An explosion is reviewed for its mechanism, wherever it happened
We review explosions and flash fires in settings including a process unit at a refinery or chemical plant, a wellsite or tank battery, a construction site, a warehouse or grain facility, a pipeline, a fuel terminal, a vehicle, or a home or small business supplied with natural gas or propane. The investigation follows the mechanism of injury as well as the place. The companies, the operation, and the coverage questions are reviewed with each setting; the event’s mechanism also needs its own reconstruction.
The vocabulary matters because the words are used loosely. An explosion is a rapid release of energy that produces a pressure wave, whether from a burning gas or vapor cloud that was confined, from a dust cloud in an enclosure, or from a vessel, tank, or line that failed under pressure. A flash fire is the rapid burning of a flammable cloud without a significant pressure wave. A vapor cloud is a release of flammable gas or vapor that drifts until it disperses or finds an ignition source. A blast injury is the injury the pressure wave causes; burns from the fire that follows are reviewed for their medical course as burn injuries.
Combustion: fuel, ignition, and confinement
A blast can result from combustion, overpressure, or catastrophic equipment failure. The review begins by identifying the energy source, what initiated the event, and how pressure developed or was confined. Where fuel ignited, the investigation also identifies the release and ignition source. The answers are often written down before the event in permits, operating records, inspection files, and the records required by workplace rules.
Flammable liquids are classified by flashpoint and boiling point, and the rules for storing, transferring, and using them depend on the category. Propane and other liquefied petroleum gases must be odorized so that a leak can be smelled well below the concentration at which the gas can burn, which is why the absence of odor after a propane event is itself a question. Natural gas distributed to homes and businesses is also odorized.
Combustible dusts from grain, wood, metals, plastics, and other materials can explode when suspended in an enclosure, and OSHA runs a national emphasis program directed at combustible-dust hazards, with a specific standard for grain-handling facilities.
Electrical equipment in areas where flammable vapors, gases, or dusts may be present must be suited to the classification of that location, which is recorded on the facility’s area-classification drawings. Facilities covered by the process safety management rule keep hazard analyses, operating procedures, and management-of-change records that describe how the process was meant to keep fuel and ignition apart, a rule explained with refinery accidents.
Hot work, static, electrical equipment, and other ignition sources
Investigators check ignition sources by category: hot work such as welding, cutting, and grinding; static discharge during transfers of liquids or powders; electrical equipment not rated for the location or not maintained; hot surfaces such as exhaust systems, heaters, and bearings; vehicles and engines; open flames and smoking; and lightning. Each category leaves a record, and hot work leaves the most. Where flammable materials may be present, hot work is controlled by a permit that records the location, the tests made for flammable atmospheres, the isolation of nearby equipment, and the fire watch assigned to stand by during and after the work. Process facilities must issue such permits for hot work on or near a covered process, and the welding and cutting rules require a fire watch wherever more than a minor fire might develop. A permit is a contemporaneous statement of what the companies believed the atmosphere to be and what they did to confirm it.
Reconstructing the minutes before ignition
The minutes before an explosion are reconstructed from records that were being made for other purposes.
- Fixed and portable gas-detection logs, alarm set points, and calibration records show what the detectors read and whether they were working.
- Permits to work, hot work permits, confined-space entry permits, and isolation, lockout, purge, and line-breaking records show what work was authorized and what checks were made.
- Control-system trends and alarm journals show pressures, temperatures, levels, and flows and each operator action, at short intervals, for a process unit.
- Camera footage, gate and badge records, radio recordings, and dispatch audio place people and vehicles in time.
- Witness positions and accounts, the pattern of damage, and the seat of the blast identified by fire investigators locate the origin.
- The physical evidence itself, including failed vessels, valves, fittings, regulators, hoses, and detectors, carries the marks of what happened to it.
Much of this is lost quickly. Detection and control-system data are overwritten on a schedule, camera systems often keep footage only briefly, and cleanup and demolition remove the physical evidence within a short time of the event. The firm identifies every company with a role in the area, asks each by name to preserve what it holds, and asks that no failed component be repaired, scrapped, or subjected to destructive testing until every party has had the opportunity to document it.
Fire marshals, OSHA, the Chemical Safety Board, and pipeline regulators
Several agencies may investigate the same explosion, each for its own purpose. In the Houston area, the Harris County Fire Marshal’s Office is responsible for fire, arson, and explosion investigations in unincorporated Harris County and coordinates with the district attorney; the Houston Fire Marshal’s Office investigates origin and cause within the city; and the State Fire Marshal’s Office investigates fires involving death, injury, or significant property damage when a local authority requests it, with the power to enter the premises and to take sworn statements. Those investigations produce origin-and-cause reports, photographs, evidence logs, and statements, some of which are withheld while a criminal investigation is pending. Their question is whether a fire was set intentionally, carelessly, or accidentally, not which company bears civil responsibility.
The Occupational Safety and Health Administration may inspect a workplace after a reported fatality or hospitalization; the inspection file is a record source, and a citation is evidence that counsel weighs rather than a decision, as with any workplace injury. The U.S. Chemical Safety and Hazard Investigation Board is an independent federal agency, established by statute, that investigates the facts, conditions, circumstances, and cause or probable cause of selected accidental chemical releases that result in a fatality, a serious injury, or substantial property damage. It is not a regulator; it issues no fines or citations, it interviews witnesses, collects documents, and sends samples and equipment to independent laboratories, and it publishes its reports and safety recommendations. Federal law bars the Board’s conclusions, findings, and recommendations from being admitted as evidence or used in any action for damages arising out of the incident it investigated, so its report is a source of facts and records rather than a decision.
Pipelines and propane have their own regulators. The Railroad Commission of Texas regulates the storage, distribution, and use of liquefied petroleum gas in Texas and the safety of intrastate gas and hazardous-liquid pipelines, and it is certified to enforce the federal pipeline safety rules for those lines; interstate pipelines are overseen by the federal Pipeline and Hazardous Materials Safety Administration, whose southwest regional office is in Houston. Pipeline operators must notify the National Response Center within an hour of confirming a reportable release and must file written accident reports for a fire, an explosion, or a release above a threshold volume. Those filings, together with leak surveys, odorization records, and damage-prevention and locate records, are the pipeline record. Fire and explosion investigators in the United States also commonly work from a professional guide to fire and explosion investigation published by the National Fire Protection Association; it is a recognized methodology, not a law.
Evacuations, shelter-in-place orders, and what they do not prove
A workplace covered by an emergency action plan must have a written plan, kept at the workplace, with procedures for evacuation, for accounting for every employee afterward, and for an alarm system. When an explosion or a release threatens people beyond the fence, Harris County’s emergency management office and the affected cities issue shelter-in-place notices instructing residents to go indoors and close doors and windows until the hazard is controlled. Those notices, the facility’s evacuation and head-count records, the fire department’s dispatch and incident reports, and the air-monitoring records taken during the response are records of what was known, when, and to whom it was communicated. They establish the timeline and identify who was affected. They do not by themselves establish who was responsible.
Refineries, wellsites, construction sites, pipelines, and homes
- An explosion in a process unit is reviewed here for the mechanism and as a refinery accident for the facility, its contractors, its permits, and its process-safety records.
- An ignition on a wellsite or at a tank battery is reviewed here for its mechanism, while the oilfield accident review catalogues the wellsite’s ignition hazards, the companies on location, and the Railroad Commission’s records.
- A gas line strike, a propane cylinder, or hot work on a construction site is reviewed here for the mechanism and as a construction accident for site control and the trades.
- A pipeline rupture is reviewed here for its mechanism, with the pipeline regulators’ records described above; which companies stand behind it is a third-party workplace claim question when the injured person was at work.
- A residential or small-business gas or propane explosion is reviewed here for its combustion mechanism, with the utility’s, dealer’s, and property owner’s records; whether an appliance, regulator, or connector failed is a defective product question.
- A vehicle fire after a collision is reviewed as a car accident or a truck accident for the collision and as a defective product question for the fuel system; the fire’s mechanism also needs reconstruction.
Burn injuries, exposures, and deaths after an explosion
People hurt in an explosion may be burned, may have been exposed to what was released before or after the fire, and may have died. Burn treatment and recovery are reviewed separately. What was released, in what concentration, and for how long is a chemical exposure question when the substance was inhaled or contacted without igniting, and a single event can raise different questions for different people. A death brings in the family and estate questions of a wrongful death claim. Which of the companies involved stands inside the injured worker’s workers’ compensation relationship and which is a third party is decided for each company.
Talking with the firm after an explosion
An explosion review starts with the place and time of the event, the injured person’s employer and the other companies in the area, what was being done in the minutes before, whether a permit was in force, who responded, and the medical care so far, followed by any photographs, notices, and paperwork the injured person or the family has kept. A consultation begins with the mechanism and the records, and the firm asks each company to preserve the physical evidence and the data before any of it is cleaned up, repaired, or overwritten.