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Cách Lựa Chọn Giữa Thiết Bị Cấp Khí Thở Di Động Và Thiết Bị Thở Động Cơ

Selecting Between Supplied Air and Powered Air en


Making the best choice for protecting your company's workers involves weighing several factors.

THE process of selecting appropriate respiratory protection can be as important and difficult as the decision about whether respiratory protection is needed in the first place. While the selection process can be complex and time consuming, the consequences of improper selection of respiratory protection equipment can be devastating.
Injury to employees, OSHA fines, and worker's compensation expenses are some of the more visible ramifications of improper respirator selection. Other factors that should be considered include a company's reputation, its ability to recruit good employees, and the costs related to employee turnover. And, of course, protecting an employee's health is the most substantial and critical reason for establishing and maintaining a disciplined approach to respirator selection.
Supplied Air Respirators (SAR) and Powered Air Purifying Respirators (PAPR) are the two most common classes of positive pressure respiratory protection employed in workplaces today. Determining which of these types is appropriate for a given situation requires understanding the job-specific variables, including the identity and concentration of contaminants that are present (or may be present) in the work area, as well as the work being performed in that area.
In evaluating the options that exist for respiratory protection, the safety director or industrial hygienist also must apply an understanding of the protective capabilities of the different types of respirators available within each of these classifications. Other factors, including worker health, worker comfort, cost, training, and preference, also should be taken into consideration. This article outlines a number of these issues as they relate to supplied air and powered air purifying respiratory protection.

Overview and General Considerations
SAR systems can be broken down into five basic components.
Air source: Typically, employers use a large compressor system as the air source for SARs, although other sources can be incorporated, such as Free-Air pumps or cascade systems of bottled air.
Filtration system/CO monitor: To maintain Grade D breathable air as required by OSHA, employers should use an in-line filtration system to filter the air coming from the compressor. When properly maintained, these systems prevent any contaminants from being transported through the compressor system and on to the worker. Carbon monoxide monitoring provides an essential safeguard to alert users and employers if an excessive amount of CO is being generated by the oil-lubricated compressor.
Distribution system: From the compressor, the air has to be transported to the work area where the workers can use it. Air distribution manifolds are a common way of aiding employers with this task. These manifolds (referred to as "points of attachment" in the regulations) consist of 1) a coupling that connects the respirator breathing air supply hose to the source of breathing air, 2) a pressure regulator, and 3) a pressure gauge. Often, these points of attachment will be an integral part of the filtration system and CO monitor. NIOSH and OSHA require that everything from the point of attachment to the worker be part of the approved respirator assembly and from the same manufacturer.
Air supply hose: The air supply hose connects to the point of attachment and transports breathable air to the worker. The air supply hose must be from the same manufacturer as the respirator being used, and it must be approved for use with the specific respirator being worn.
NIOSH-approved respirator: OSHA requires that employers use NIOSH-approved respirators in areas where respiratory protection is required. The NIOSH-approved respirator must be used in an approved configuration specified by the manufacturer. Any deviation from the approved configuration voids NIOSH approval.

PAPR systems can be broken down into four basic components.* PAPR blower unit: The blower unit is worn on the belt or attached to the respirator headpiece and draws air through filters and/or cartridges to provide air to the respirator headpiece.
Battery: The battery provides power to the blower unit. Batteries may be of different types and configurations. Many PAPRs use Nickel Cadmium (NiCad) batteries, while others use Nickel Metal Hydride (NiMh) batteries because of their light weight and longer working duration. Some PAPRs use an external battery that also attaches to the belt and is connected to the blower unit by a cord, while others have a more integrated design to eliminate the uneven weight distribution and snagging hazard associated with the former design.
Filters/cartridges: The filter(s)/cartridge(s) attach to the blower unit, filtering the air that is drawn through them by the blower unit's motor. Different filters and cartridges are available for different contaminants. Employers must identify and measure the contaminants before selecting the appropriate type. A change-out procedure for chemical cartridges must be established by the employer to help ensure continued respirator effectiveness.
Breathing tube and headpiece: The breathing tube transports the air from the blower unit to the headpiece, which is worn by the worker. Employers must select a headpiece appropriate for the contaminants and the level of protection needed on the job.
Selecting A Respirator
Most personal protective equipment manufacturers and distributors offer recommendations on choosing respirators. These recommendations may be available as an online or published guide or may even take the form of an on-site analysis of the workplace. Regardless of these recommendations, ultimately it is the responsibility of the employer to ensure the proper respirators are being used for worker protection and that they meet all local, state, and federal regulations.

The OSHA Web site,, offers a wealth of information that is useful in the selection process. One of the more recent additions to the site is the Respirator Selection eTool. This eTool steps you through the decision-making process of selecting a respirator, according to the NIOSH Respirator Decision Logic (RDL) and the OSHA standard for respiratory protection (29 CFR 1910.134).
Certain applications and/or situations will limit the types of respirators that may be used, and this is the first consideration that should be made when selecting a respirator. For example, in abrasive blasting, a Type CE respirator must be used not only to provide respiratory protection, but also to provide protection to the neck and torso from the rebound of the blast media. Another example involves respirators that are used in atmospheres deficient in oxygen content (less than 19.5 precent), contain concentrations of a contaminant that would be considered immediately dangerous to life or health, or have the potential for either of these to occur because of the nature of the work being performed. In all of these instances, workers would not be allowed to wear a PAPR but would be required to wear a self-contained breathing apparatus (SCBA) or pressure-demand supplied air respirator with auxiliary escape cylinder.
What Other Factors Should Be Considered?
Many distinguishing factors influence the appropriateness of an SAR or PAPR for a given work application. Each type of respirator has a distinct set of advantages and disadvantages that must be considered as they relate to workers' comfort, productivity, and protection. Below is an outline of some of the more prevalent tradeoffs found between SARs and PAPRs. The table below provides a more detailed view.
Worker mobility is a key concern in certain job functions. The ability, or inability, of a worker to move about can create both productivity and safety concerns. Worker mobility in a supplied air respirator is somewhat more restricted because of the limit on the length of the air supply hose. (As specified on the NIOSH approval label, air supply hoses are not to exceed 300 feet). The supply hose can present a "slip, trip, and fall hazard" to the worker wearing the respirator, as well as to those working in the same area. Worker mobility in a PAPR is not an issue, although it does bring about other issues such as the need for a cartridge change-out schedule.

Operating costs
There are various costs associated with both PAPRs and SARs. Operating costs for PAPRs include the cost of replacement cartridges, replacement headpieces, spare batteries, and other replacement parts. Recurring costs associated with SARs include replacement supply hose, replacement filter elements for any filtration system on the compressor system, replacement headpieces and other parts, and any operating costs associated with the compressor (electricity, maintenance, etc).

Administrative costs
Often overlooked are the administrative costs associated with having a particular type of respirator in use. While all respirators require the establishment of a written program that includes training (29 CFR 1910.134 (k)), there are other requirements specific to the type of respirator being used. Administrative duties related to PAPRs generally are greater, requiring the employer to establish and monitor a cartridge change-out schedule, as well as managing battery charging for multiple shift operations.

Comfort can be directly correlated with worker productivity and job satisfaction. Depending on the job requirements, the mobility offered by a PAPR system is the prime element of comfort. In some work environments, however, supplied air may offer an element of comfort that PAPRs cannot. Because SARs operate at high pressures, they are able to operate climate control (vortex) tubes to heat or cool the air entering the worker's respirator headpiece by as much as 30 degrees F. In work environments that are exceptionally hot or cold, vortex tubes can have a significant impact on worker comfort and productivity.

As is evident, safety directors and industrial hygienists must consider a number of different tradeoffs when determining the type of respiratory protection that is appropriate and suitable for a given job at a given workplace. By selecting and providing the best respirator for the job, the employer not only ensures that workers are properly protected, but also gives workers the opportunity to be more productive and happier during the work day.
This all adds up to lower liability and higher job satisfaction. It's well worth the effort to make an informed choice.


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