Posts: 145
Estimable Member Apprentice Bladesmith (5yr)
You'd have to look at the combustion equation of propane to see what the gas balance is when burning propane.
There is actually a net positive of gasses produced. It's 6 molecules of gas in (1 propane and 5 oxygen) and 7 molecules of gas out (3 carbon dioxide and 4 water vapor). You produce more gas molecules through combustion than the forge consumes. Each molecule contributes equally to the pressure in your shop, so this combustion reaction actually creates positive pressure in your shop. Heating the shop with the forge also creates positive pressure simply because it warms the shop and heated gasses expand. If you have a tight shop you are slowly pushing gasses out of the shop through whatever openings there are in the walls, the water vapor and carbon monoxide displacing the nitrogen and oxygen...not good.
Burning coal would create even more positive pressure in a shop since the only gas consumed is oxygen but the two products (water vapor and carbon dioxide) are still produced. Even worse. Luckily the smoke (noncombustibles) makes people think about ventilation.
The real challenge is getting fresh (oxygen rich) air into your shop against this positive pressure. If you don't ventilate enough, you end up running your forge in an oxygen deprived environment and then you risk carbon monoxide poisoning (due to incomplete combustion). CO poisoning takes a while (sometimes weeks) to recover from...if you are alive to recover from it. I have other hobbies (running, skiing, the gym, keeping up with my kids) besides smithing, so I can't afford to have my hemoglobin tied up with CO, even a little bit.
In short, smiths shouldn't rely on the fire sucking fresh air into their shop. Most fires produce more gas molecules than they consume, so there is no "sucking." You need an easy way to convect those gasses out which will pull fresh air in through a window or open door. A hood would be great, but you still need an opening on the other side of the shop to let gasses in or the hood won't work well enough.
I just open my garage door and roll my forge outside or right up to the opening, regardless of how cold it is.
Steve
Note: Also remember that the propane is essentially being injected into the shop, so that's even more positive pressure. You must have an opening to let fresh air into the shop.
Posted : 22/12/2017 1:53 pm
