A safety alert if you have a previously used propane cylinder. Manufacturers of meth are using them to store a very dangerous substance called anhydrous ammonia, used to make the drug.

Anhydrous ammonia, typically used as a fertilizer, can also be used to make meth.

"It's very similar to propane, it's liquefied gas, they steal a little bit put in a propane bottle and discard it when they are done," said Don Schlarb, owner of Old Town Propane.

Even though police say it’s rare, Schlarb had one show up at his store a couple of years ago.

"I had an elderly man bring us a bottle he had bought off the street for $5, we cracked the valve," said Schlarb.

He immediately knew something was wrong.

"I got tunnel vision and I needed to get out in the air real quick or I was going to be unconscious," he said.

He'd been exposed to the toxic gas.

"There's inherent dangers when you mix solutions in a cylinder and with the residue of propane in a cylinder, there could be a reaction," said Captain Scott Smith with the Colorado Springs Fire Department.

Which why propane users should pay attention to one key warning sign. If a valve stem of a propane cylinder comes in contact with anhydrous ammonia, it will turn a blue-ish, green color."

A color Schlarb looks for now on the valve of every cylinder he handles.

"It's probably the most dangerous thing I can think of in the propane industry," He said.

His best advice, always know where the propane cylinder you use came from. Never buy one off the street and never use one that's been abandoned.

Meth production here in the Colorado Springs is down. Police say less than 10-precent of the meth used here is actually made in the here. So far this year there have been five meth lab busts and none of them have been labs that used anhydrous ammonia.