— “Back up, sir!” shouted Kenny Kiefer, a Fire Department battalion chief, his N95 mask muffling his words.

Alarmed, Chief Kiefer stepped back and thrust out his palm.

Now with coronavirus infections sweeping through the region, the emergency medical workers of Paterson, a poor, industrial city in the penumbra of pandemic-stricken New York, are working in a new, upside-down reality: Don’t go in a home, don’t touch the patient, and don’t take anyone to the hospital, unless absolutely necessary.

Chief Kiefer’s job was to assess possible Covid-19 cases, to determine whether a specialized ambulance with E.M.T.s in hazmat suits should follow up.

ImageKenny Kiefer, a Fire Department battalion chief, left, spoke to a man who called 911 because he had been having trouble breathing.Day and night, ambulances crisscross the streets of Paterson, the eerie silence of a once-raucous city shredded by siren shrieks so pervasive it sounds as if the city is under attack.

With colossal public housing projects and families crammed into sagging, multiunit homes, Paterson is a densely populated city of nearly 148,000.

McDermott, the exhausted chief of the Fire Department.

There were 576 confirmed cases of coronavirus infection in Paterson as of late Wednesday afternoon, a number constantly rising.

Joseph’s University Medical Center in Paterson is being hammered with patients; the 650-bed hospital, currently handling about 100 Covid-19 cases, is searching for outside locations for more beds.

Despite the efforts of the E.M.T.s to keep moderately ill people at home, nearly 80 percent of ambulance calls for suspected coronavirus have been serious enough to require transportation to the hospital.

A few weeks ago, deceived by dispatch calls for “leg pain” and “sick person,” E.M.T.s ran into homes wearing only masks and gloves.

The Paterson Fire Department allowed New York Times journalists to accompany a 12-hour shift of E.M.T.

7:30 a.m.The shift beginsOn a chilly spring morning, nine E.M.T.s assigned for the day to answer only possible coronavirus calls reported for duty in an inflated tent in front of the Lakeview Firehouse.

The tent is a designated decon — decontaminated zone — where freshly sterilized hazmat gear is stored.

Deputy Chief John Bradle, 56, a brisk, bald 24-year veteran of the department, issued the day’s orders.

(The Paterson Fire Department oversees emergency medical services; nearly all 275 firefighters are certified as E.M.T.s.).

While two-person ambulances respond to gunshot wounds and heart attacks, crews of three now ride the ambulance — known to the crews as the “bus” — to calls that are designated “P.U.I.”: person under investigation for Covid-19.

The rules: One guy sits in the back, always in a full hazmat suit.

in full hazmat.

Chief Bradle underscored this new slow-your-roll regimen: “The goal is to get an oral R.M.A.” — refused medical assistance.

As crews headed out to begin the shift, Chief Bradle said to each man: “Be safe and stay safe.”.

in full hazmat hastily told her to remain on the porch.

Neighbors leaning over rowhouse staircase railings watched as two men in shiny beige hazmat suits, safety goggles, a mask with disposable bubblegum-pink filtration disks, eggplant-purple gloves and knee-high green chemical-resistant boots with lemon-yellow soles, headed into an apartment building.

Six minutes of ultraviolet light should clean the interior properly, but department protocol requires 20 minutes.

During that 24-hour shift, the E.M.T.s and three designated coronavirus vehicles went through the full decontamination process a total of 28 times.

Several days later, with the number of coronavirus calls surging, during the 24-hour shift four vehicles were decontaminated 51 times?

In mid-January, Chief McDermott, a 25-year-veteran of the department, was already worrying about the virus stalking China.

But Chief McDermott, 47, a father of three daughters who is married to a hospital labor and delivery nurse, is a not-to-be-argued-with, paramilitary kind of a guy who obsesses about safety.

Even during the shift, men who should have donned hazmat hadn’t yet memorized the latest edicts, and so entered homes with suits that would rip when they squatted to lift a patient — potentially leaving them exposed.

But at least everyone working on a Paterson ambulance, whether answering a heart attack dispatch or a coronavirus call, is equipped with a high-density protection suit or top-level hazmat.

Combined with the super-decontamination they undergo after each coronavirus call, Paterson’s E.M.T.s have far more protection than many departments offer.

“We watched Bergen County” — which has the highest rate of confirmed cases in the state — said Chief McDermott, “and we said, ‘Forget that.’”.

As Chief Kiefer was about to head to a fresh call, a frightened man approached, holding a can of a Lysol bathroom foam spray: Would it protect his family.

Chief Kiefer told the man to check the website of the Centers for Disease Control and Prevention, which links to a list of household cleaners that may be effective against the virus.

Joe’s paramedics in hazmat suits did C.P.R.

Many grew up in Paterson or nearby.

To get a laugh, two guys in full hazmat gear will start twerking.

After a hard call while being encapsulated in hazmat, guys often get sweat-drenched and even claustrophobic?

They include deputy and battalion chiefs, captains, firefighter E.M.T.s and dispatchers.

At the end of a tour, Marvin Cruz, Paterson born and bred, who has a 6-year-old and two teenagers, goes to the side door of his home, takes off everything but his underwear — “Free show for the neighborhood!” — stuffs his clothes in a biohazard bag, steps inside and dashes for the shower.

opened the ambulance doors.

8:15 p.m.Just one more callA regular two-man ambulance radioed for a coronavirus-ready bus: The “distressed breathing” call at a dialysis and rehabilitation center turned out to be a patient who clearly needed to be hospitalized.