ARCO SPELLS OUT CAUSE OF CHANNELVIEW BLAST

ARCO Chemical Co. officials are 95% sure excessive oxygen in the vapor space of a waste water storage tank led to an explosion and fire last year at ARCO's Channelview, Tex., petrochemical plant.

Explosive conditions developed when a key oxygen analyzer failed in a way that led plant operators to believe they were operating safely, ARCO said.

The blast, just before midnight July 5, 1990, killed 17 workers and flattened an area the size of a city block, shutting down 15% of U.S. styrene monomer capacity (OGJ, July 16, 1990, p. 28).

ARCO earlier this month agreed to pay $3,481,300 in penalties proposed by the U.S. Occupational Safety and Health Administration for alleged willful and serious violations of the Occupational Safety and Health Act. The amount was the largest monetary settlement with OSHA on record for safety violations.

OSHA last year proposed fines totaling $5,666,200 against Phillips 66 Co. as a result of explosions and a fire that killed 23 persons Oct. 23, 1989, at Pasadena, Tex. Phillips has not settled with OSHA. Based on its investigation of the accident, it is contesting all citations issued by the agency (OGJ, May 28, 1990, p. 36).

SAFETY MEASURES

As part of its settlement, ARCO agreed to undertake a major revamp of safety training and process safety management programs at all its U.S. plants (OGJ, Jan. 7, Newsletter).

Since the accident, ARCO has spent $36 million to rebuild and upgrade equipment in Channelview's waste water treatment area, including $20 million to add redundancy in system safeguards.

"Where we had three tanks before in that process waste stream operation, we now have eight," he said. "Where we had one oxygen analyzer, we now have 16.

"Where we had one source of nitrogen, we now have a backup nitrogen supply that sweeps tank vapor to flare on a continuous basis."

ARCO said accepting OSHA's proposal and agreeing to pay the fine did not affirm the accuracy of OSHA allegations, characterizations of its alleged conduct, or conclusions set forth in OSHA's citations.

Rather than dispute areas in which ARCO's findings differ from OSHA'S, "we decided it served everyone better if we focused on improving safety of our operations," said Jack Johnson, president of ARCO Chemical Americas.

ACCIDENT SCENARIO

Channelview plant's 900,000 gal storage tank, which was demolished by the explosion, received and temporarily stored waste water from the plant's propylene oxide-styrene monomer (POSM) unit prior to injecting treated liquids in a deep disposal well on site.

Waste water held in the atmospheric pressure tank contained light hydrocarbon liquids, including hydrocarbon peroxides, that released oxygen and flammable hydrocarbon gases into the tank's vapor space.

The atmosphere in the vapor space was sampled by an oxygen analyzer, which provided operators in the control room a continuous readout of oxygen concentrations. An inert nitrogen sweep system purged excess oxygen from the tank atmosphere, along with hydrocarbon vapors.

ARCO used a compressor to move the vapor stream from the tank to a pressurized recovery tower in the PO SM unit, which scrubbed hydrocarbon vapors.

The waste water treatment system had operated safely and reliably for several years, ARCO said.

But OSHA alleged that from about June 15, 1990, through the time of the explosion the oxygen analyzer malfunctioned, reducing the nitrogen purge to an ineffective level and allowing excessive oxygen to accumulate in the tank vapor space.

The analyzer showed the low rate of nitrogen sweep was adequate for the oxygen concentration present.

"In reality, however, oxygen was accumulating faster than the reduced nitrogen sweep could purge it from the tank," ARCO said.

In late June, the compressor that moved the purged vapor stream to the PO-SM unit failed, and ARCO removed it for repair.

In the backup mode, the oxygen analyzer continued sampling gases and sweeping the tank vapor space with nitrogen. But the vapor mixture-thought by plant operators to be inert-was vented to the atmosphere, a procedure that had been followed safely before ARCO began capturing and scrubbing tank vapors as part of an environmental upgrade.

On July 4, about 34 hr before the explosion, workers shut down the nitrogen sweep to modify piping and instrumentation before returning the compressor to service. Because the faulty analyzer continued to show safe oxygen levels, plant operators allowed the nitrogen sweep to remain off until workers began reinstalling the compressor just a few minutes before the explosion, ARCO said.

As a result, ARCO concluded, energy provided by normal operations such as restarting the compressor would have been enough to ignite the vapor.

SETTLEMENT DETAILS

Although employees of several contract firms were working at Channelview at the time of the explosion, OSHA held ARCO solely responsible for the accident because ARCO maintained total control of the site and dictated working conditions.

OSHA fined ARCO $10,000 each for 347 alleged willful violations of endangering employees on duty at the time of the accident. The agency added a total penalty of $11,300 for 16 alleged serious violations,

OSHA defines willful violations as acts committed with intentional disregard or indifference to requirements of the OSHA act. OSHA defines serious violations as actions resulting in substantial probability of death or serious injury when the employer knew or should have known of the hazard.

ARCO had until Jan. 10 to pay the fines.

In addition to paying fines assessed by OSHA, ARCO agreed to:

Within 30 days of the Jan. 3 agreement assemble a process hazard analysis staff for each of its four U.S. plants.
Within 270 days of the agreement complete process hazard analyses at each plant and report results to appropriate regional OSHA offices.
Within 30 days of completing process hazard analyses provide appropriate OSHA area offices with written management responses.
As soon as practical but in no event later than 1 year from completion of step three implement actions recommended by process hazard analyses and/or written responses.