On a snowy morning last month in New Hampshire, an officer with the Manchester Police Department advised workers in a hotel lobby on what to do if they find opioids in guests’ rooms.

Of particular concern was Carfentanil, a synthetic opioid that’s 5,000 times more powerful than heroin and 100 times more potent than its derivative, fentanyl, which is lethal on its own and accounts for a surge in fatal overdoses nationwide.

Carfentanil — it’s used to tranquilize elephants — is deadly to humans at 0.02 milligrams, an amount akin to a speck of dust. Therein lies the added danger: the substance is difficult to see, sometimes resulting in accidental exposure that could be harmful to anyone who runs across it.

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