A total of 3.3 million employees - about three percent of all private-sector employees - wear respirators on the job, either voluntarily, to meet regulations, or in emergencies, according to a 2001 study by the Bureau of Labor Statistics.

Respirators are used in about one in ten private industry workplaces, and about half of the time they are used by employees on a voluntary basis only.

About 40 percent of these worksites do not offer employees specific training on respirator use, relying on manufacturers' instructions or contending that training is not needed. In 59 percent of the workplaces, employees are trained to understand the use and limitations of the respirators they wear.

Paint vapors and dust are the most typical reasons for wearing air-purifying respirators, while paint vapors and solvents are the most common reasons for wearing air-supplied respirators.

Air-purifying respirators, most often dust masks, are worn in 95 percent of worksites where respirators are used. Air-supplied respirators, most commonly self-contained breathing apparatus, are used in 17 percent of the worksites.

Dust masks are the most common type of air-purifying respirator used - accounting for more than 71 percent of all use. Less than 15 percent use powered air-purifying respirators.

Here's how employers make decisions about respirator use:

• 34 percent depend on written programs adopted by management;
• Almost 23 percent say that supervisors decide based on employee input and job characteristics;
• 22 percent report that employees decide based on job characteristics;
• 20 percent report that respirator manufacturers' written instructions determine how respirators are used.