Respirators are assigned for workers at a series of different tasks until air testing establishes that lower protection factors are required. This classification includes the Bullard Series 77 and 88 helmets, the Clemco Apollo Series, and similar helmets by Northstar, MSA, and other manufacturers. Each consists of a rigid helmet with a small plenum installed above the forehead. A continuous flow of air comes down past the face of the worker, and discharges through a cloth muff around the neck and under a cape. Both systems include a separate mask which seals around the face of the blaster, also shrouded under a heavy hood.
Air enters the mask and discharges out an exhalation valve mounted on the mask.
The mask is maintained under positive pressure at all times relative to the surrounding atmosphere. Thus, a high level of protection is afforded to the wearer. Mini-enclosures with restrained airflow will usually keep two and possibly three men below this limit depending upon the rate of paint removal by the blasting operations. For bridges enclosed in this fashion, more men can legally work than will be able to blast at typical tank projects. All of these issues must be discussed in the employer's mandatory compliance program.