Tetryl exposure: forgotten hazards of antique munitions

Tetryl, or 2,4,6-trinitrophenyl methyl nitramine, is an explosive similar to trinitrotoluene (TNT) and was used extensively during World War I and II as a detonator and booster in munitions [1]. Tetryl’s stability over time made it a desirable explosive for military applications. U.S. Post-WWII production was limited to one plant, and ended in 1973 [2]. Tetryl is still used internationally in land mines. Today the most likely contact with tetryl in the U.S. is workers involved in disposal, destruction, and cleanup of discarded munitions [3]. In 2007, the US Department of Defense proposed a beneficial use of this hazardous military waste, creating a novel plan to dispose of demilitarized tetryl as part of surface mining of coal. Surface mine operations usually involve drilling a row of holes that are filled with explosives (generally ammonium nitrate-fuel oil (ANFO)) to blast away the “overburden”. Handling of ANFO does not cause any know chronic disease [4] but that same safety does not apply to older munitions such as Tetryl.

In 1943 industrial hygienists determined that tetryl concentration of 1.5 mg/mg/m3 was considered to produce no health effects [4, 5]. The current OSHA permissible exposure limit [PEL] remains at 1.5 mg/m and has the [skin] notation [6, 7]. There is an “advisory” OSHA guideline for tetryl exposure, no other OSHA regulations exist [7]. Here we report the health symptoms and findings of 22 surface mineworkers exposed during a tetryl disposal operation in West Virginia, USA, and who then presented to the university clinic. The goal of presenting this case series is to emphasize the importance of recognizing previously known hazards before historic knowledge of safe handling older munitions is lost.

Following verbal encouragement from Department of Defense personnel, two surface coalmines in West Virginia participated in a novel beneficial use of tetryl. Tetryl munitions, stored at a demilitarizing facility, were loaded onto trucks and transported to the mine site. Workers employed by contract blasting operators were instructed to slowly add tetryl into the modern conventional blasting material (ANFO) as it flowed into the drilled holes. The goal was 1:10 tetryl to ANFO ratio. The loading, unloading, and pouring operations were all reported to be consistently dusty. Heavy equipment operators were tasked to remove the detonation-loosened overburden, and overburden removal was reported to be intermittently dusty, with pre-and-post detonation worker’s reporting yellow tetryl dust blowing into their breathing zones.

Before operations began, workers and explosives contractors were instructed that tetryl exposure was safe. No safety precautions were needed beyond those normally used for ANFO. Dermal and respiratory Personal Protective Equipment (PPE) were not recommended or provided to the workers. Workers did not shower on-site, and most wore their work clothing home. Nearly all of the patients in this cohort reported tracking tetryl dust into their vehicles and homes. Twelve of the workers also reported that they took empty WWII vintage ammunition boxes home as souvenirs. One asthmatic spouse reported increased asthma symptoms when washing work clothes during the period of tetryl use at the mine.

This tetryl disposal program ended after a tetryl-containing “shot” spontaneously ignited (EVENT A), generating a brownish-red cloud (presumed to be oxides of nitrogen) described to reach a height of 150 feet in February 2007. Dust from previously deployed tetryl remained on site for some time following. Before the operation ceased, the total tetryl exposure amount used in blasting (or lost as dust) was estimated to be 300,000-370,000 lbs. (136,000-168,000 kg) over the course of three months. Eventually, the military reassumed control of the remaining tetryl and removed it from the area.