A review of a recent explosion investigation with an unusual cause.
Explosive Weather – An Explosion Investigation Case Study, shows how using the Scientific Method and the steps laid out in NFPA helps Meier Fire’s Exoert, Richard Meier to find the unusal case
A case study of a commercial explosion investigation by Richard J. Meier, Meier Fire Investigation, LLC
Summary of the Explosion Incident
On Sunday, September 10, 2017, at approximately 11:00 pm, an explosion occurred on the first floor of a group home for the mentally challenged in Florida, run by a non-profit organization. That evening, Hurricane Irma, a Category 4 storm, was passing over the area. Sustained winds topped 100 mph, and gusts measuring even higher. The storm tore roofs from homes, uprooted trees, and snapped utility poles and power lines across the state.
Prior to the explosion, the surviving residents and neighbors reported several events happening at the house. They related seeing and hearing multiple flashes and “bangs” as the power line parted and grounded about 9 pm. At the same time, the home lost power and the fire sprinkler in the first floor laundry room activated. Residents were unsure if they smelled gas in the home. Due to the weather, the residents were effectively trapped. Approximately 2 hours later, the explosion occurred.
Explosion Investigation Details
An examination of the scene found varying degrees of damage throughout the home. This included pushed walls and cracked drywall. Fire sprinklers had activated in several locations on the first floor, although the fire damage was limited to a small area of the laundry room. Heat damage was evident in various locations on the first floor. Absent from the scene were any broken windows. All signs pointed towards the occurrence of a low order explosion, and a fuel mixture at the low end of the flammability range. The only fire following the explosion was in the laundry room behind the clothes dryer.
Signs pointed to a diffuse fuel explosion. The fire damage behind the dryer in the laundry room indicated the fuel gas used in the home. The minimal explosion damage and lack of significant fire damage indicated a relatively low-pressure event, and a low order explosion. Lack of damage to a rear door combined with damaged screen on the rear porch indicated door was open during the explosion.
CSST Gas Line Failure
Analysis of the evidence revealed several pin-sized holes in the CSST (corrugated stainless-steel tubing) flex line connecting the dryer to the houses fuel gas system. This type of damage is common during lightning strikes, but lightning is extremely rare during hurricanes. During the exam, we found charring around the power receptacle for the dryer
On the outside of the home, damage was noted to a fire sprinkler riser (a vertical steel pipe in the yard), and the fire and security alarm systems.
It was confirmed that a high voltage power line had fallen from poles near the house during the storm. The power lines ran next to the home, transitioning from overhead to underground lines.
Nearby in the yard was a vertical riser from a sprinkler supply line connected to the home. Ostensibly this was for connection to another home to be built at a future date. Examination of the riser revealed multiple arc strikes had recently occurred.
Case Study: Explosion Investigation Images
Figure 5. A portion of the flexible gas line collected at the scene. Numerous holes (yellow arrow) and splatter (red arrows) are present in the line. (MFI photo) Figure 6. Electrical receptacle for the clothes dryer in the laundry room. Charring around the grounding pin receiver indicates abnormal electrical activity. (MFI photo) Figure 7. Standpipe for the fire suppression system. Discoloration of stucco is indicative of heating taking place on pipe and electrical boxes. (MFI photo) Figure 8. Junction box for flow sensor in the standpipe. Cover is bulged and melted, and gasket blown out. (MFI photo) Figure 9. Downed wire on a 3-phase high voltage transmission line. (Supplied photo) Figure 10. Pipe connection on fire sprinkler supply run next to the home. (MFI photo) Figure 11. Pipe show evidence of multiple arc strikes. (MFI photo) Figure 12. Home (1), fire sprinkler riser (2), power pole (3), and sprinkler water pipe (4). (Nancy Smith photo)
Case Study: Explosion Investigation Conclusions
After the examination and analysis, it became clear what had happened to cause the explosion.
- High winds blew down the power line, which came into contact with the sprinkler water supply line.
- One or more power surges knocked out power to the building, burned holes in the CSST line supplying the clothes dryer, and also caused the laundry room sprinkler to activate by bursting the frangible bulb.
- The sprinkler water partially scrubbed the odorant from the fuel gas, preventing the occupants from properly identifying the source of a gas odor.
- A candle or lighter provided the ignition source for the fuel gas.
While this incident occurred in a commercial/residential setting, it could just as easily have occurred in a commercial or industrial one. We can all be the victims of extreme weather, and the consequences of that weather as well.
