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Watson Grinding Fatal Explosion and Fire

Overview

On January 24, 2020, a propylene leak from the Watson Grinding and Manufacturing Co. HVOF thermal spray process accumulated inside the coating building and ignited. The explosion and fire fatally injured two employees and a nearby resident. Two additional employees were injured. Hundreds of nearby structures were damaged. The CSB final report identified a disconnected hose inside Booth 4 as the immediate leak source and cited deficiencies in process safety management and emergency preparedness.

Incident Snapshot

Field Value
Facility / Company Watson Grinding and Manufacturing Co.
Location Houston, TX
Incident Date 01/24/2020
Investigation Status The CSB's final report was release June 29, 2023.
Accident Type Explosion and Fire
Final Report Release Date 06/29/2023

What Happened

  • On January 23, 2020, the coating booth operators shut down the individual booths following a normal workday, and the Coating Supervisor closed and locked the coating building.
  • The Coating Supervisor did not close either of the two manual shutoff valves located at the propylene storage tank.
  • At some point overnight, the propylene hose in Booth 4 disconnected from its fitting, creating a propylene release from the propylene storage tank through piping into the booth.
  • Shortly before 4:30 a.m. on January 24, 2020, an accidental release of propylene accumulated and exploded inside the Watson Grinding coating building.
  • At about 3:55 a.m., Employee Two detected a chemical odor outside the Watson Gym.
  • At approximately 4:00 a.m., Employees One and Two walked to the coating building and smelled a strong propylene odor and heard a really loud hissing noise coming from inside the building.
  • At 4:04 a.m., Employee Two texted the Coating Supervisor that gas was leaking out of Booth 4.
  • At 4:07 a.m., Employee Two called the Plant Manager, notifying him of the propylene leak.
  • At 4:19 a.m., the Coating Supervisor texted all coating booth operators that Booth 4 had a potential leak and not to start up yet.
  • At approximately 4:24 a.m., Employee Four arrived at the facility.
  • As Employee Four backed his truck into a parking space, the flammable propylene vapor ignited and the coating building exploded.
  • The explosion fatally injured Employees Two and Three and injured Employees One and Four.
  • The explosion destroyed the coating building and caused heavy damage to the administration building and valve shop.
  • The CSB estimated that approximately 2,600 pounds of propylene were released.
  • Watson Grinding filed for bankruptcy on February 6, 2020, and the company is no longer in business.

Facility and Process Context

  • Watson Grinding and Manufacturing Co. operated specialty thermal spray coatings, particularly High Velocity Oxygen Fuel (HVOF) coating.
  • The coating building had eight coating booths; six of these booths used HVOF spray coating and two booths used plasma coating.
  • Booth 4 was one of the HVOF coating booths inside the coating building.
  • Propylene was used as the fuel for the HVOF coating process.
  • Propylene was stored in a 2000-gallon bulk tank and routed through propylene supply piping to the coating booths.
  • Each HVOF coating booth was designed to include fixed atmospheric monitoring equipment.
  • The safety system included daily manual leak checking of some propylene piping components inside each booth, automated controls to start and stop propylene flow during coating application, and remote shutoff buttons inside the coating building.
  • The coating booths inside the coating building were designated as Class I, Division 2 locations.

Consequences

  • Fatalities: Two employees and a nearby resident died.
  • Injuries: Two additional employees were injured.
  • Environmental release: The CSB estimated that approximately 2,600 pounds of propylene were released.
  • Facility damage: The explosion destroyed the coating building and caused heavy damage to the administration building and valve shop; hundreds of nearby structures, including homes and several businesses, were damaged.
  • Operational impact: Watson Grinding filed for bankruptcy on February 6, 2020, and the company is no longer in business.

Key Findings

Immediate Causes

  • A disconnected hose inside one of the facility’s coating booths caused the propylene leak.
  • A degraded and poorly crimped rubber welding hose disconnected from its fitting inside Booth 4.
  • The propylene vapor likely ignited when an employee entered the coating building and turned on the lights.

Contributing Factors

  • A lack of effective process safety management practices at the facility.
  • A lack of emergency preparedness at the facility.
  • The emergency response plan did not address responding to a propylene gas leak.
  • Watson Grinding did not train its employees to recognize or respond to a propylene gas release.
  • Neither supervisor reported directing Employee Two to evacuate himself and others from the facility immediately.

Organizational and Systemic Factors

  • The lack of a comprehensive process safety management program.
  • The absence of critical process safety information.
  • The absence of a hazard assessment of the propylene process.
  • The absence of a mechanical integrity program.
  • The absence of a management of change review.
  • The absence of written operating procedures.
  • Watson Grinding did not maintain engineering drawings and additional documentation on the automated gas detection alarm, exhaust fan startup, and gas shutoff system.
  • Watson Grinding did not maintain this system in working order.
  • Watson Grinding did not train its employees on effectively using or maintaining the system.
  • Watson Grinding did not follow the designer’s recommendation to conduct a hazard assessment of the coating booths.
  • Watson Grinding did not maintain critical process safety information for the automated gas detection alarm, exhaust fan startup, and gas shutoff system.
  • Watson Grinding did not effectively respond to reports in 2013, 2016, 2019, and two weeks before the incident that the gas detection alarm, exhaust fan startup, and gas shutoff system were not connected to the PLC.
  • Watson Grinding had no testing program in place to ensure the functional integrity of the automated gas detection alarm, exhaust fan startup, and gas shutoff system.
  • Watson Grinding did not have a procedure for crimping, nor were its employees formally trained on how to properly crimp fittings onto the rubber welding hose.
  • Watson Grinding lacked a written coating system shutdown procedure.
  • Watson Grinding did not implement consistent work practices.
  • Watson Grinding did not formally train its workers to recognize or respond to a propylene gas release.

Failed Safeguards or Barrier Breakdowns

  • The automated gas detection alarm, exhaust fan startup, and gas shutoff system was not functional at the time of the propylene leak.
  • The gas detection system was no longer capable of automatically triggering alarms, starting up the exhaust fan, or shutting off the propylene supply if a dangerous concentration of propylene accumulated in a coating booth.
  • The alarms did not activate.
  • The exhaust fan did not start up.
  • The remote shutoff valve at the propylene storage tank did not close.
  • Daily manual leak checking of some propylene piping components inside each booth.
  • Automated controls to start and stop propylene flow during the coating application.
  • Multiple buttons inside the coating building to remotely shut off the supply of propylene and other gases.
  • Fixed atmospheric monitoring equipment with automatic alarm and isolation functions.

Recommendations

  1. 2020-03-I-TX-R1 | Recipient: Compressed Gas Association (CGA) | Status: Closed – Acceptable Action | Summary: Urge member companies that handle hazardous chemicals to share information with their customers about the safety issues described in this report and why their customers should develop and implement effective process safety management systems, including informing customers about CGA P-86, Guidelines for Process Safety Management, the Center for Chemical Process Safety’s Guidelines for Risk Based Process Safety, or an equivalent approach.
  2. 2020-03-I-TX-R2 | Recipient: Matheson Tri-Gas Inc. | Status: Closed – Acceptable Action | Summary: Provide customers with information about the safety issues described in this report and why they should develop and implement effective process safety management systems, including informing customers about CGA P-86, Guideline for Process Safety Management, the Center for Chemical Process Safety’s Guidelines for Risk Based Process Safety, or an equivalent approach.

Key Engineering Lessons

  • A disconnected or poorly crimped hose in a propylene HVOF system can create a large flammable gas release if mechanical integrity is not maintained.
  • Automatic gas detection, exhaust fan startup, and gas shutoff functions must be maintained in working order and verified by testing so they can respond to a leak.
  • Remote shutoff and manual isolation valves are only effective if operating procedures require them to be closed when production ends and personnel are trained to use them.
  • Process safety information, hazard assessments, and management of change are necessary to identify and control hazards in coating booth gas systems.
  • Emergency response planning must address the specific hazards of propylene releases and include employee training on recognition, evacuation, and notification.

Source Notes

  • Priority 1 final report information was not provided in the extract set; the consolidated record relies primarily on the final report supporting document and recommendation status summaries.
  • Where documents differed, higher-priority recommendation status summaries were used to set recommendation status to Closed – Acceptable Action.
  • The incident involved Watson Grinding and Manufacturing Co. in Houston, Texas, on January 24, 2020.
  • The final report supporting document states that a nearby resident died a week later; the recommendation summary states a member of the public was fatally injured. Both are preserved in the consolidated consequences as a nearby resident died.

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