Five a.m. Sunday morning is too early for trauma. But in emergency work, Sunday morning is still Saturday night, and when the call comes over the radio for an “injury minor,” we respond.

With noncritical injuries, I don’t bother with lights or sirens, especial ly at this hour, with the neighborhood windows all dark. But what comes over the radio and what you get in front of you are two different things. When we arrive, it’s clear that someone was speaking conservatively when he called 911.

Our man is standing on the corner of Nostrand and Beverley – not a nice place in daylight, much less in the dark – in front of a gloomy bodega, with his pant leg rolled up and what looks like a plastic bag tied like a tourniquet around his thigh. Blood is streaming down his leg and over his shoe.

“What happened?” I ask, opening the ambulance doors to get him inside.

He looks at me like I’m crazy. “What happened is I’m bleeding out!”

I take a deep breath, and the alcohol fumes coming off him surround me like a toxic cloud.

“Sir,” I say, “you have 12 pints of blood in you. I see about half a pint on the ground. Step into the ambulance. Use your good leg.”

He shouts obscenities at me as I arrange him on the stretcher, while my partner Bronson tries to find out from bystanders what happened. A scruffy man with a brown paper bag tucked in his coat pocket says a guy named Rodriguez cut this man, named Duane, with a machete.

“Great,” I say.

“Dominican,” the man says. “Big machete.”

I peel away a flap of plastic bag to find a 3-inch gash across Duane’s knee. It’s pulsing rivulets of bright red blood that clots in thick ropes down his calf. Clotted blood is good: It’s the body’s own bandage, covering the wound as well as keeping more blood from flowing out. I press a wad of gauze to the injury and wrap a bandage around it. Then I cut off the ridiculous plastic-bag tourniquet.

There are two problems with this tourniquet. First, it isn’t tight enough. It should be cloth, and the ends should be twisted with a stick and secured with a knot. This plastic-bag contraption is actually forcing blood pressure to build in the lower leg – much like what a nurse does with that blue rubber band around your arm when she searches for a vein. A real tourniquet should be tight enough to cut off blood from the wounded limb altogether.

Second, a tourniquet should only be used if the bleed is life-threatening and the limb below it is unsalvageable and will be removed by a surgeon, as in the case of a partial or fully amputated limb. (Readers might recall a British nurse using a man’s belt during the Staten Island Ferry crash.) Preventing blood from exiting a wound also prevents the blood already in the limb from flowing back to the heart. Unoxygenated blood is dead blood, and once a tourniquet is loosened, the dead blood will reenter the bloodstream and cause damage, especially upon reaching the heart, which may go into cardiac arrest.

Finally, when a tourniquet is applied, the injury is usually so severe that the time of its application is written by emergency workers in giant numbers on the patient’s forehead, usually in his own blood. The doctors who end up treating him will need to know this.

So it’s a good thing this tourniquet is a joke. I cut it off and fling it to the ground. Curiously, I find another one, also made of plastic, below the wound site, hidden under the clotted blood.

By now, blood has collected on the floor of the ambulance. I press more gauze onto my previous dressing and wrap it again with bandages, then press the man’s femoral artery, located in his groin, with all of my fingers to staunch the flow of blood to his leg while allowing blood to return to his torso via his veins. After a few minutes, I let go and peel off my gloves to do the paperwork.

“ETOH,” I write in the comments section. It’s the chemical name for alcohol, and among emergency workers is the polite way of communicating to the hospital staff that the guy’s a drunk without advertising it.

“I can’t be getting into this s— at 39,” Duane slurs.

I check the bandage to make sure it isn’t bleeding through. “I agree,” I say.

He clutches his leg and stares at the ceiling lights like he’s been wounded in combat. But I’m not giving him any sympathy. He got himself into this mess.

At the hospital, a young intern comes rushing over, his eyes sparkling as he dons his gloves. Interns live for this. No sickness, no sorrow, no death. Just easy Sunday morning trauma.

Ms. Klopsis is an emergency medical technician for the FDNY. This column details her observations and experiences on the job. Some names and identifying details have been changed to protect the privacy of patients.