134a Explosion Investigation |
134a Explosion Investigation |
DOT Regulations LinksButane Cigarette Lighter Explosion
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134a Refrigerant ExplosionThe owner of an automobile was attempting to recharge the air conditioning system using a kit sold for that purpose. The refrigerant was tetrafluoroethane, commonly called Refrigerant 134a. The common use of "Refrigerant 134a" to identify "tetrafluoroethane" is not linked to any particular product or manufacturer in the context of this investigation summary. The recharging product, in addition to containing Refrigerant 134a, also contained lesser amounts of lubricants and sealants. The complete mixture was packaged in a Department of Transportation (DOT) 2Q metal container.
The individual attempting the recharge testified that he placed the container of 134a product on the engine valve cover for a short period of time while the engine was running. The container of 134a was never connected to the A/C system. Per testimony, shortly after the engine was turned off, the bottom of the container exploded off creating a rocket that hit the individual in the eye causing the loss of the eye. This is called a "mechanical explosion" and the mode of failure is a "deformation failure." It may seem illogical that the container exploded after the engine was turned off, but water-cooled, automobile engines get hotter for a short period of time after they are turned off. Experiments confirmed that this continued heating does in fact take place. Experimental
measurements determined that the vapor pressure of the contents (134a plus lubricants
and sealants) was 200 psig at 130°F. This exceeded the maximum pressure (180
psig) allowed by DOT Regulations by 20 psig. The pressure versus temperature behavior
of the product tracked that of pure tetrafluoroethane almost exactly, as one would
expect. The vapor pressure of pure 134a is 199 psig at 130°F.
Per DOT Regulations, contents with 130°F pressures between 180-200 psig need to be packaged in special DOT-E containers, not DOT 2Q containers. Experimental heat-to-burst tests demonstrated that the product exploded below the minimum burst pressure (270 psig) required by the DOT more often than they exploded above the DOT minimum. One exploded as low as 200 psig. These experimental findings led to several scientific publications in a peer-reviewed journal and conference.
Test methods developed at an earlier time by Chemaxx and applied to this investigation were challenged under Daubert in Federal Court. The Court ruled that most of the test methods satisfied the Daubert criteria. Chemaxx-funded research conducted in parallel to the legal case led to the discovery of a correlation between the strength of the container bottom and its explosion temperature in the heat-to-burst tests. This method has been published in a peer-reviewed, scientific journal. The correlation methodology makes it possible to determine the explosion temperature of a container that has already exploded, provided that the bottom can be found and it is not too severely mangled from impact. The main issues involved in the case were whether the container and its contents met DOT specifications. Measurements showed that the 130°F pressure of the contents exceeded the maximum of 180 psig for a DOT 2Q container. Experiments also showed that the DOT 2Q containers exploded in heat-to-burst tests at pressures below the minimum DOT requirement (270 psig) more often than they failed above that minimum pressure. This was experimentally determined to be due to a lack of safety margin in the strength of the container bottom. However, the case settled prior to trial without any admissions or legal decisions concerning these issues. The methods used in the investigation included:
The above research led to a peer-reviewed scientific publication in ASM's Journal of Failure Analysis and Prevention, April 2006. It also prompted a Petition to the Department of Transportation by Dr. Fox. To read the DOT Petition, Click Here Dr. Michael Fox of Chemaxx, is accredited in Aerosol Technology by the Center for Professional Advancement as well as the British Aerosol Manufacturers Association, and certified by the DOT in the transportation of hazardous materials. (The DOT regulates aerosol containers and the products that can go in them). Dr. Fox is a Certified Fire & Explosion Investigator who is also an aerosol expert. He made presentations at national societies on the fire and explosion hazards associated with aerosols 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. |
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