Producing hydrogen sulfide at home - how dangerous is it? When I was a kid, I used to go to the pharmacy to buy sulfur and iron powder, then mix it together and heat it until it starts to react into iron sulfide. Put a chunk of iron sulfide into some vinegar, and you get a room smelling badly of rotten eggs. This experiment was also described in some "chemistry for kids" boxes from the 80's.

Now I'd like to do this experiment with my son, but in the meantime I learned that hydrogen sulfide is a very potent poison, even more poisonous than hydrocyanic acid. For this reason, I'd like to set up some precautions.

Of course I won't do it in a closed room, and I won't let my son breathe in much of the gas.

The gas can be smelled long before it starts to get dangerous, so I think it should be pretty easy to use an amount of sulfur and iron that will cause the characteristic smell, but at the same time is guaranteed to not cause any danger. So, I'm looking for some quantitative estimation:

How much iron sulfide would be enough to create a dangerous amount of hydrogen sulfide? To make the calculation easier, let's assume we grind the iron sulfide and use a stronger acid than vinegar, so that all of the gas will be created almost instantly.

If possible, it would be great to have two estimations: one of the beginning of the "danger zone", and one of the beginning of the "lethal zone". According to Wikipedia, the gas starts to smell at $\pu{0.00047ppm}$, the danger zone starts at about $\pu{10 ppm}$, and at about $\pu{320 ppm}$ it can be lethal.
On the question as to how dangerous is H2S let me detail some facts that I find problematic. Here is a good paper. 

I summarize some of my findings:

First, H2S after initial exposure can deaden your sense of smell (10-minute exposure at 50-100 ppm impairs the sense of smell). So, one may not really have an accurate conception of the magnitude of one's time exposure to the gas.

Second, skin exposure may be a path to ingestion, especially if moist I suspect. Note, some sources actually disagreed on skin exposure poisoning of Hydrogen sulfide with one study alluring to skin toxicosis from high concentrations over a long period. 

Third, following a significant exposure event, the very fact that you are still alive should not be comforting. People having incurred a lethal dose may be a de facto walking dead with a slow hourly progression to death.

Fourth, the ppm considered fatal for H2S is not that far removed from some known very toxic gases (like HCN). However, my opening reference doubts if one can even assign accurate figures on ingestion via the lungs. Here is an extract addressing dosing level ranges:


  Findings in the canary, cat, dog, goat, guinea pig, rabbit and rat (2) are consistent as to the effects of hydrogen sulfide: at 150-225 mg/m3 signs of local irritation of eyes and throat after many hours of exposure; at 300-400 mg/m3 eye and mucous membrane irritation in 1 hour and slight general effects with longer exposure; at 750-1000 mg/m3 slight systemic symptoms in less than 1 hour and possible death after several hours; at 1350 mg/m3 grave systemic effects within 30 minutes and death in less than 1 hour; at 2250 mg/m3 collapse and death within 15-30 minutes, and at 2700 mg/m3 immediate collapse, respiratory paralysis and death. 


Viewing all these together, if one has a choice to avoid working or experimenting with the gas, I would do so.