ST. LOUIS (AP) – The street version of fentanyl blamed in the deaths of thousands of Americans is also threatening police officers, forcing changes in long-standing basics of drug investigations, from confiscations to testing to undercover operations.

Overdose deaths have surged as drugs such as heroin, cocaine and counterfeit prescription pills are often laced with fentanyl, a man-made opiate so potent a speck the size of a few grains of salt can be deadly.

Fentanyl can be absorbed through the skin or inhaled if it becomes airborne. Police agencies ranging from small departments to the DEA are changing the way they do business to keep officers safe.

James Shroba of the DEA office in St. Louis says agents are even trained in “self-use” of the anti-overdose Narcan, just in case of accidental exposure.