depends on a number of factors. Gas will disperse much faster in open spaces, and wind will help accelerate the dispersal.

Sheltered areas may contain gas for some time, and a drop in temperature from gas release will cause an increase in the density of gas. Cold natural gas may linger near the ground until it warms up enough to be lighter than air.

Gas discharge in a sheltered area with overhangs and near workers and equipment, is a disaster waiting to happen. Tere was welding equipment in the area that had not been checked.

There were also a number of torch type heaters in the area, which burned propane in an open flame with minimal protection.

Welders had been working on the site around this time. There was an open flamed heater. Workers were never ordered to avoid the area or stop doing work that may spark.

Open flamed heaters were not shut down for the natural gas purge. The purge procedure may have constituted gross negligence and lack of due concern for safety.

Workers at natural gas companies are told to get all non-essential persons away from an area at the very smell of gas. Methane does not have a smell, chemicals like mercaptans are added to give it a smell.

Dangers of natural gas are well known. In one notorious incident, nearly 300 people were killed when a Texas school exploded in 1937.

Hazardous work requires a culture of safety and oversight, as in the oil gas, and nuclear industry.

An analysis of primary contributing causal factors, or root cause analysis, by the USA Chemical Safety and Hazard Investigation Board, known as Chemical Safety Board, CSB, concluded that gases must be vented in open areas, not near ignition sources or workers.

PHOTO: Release of compressed purging gas in a relatively confined area. The chilled gas sank down among the power station structures, forming pools of explosive mixtures with air. Nearby heaters or welding work triggered the blast. The photo was taken minutes before the explosion.

* Source; Lesson Learned, by HSE committee of G4S Security Services, Jakarta, Indonesia, Indra.wardhana@id.g4s.com or www.g4s.com

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