We get a call for a “man off the roof” in the Boro Park section of Brooklyn. He is in a driveway between two houses where renovation work is being done.

Bronson doesn’t for a minute doubt the legitimacy of this job, and neither do I. It rings too true in this neighborhood buzzing with active real estate sales and frequent home improvement. “Betcha he’s an illegal,” I say.

Sure enough, we find a Mexican day-laborer kneeling on the concrete with his head to the cement. We often see illegal aliens standing on street corners on Fort Hamilton Parkway by Greenwood Cemetery and along 65th Street in Boro Park, waiting to get picked up by contracting crews for a day’s work.

Holding the guy’s head in in-line stabilization is an off-duty Hatzolah EMT, from the Jewish volunteer service in Brooklyn. I assume the owners of the house are Orthodox and dialed Hatzolah, while the construction boss dialed 911. “Found him in this position,” the Hatzolah guy says.

I can already see the patient’s outcome will not be good: blood is gushing from his misshapen head, and bits of brain matter lie scattered on the ground. “Anybody see what happened?” I ask the other workers. “Anybody know who he is?”

The site boss says the patient was working on the roof beams when he slipped and plunged 20 feet to the ground. When I ask for his name and age, the other Mexican workers all shake their heads and say nothing.

I open the patient’s eyelids and shine a light in his eyes. His pupils are dilated and non-reactive. He’s making snoring respirations and blood is coming out of his nose. I count his breaths at six a minute, which is slow enough to be considered respiratory failure. The Hatzolah guy says, “Bag him! We gotta bag him!”

Bronson starts shouting orders. “Cervical collar! Gimme a trauma dressing! Get him onto the board! Now … one, two, three — up!” We place the patient on the stretcher and roll him into the ambulance. I secure the trauma dressing to his head with cling gauze to try to staunch the flow of blood, but of course it doesn’t work. The Hatzolah guy tries bagging, but not a lot of air is reaching his lungs — there’s inadequate chest rise and fall. And to think he started his day just standing on the street corner waiting for work.

Medics arrive, two guys we know. “Whaddaya got?” they ask, coolly. Nothing ruffles them. I explain the situation, and they calmly attempt to intubate through the patient’s clenched teeth while Bronson gets behind the wheel and hits the pedal. They can’t get past the clenched jaw, so they start an IV and call FDNY telemetry for authorization to give the patient valium via IV to get him to unclench.

As we head to Lutheran, I note the patient has not moved his body. My feeling is that he will never regain consciousness or breathe adequately on his own, and will be placed on life support. The problem is that, unless a family member is around, or unless he has advance directives regarding life support should he become too incapacitated to make his wishes known — both of which are unlikely — he will stay on life support indefinitely. Or become a cause célèbre for anyone’s political convictions.

One of the medics draws up the valium and gets ready to give it.

“Sam, you forgot the lidocaine,” his partner says. This is to reduce intracranial pressure before tubing someone with severe head trauma. The first medic says, “Thanks, George,” and pushes both drugs. Then he successfully tubes the patient, and I start bagging. Adequate chest rise and fall. Hopefully, I’m bringing some oxygen into his bloodstream. At least, I’m conditioned to think this. But a part of me also thinks: What for? He left part of his brain on the ground in the driveway.

En route, Bronson gives a notification to Lutheran, and once there, the ER staff takes over. The triage nurse taps on her computer and asks us if the patient has any ID.

“ID?” I say with a laugh, even though deep down I feel queasy, carsick, the way I always feel when something happens on the job that makes the thin veneer of reality start slipping.

Somewhere in Mexico, a woman will live the rest of her life wondering what ever became of her son.

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