Bomb disposal deputies with the Calaveras County Sheriff’s Office helped to safely destroy about 2,500 century-old explosive detonators called blasting caps by blowing them up inside a blast-proof trailer in early March in Amador County, a sheriff’s sergeant said Tuesday.

Blasting caps are small, primary explosive devices used to detonate larger, more powerful secondary explosives like TNT, dynamite or plastic explosives. Blasting caps have been used in commercial mining, excavation and demolition.

One blasting cap can cause serious injury or death all by itself if mishandled, said Sgt. Greg Stark, of the Calaveras County Sheriff’s Office.

Someone in Amador County was in the process of demolishing an old building in an unspecified location and found the blasting caps, Stark said, adding it was an undisclosed location in Plymouth, a town of about 1,000 residents.

“At this time we are not releasing the location,” Stark said. “We don’t want persons scavenging the area until the restoration project is complete.”

Six sworn deputies with the Calaveras County Sheriff’s Office are trained to handle explosives, improvised explosive devices, and post-blast investigations. At least two of these deputies went to Amador County with the blast-proof trailer on March 9 to deal with the 2,500 blasting caps, which were determined to likely have been manufactured more than a century ago in 1918.

The blasting caps were so old they had deteriorated to a point where they had become possibly unstable and could explode unexpectedly, according to Stark.

The Calaveras deputies cleared an area around the blasting caps and moved them into the blast-proof trailer. Then, they hauled the trailer to an unspecified rural location and blew them up using 17 counter-charge explosions over the course of two days. 

Blowing up the blasting caps was the only way to render them safe, Stark said.

Deputies believe the 2,500 blasting caps were manufactured by Atlas, a company that used to operate out of Oakland and sold blasting caps over-the-counter from 1918 to 1934 for mining operations, Stark said.

The explosive material in the old blasting caps was identified as mercury fulminate/potassium chlorate, Stark said. They were found stored in several cardboard containers.

There are thousands of old mines and mining operations in the Mother Lode, including more than 850 old mines in Calaveras County, more than 1,250 in Amador County, and more than 1,100 in Tuolumne County, according to the U.S. Geological Survey and The Diggings, a trademarked resource for locating where mining claims are and have been.

The Calaveras County Sheriff’s Office and members of its Explosive Ordnance Disposal Unit are reminding people that all explosives should be considered dangerous, especially ones that are old and showing signs of deterioration. Based on what happened three weeks ago in Amador County, they are now offering tips specific to blasting caps.

• Do not pick up or handle blasting caps. The same goes for tins and other containers used to store blasting caps. Friction caused by opening a container could cause detonation.

• Fuse caps contain explosives like mercury fulminate, lead azide and lead styphnate. Fuse caps are often small metal tubes, 1 to 2 inches long and a quarter-inch diameter. Fuse caps can detonate if subjected to heat, shock or static electricity. Old fuse caps with crystallization show they are deteriorated and they are very dangerous.

• Electric blasting caps are similar to fuse caps. They have two insulated electric wires attached to one end. Electric blasting caps can be detonated due to heat, shock, static electricity, radio frequencies, and electromagnetic radiation.

• Non-electric blasting caps are safer than fuse caps and electric blasting caps.

Contact Guy McCarthy at or 770-0405. Follow him on Twitter at @GuyMcCarthy.

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