Aerosol Explosion - Wasp & Hornet Spray
A gentleman had purchased two large aerosols of wasp & hornet spray and had placed them on an air conditioning unit next to his garage.
Cans on AC Unit
|A day or two later, he noticed that they were still sitting on the AC unit and decided to move them to a nearby brick wall that was about 4 feet high. After he set the second can on the top of the concrete wall and just removed his hand, the bottom of the can exploded off and the body became a rocket and hit him in the face causing serious facial and eye injuries. Witnesses described the can as having both the top and the bottom gone (or possibly open).|
A complicating factor in the investigation was that neither of the containers were available for inspection. It was said that the paramedics may have thrown away the non-exploded container and that the other one somehow had gone missing from the hospital before the injured man was discharged. Not having the direct physical evidence always makes an investigation more demanding.
The investigation focused on determining the pressure vs. temperature behavior of exemplar wasp & hornet sprays and the temperature increase caused by the AC unit. On a day when the weather was similar to the day of the incident, two containers of wasp & hornet spray were positioned on the AC unit and heavily instrumented with thermocouples. It was thus determined that the maximum temperature to which the wasp & hornet spray could have been heated was 110° F. This was corroborated by the fact that injured man moved the cans without any gloves. Hence, the cans were most likely not above 120° F.
Based on the experimentally measured pressure versus temperature behavior of the wasp & hornet spray, it was determined that the pressure at 110° F (on the day of the incident) could not have exceeded 125-135 psig.
The wasp & hornet spray was packaged in a DOT 2Q, three-piece steel container. The minimum burst requirement for a DOT 2Q container (per Department of Transportation) is 270 psig. Since it was experimentally determined that the maximum internal pressure of the wasp & hornet spray was 135 psig at the time it exploded, it was concluded that the container must have been defective in that it did not meet the DOT minimum burst requirements. Since the actual container that exploded was not available, the exact nature of the defect could not be determined. At the same time, the scientific evidence and sworn testimony left no alternative but to conclude that it had to have been defective.
Another factor that played an important role was a publication by aerosol industry experts whose data forces the conclusion that whenever the bottom explodes off of an aerosol container, the bottom must have been defective. This is because in non-defective aerosols the tops explode off before the bottoms.
One aspect of the case that needed to be explained was that witnesses who saw the exploded container testified that both the bottom and top of the container were missing (or open). This was accomplished by a heat-to-burst test aimed into a wood wall covered with a moving blanket for some minor cushioning. First, an intentional defect was put into the bottom of the container to make the bottom explode off first. This turned the body into a rocket that slammed top-first into the wood wall. The plastic cap was left on the container as it was on the day of the incident. The result was a container that was missing the bottom completely (exploded off) plus the top was forced open by the impact.
During the course of the investigation many experimental tests were performed on exemplar wasp & hornet aerosols, including metallography, several heat-to-burst tests, water bath simulation tests (another DOT requirement) and pressure versus temperature tests. The case settled before trial.
Dr. Michael Fox of Chemaxx has successfully completed courses in Aerosol Technology given by The Center for Professional Advancement as well as the British Aerosol Manufacturers Association. He is also formally trained in Department of Transportation Regulations for the transportation of hazardous materials (the DOT regulates aerosol containers and the product that can go in them).
Dr. Fox is also a Certified Fire & Explosion Investigator
who also has extensive aerosol knowledge and expertise. He has made presentations
at National Societies on the fire and explosion hazards associated with aerosol
and was the first to publish a peer-reviewed paper on aerosol failures. He now
leads the field in the number of peer-reviewed papers on aerosol failures as he
continues to publish. One of his papers deals specifically with failure analysis
when part or the entire failed components are not available.
©2008 CHEMAXX, INC