Loft use

[raypickett]

Other than the obvious is there any danger of live steam on the loft

[Big Jim]

Lack of ventilation might make the atmosphere a bit unpleasant.

[daan]

It depends.. If you have wooden flooring and run prewar live steam locomotives with an open fire with a meths burner, then I wouldn't think the loft is a good choice. If you run a modern live steam with a single flue gasburner the risks are low, as long as you have ventilation and stay focussed on what you're doing.

You would need to protect the floor though against oil stains and I would advise getting a CO2 fire extinguisher. Not a regular powder extinguisher, since they mostly contain salt and this gives more harm then doing good when you use them. A good fire blanket can do the job as well, as long as the flooring is not made of planks (they have airholes and a blanket can't kill the fire that way)

The biggest risk is in using burners on fluids and solid types of fuel. When a derailment occurs, fluid can leak out and set a lot in flames in a short time. Dry timber from the flooring will suck up the fluid before it burns and this wil easily get a serious fire. So no open fire and no possible leaks of flammable liquids or solids, then it should be ok.

Ventilation is a simple window or roof vent which you can open. When you leave the stairdoor open, fresh air will flow through and since it's just a small fire, this will be enough. Even in the case CO will form, it is heavier then air, so it will not fill the loft when you leave the door open. Your cat on the groundfloor might have a problem, but you don't

The last thing is moisture.. A 300cc boiler will make about 5 cubic metres of water vapour (it expands 1600 times) and that needs to go somewhere. That is something you need to find out yourselve if you can get rid of that, though it's about equivalent to a drying rack with clothes drying.

[raypickett]

I do spprecate the comprehensive answer---thanks Ray