[PmbPhy (OP)]

Spraying someone with a fire extinguisher may seem like a good joke, but is entirely inappropriate when one can simply ask for an activity to be ceased.

I disagree. In Lisa's case she did that because she was scared it'd explode before she could remedy the situation. A halogen suppression system is installed and not something done by hand. One can push a button from the inside (that's how I set the question up in fact) and the gas is released and flows down. Its not dangerous at all. If that happened to me then I'd have plenty of time. I'd hold my breath and walk ten feet away where I'd be able to breath.

The only reason to release the fire extinguisher would be if an imminent threat was determined.

Which is exactly the scenario I set up to describe, i.e. Lisa experienced a clear and present danger. One of the facts of life is that two different people in the same situation can conclude different things "There are no WMD in Iraq" or "Yes there are!! fight fight fight!!!"

Nonetheless, a person would be required to safeguard others that were impacted by one's actions. 

Ideally yes. Not always possible in practice; Lisa felt she had a second or two to take action.

So, spray someone with a gas that knocks them out, one should get them to safety. 

Recall the OP = "The man is startled, stumbles, falls down ..."

Asphyxiation generally would occur over a couple of minutes, rather than seconds.  So, dragging the person to clean air should be more than adequate. 

Come on Cliff. Please don't expect people here to spend a day or two making 100% certain that they describe an actual event or include details so that you know everything about why something happened. I'm not going to do that. Especially since right now I want to spend my time saving real lives, not fictional ones. I said why he died, i.e. by accident and not by ignorance or lack of action. I'm a physicist not a sci-fi author.

Anyway, if a death occurred, I'd blame the death on the person using the fire extinguisher as a toy.

I never understood why people always think a person must be found and blame made. That's binary thinking and unwise in these cases. My sole intention was to describe a situation in which someone died because of a widespread and baseless fear.

I'll give you five minutes to do better. The longer you spend on it the more people really die in the US by suicide due to intolerable pain. On average that is now happening 32 times a day, i.e. more than once an hour. And I don't only spend time here and on that project alone.

I urge you to address only the problem at hand and as described. Sort of like watching star trek and not spending the entire episode explaining to the guy next to you that when someone uses a transporter they die and a new one is created at the beam location. Life's far too short for irrelevant nitpicking.

[PmbPhy (OP)]

Why don't propane torch explode when used as designed?

Could it have something to do with the control on the exit pipe, or the design of the torch?

Google it and learn if you'd like.

[wolfekeeper]

The fuel tank wouldn't explode. Often she would fail to light the vapour, but it's quite possible that it would catch. Then you'd have a flame coming out of the filler. To put it out, you just have to smother it, for example, a wet rag should work.

It depends on when the person last filled the fuel tank.  If the tank is full to the filling tube, then there may be a relatively small amount of oxygen/gas vapor in the filling tube exposed to air.

If the tank is say  1/4 full of gas, and 3/4 full of an air/gas mix, then it could have a vigorous reaction.  The tank itself being open to the outside may not explode, but could certainly shoot flames. 

No, that doesn't happen. The reason it doesn't is because the 'air' space in the fuel tank is above the flammability range for petrol, provided you're not down to the final few litres, then the 'air' space is saturated with petrol vapour and non flammable.

But if you're draining a tank down to work on it, you have to drain it and then air it out for a while, if you don't do that then it really can detonate.

[geordief]

What about meths?
I used a bottle today instead of firelighters.

A little bit at a time using the cap as it did not start in one go.

First the cap caught fire and it did not seem serious as I just blew it out but then the actual bottle caught the flame and overturned.

No harm was done (except to my fingertip) but I got the impression it was  very flammable but not as fierce as petrol (somehow "lighter")

Must remember to get those firelighters tomorrow :-)

[Bored chemist]

I'd blame the death on the person using the fire extinguisher as a toy.

Me too- if there was one.
But in the OP's story, nobody was doing that.

[Bored chemist]

then it really can detonate.

It almost certainly deflagrates but does not undergo a DDT.
https://en.wikipedia.org/wiki/Deflagration_to_detonation_transition