Any farrier who swaps propane tanks with retailers should keep an eye out for valves and fittings that have been compromised while making methamphetamine or meth.

Manufacturers of the illegal drug use the tanks for storing and using anhydrous ammonia. According to the National Propane Gas Association (NPGA), anhydrous ammonia damages the brass valves and fittings.

“This deterioration will lead to cracking of the valve body or its components and can ultimately result in a violent, unexpected expulsion of the valve from the cylinder, causing personal injury or death,” according to a safety alert from the NPGA.

One of the most recent cases of alleged propane tank use in the manufacture of meth occurred in Sandwich, Mass. (Thanks to Sagamore Beach, Mass., farrier Nick Denson, who shared a video from WCVB-TV on Facebook.) Although retailers are trained to recognize the indications that a propane tank contains or has contained anhydrous ammonia, it’s never a bad idea for farriers to know as well.

“One of the telltale signs is blue discoloration around the valve or the stem fittings,” explains Sandwich Fire Department Capt. James Huska. “It’s definitely noticeable.”

Other signs to watch for are tank distortion and a strong, pungent odor of ammonia on or near the cylinder. It must be noted that Sherwood valves contain a green-coated valve stem. In addition, a green thread sealing compound is used on some valves. These should not be confused with those that have been exposed to anhydrous ammonia.

If you suspect that a tank contains or has contained anhydrous ammonia, do not attempt to move it and immediately call 911.