NYPD narcotics officers have stopped doing field tests on heroin because of the dangers of accidental poisoning from fentanyl, a powerful synthetic opioid that can be found mixed with the drug, Police Commissioner William Bratton said Friday.

Instead, narcotics units are sending the samples directly to better-equipped police laboratories — a new policy that the Suffolk County Police Department said it also has begun in the interest of officer safety.

“It has become such a serious problem … the prevalence of fentanyl, that we have drastically changed our field testing procedures for the safety of our officers,” said Bratton, who expressed his “high concern” about the scourge of heroin laced with fentanyl, which greatly enhances the potency of drugs.

Officials have attributed numerous heroin overdose deaths in the city and on Long Island to the dangerous effects of fentanyl.

While NYPD narcotics cops are equipped with protective gloves and masks, officials are worried that ingestion of airborne particles of fentanyl that are released during the field tests can harm the officers, chief of detectives Robert Boyce said.

In a telephone interview, Suffolk County police commissioner Timothy Sini said that Suffolk officers also are being told to send heroin samples they purchase in undercover buys directly to the police laboratory.

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If the lab test finds a dangerous amount of fentanyl in the sample, police then apply for an emergency search warrant to raid the location where the drugs were purchased, Sini said.

On Thursday, Bratton hosted Sini at a special meeting during which the problems of fentanyl and officer safety were discussed. A special video on the topic was shown, which the SCPD began using Friday to educate its officers, Sini said.

The danger of fentanyl-laced heroin recently was underscored in New Jersey, where two officers almost died this year after they inhaled an airborne plume containing the synthetic opioid, Boyce said. Fentanyl is produced in Mexico and smuggled into the United States, where it is combined with South American or Southeast Asian heroin, according to Boyce.

Data released by city health officials in April showed a large increase in the number of drug overdose deaths in the five boroughs in 2015 compared to the previous year, with a larger proportion attributed to fentanyl. Of the 886 deaths, 15 percent involved fentanyl, compared with fewer than 3 percent in 2014.

State records show that in 2014, Suffolk County had 111 heroin overdose deaths and Nassau County 58.

Sini said there have been well over 100 opioid overdoses in Suffolk this year, although police use of the antidote naloxone has saved numerous people.