Today, I watched a homeless man die on 16th and Valencia.

I was eating a salad, 15 feet away. He was lying on a cardboard mat, with his head sliding off a makeshift pillow made of some clothes in a plastic produce bag.  I sat and watched him for a minute, wondering if I should call the police.

It was hot, and he was shirtless. At the least, he'd wake up with a nasty sunburn, I and another onlooker thought. I decided he was probably really tired, and as he wasn't in anyone's way, I figured I should just let him sleep.

What I didn't even consider was that he was most likely dehydrated. Severely. And, as it turns out, fatally so.

His arm was bouncing around spasmodically. I thought he might be doing it on purpose, maybe he was listening to some imaginary drum beat in his head. Turns out, I was watching him convulse. Probably at the very moment that his life was leaving his body.

Someone did finally call the police. Not sure who. Several people walked by, seeing him, and shrugging their shoulders. I did the very same thing, even though I did not think of him as a scourge the Mission would be better off without.

And I truly believe that most people walking by would have stopped to help if any of us had thought he was in real, immediate trouble. The truth is, I didn't know what to do, and I doubt most people do. Calling the cops or 911 seems extreme.

Firefighters were the first to respond, and after rolling him over and starting CPR, even giving the defibrulator a try, they quickly realized it was too late. They put a yellow plastic emergency blanket over him, and covered his head with his jacket.

Then the cops came. And the coroner. After I gave my statement to the cops, I had to go pick up my little kids from school.  By the time I came back, maybe half an hour later, the whole scene had been cleared.

Frankie Bizo — or something similar, as a neighboring merchant told me he was called — was taken off to the morgue. He was 67 years old, and considered a serious alcoholic. I heard he turned up in the neighborhood, fully cleaned up and looking good a couple of times. But then quickly fell back into his old ways, and was back on the street, where he had presumably been for years.  He has a sister with kids in Oakland.

All that was left of him on the street was the dirty cardboard mat, a dingy, black jacket and crumpled, red T-shirt,  a couple of uneaten cartons of decent looking leftovers, and an empty school-size milk carton.

I called an aquaintance of mine from the Mission Neighborhood Health Center. They were wonderful. They walked right up from their headquarters on Capp Street, and helped me ask around about the man's identity.

The day of the death, they had just been on rounds with the new Mission Community Ambassadors. As part of a brand new pilot program active in a couple places around the city, a handful of members of the loosely connected 16th Street BART Plaza community now have the paid job of just checking in on people, making sure they are OK, safe, and know where they are going. Tourists, local residents, and homeless alike. Pretty amazing program. But they had turned down Valencia Street before crossing, and didn't see poor Frankie in time.

A sad, eye-opening moment among many in the Mission. But the one lesson I have learned, from Laura Guzman of the Mission Neighborhood Health Center, is that it's OK to just tap a homeless person on the shoulder and ask if he or she is OK. They won't likely mind, even if they were sleeping. And be aware on hot days that really drunk or sick people may not realize how dehydrated they are, and that can have fatal consequences.

You can also now reach the Community Ambassadors via 311.  At least until the end of August, when the program loses its first round of funding.