Several people in the past couple of days have e-mailed and PM’d me with questions about their own situations where either their significant others or landlords have not allowed them to cut holes in walls or ceilings to allow ventilation. They still want to work safely and have asked me to help them resolve this issue.
As I’ve mentioned many times, a hood or workstation enclosure is the best possible way to capture and exhaust fumes from torch working, but there are times when it isn’t possible to have a perfect solution.
In these cases, I like to see a complete room air change every 5 minutes. I define a room as the entire space where the torch(es) are located, not just the local area inside a larger room.
For example: a studio space that measures 40 feet by 50 feet with 16 foot ceilings has 32,000 cubic feet of air in it. To change the air every 5 minutes, divide 32,000 by 5 and you get 6,400 CFM. The average box fan moves around 2,000 CFM (on high), so you will need at least 3 box fans directed outside, plus an equivalent amount of fresh air coming in from outside (a minimum of 10 feet away from the exhaust).
In order for the fans to work efficently, the entire opening where the fans are located must be sealed so that that air cannot backflow into the studio space. Cardboard, plywood or other building materials should be used to construct a door/window seal that ensures that air cannot backflow into the studio space. Simply placing a fan on high in an open door way does not exhaust a space. Do not use the fans to draw air into the space, use the fans to exhaust only. It will also be a good idea to have several fans located in the space to move air from the open fresh air intake towards the exhaust, being sure that it flows over the workspace area.
Please note that this is NOT a pefect solution, only a temporary fix. The only truly safe way to exhaust your torch is with a dedicated local exhaust ventilation system.