Caution:
Welding / Brazing in Confined Spaces
If it is difficult to get into the workspace or there are any confining features of the workspace, don't fire up the torch.
If you have to wiggle into a spot to get close enough to your work, don't fire up the torch.
If there is only one way out of the workspace, don't fire up the torch.
You should never to weld, braze, cut metal in a confined space unless you are certified to do so. OSHA 'permit required confined space' standard must be followed when work is performed within a confined space. The OSHA standard mandates continual testing the air, coordinated entry to the work area, rescue provisions, and the training of the workers on the hazards.
In addition, other federal, state and local building regulations may require special precautions to safely weld, braze, cut metal in a confined space. This type of work could require forced draft ventilation, personal filter respirators, SCBA air masks, air hoods or hose masks. You should never try to weld, braze, cut metal in a confined space unless you are certified to do so.
If there is any doubt, don't fire up the torch!
For more information, consult the American National Standard Z49.1, "Safety in Welding and Cutting".