Constructing a Powered Air Purifying Respirator System

When properly selected, used and maintained, powered air purifying respirator systems (PAPRs) can provide increased comfort, protection and regulatory flexibility for workers exposed to hazardous atmospheres.

As an air purifying respirator, a PAPR relies on filters and cartridges just like the more familiar negative pressure air purifying respirators. It also has similar safe use conditions (e.g., contaminant identity and concentration must be known, respirator does not supply oxygen).

What makes the PAPR different from the negative pressure respirators is the inclusion of a motor blower, which pulls the air through the filter and blows it into the wearer's breathing zone. This can produce a number of advantages over negative pressure respirators, depending on the application and workplace conditions.

ADVANTAGES

Improved Comfort

Because the motor blower pulls the air through the filter, breathing resistance virtually is eliminated. This can help reduce the wearers' overall workload. In addition, depending on the air temperature, the mechanical movement of air over the wearer's head and face may provide a feeling of cooling in hot or strenuous work environments. (It should be noted that, unlike some supplied air systems, PAPRs do not have the capacity to directly cool or heat the air.)

Regulatory Flexibility

PAPRs offer significant flexibility in regards to regulatory requirements. In the United States, OSHA respirator regulations (29 CFR 1910.134) prohibit facial hair from coming between the respirator sealing surface and the wearer's face. These regulations also require the wearer of a tight-fitting facepiece be fit tested annually. PAPRs can be equipped with loose-fitting hoods or headcovers, which accommodate limited facial hair — provided the facial hair does not come between the headgear seal and face. Loose-fitting hoods and head covers also allow the user to waive the fit-testing requirement.

PAPRs using tight-fitting facepieces, however, still require fit testing. The fit test must be done with the facepiece in the negative pressure mode. The wearer can remove the facepiece from the PAPR and use various manufacturer supplied parts to convert the facepiece to a negative pressure version. An alternate method is to don the fully assembled PAPR but conduct the fit-test with the motor blower off. This will automatically put the facepiece into a negative pressure configuration.

Higher APF

PAPRs can offer higher assigned protection factors (APF) for an air purifying system. A PAPR used with a tight-fitting facepiece has an OSHA designated APF of 1,000 — significantly higher than the APF of 10 for a half facepiece or 50 for a full face- piece negative pressure respirator. Also, the full face is granted a 50 APF only if a quantitative fit test (e.g., using a Portacount or similar device) is conducted. Without a quantitative fit test, the full face negative pressure respirator has an APF of 10. Conversely, a tight fitting PAPR can use the less expensive qualitative fit test (e.g. Bitrex solution) to achieve the 1,000 APF.

PAPRs utilizing loose-fitting head covers (headgear that provides a partial seal with the face, typically around the chin) have an APF of 25 — still significantly higher than a half facepiece or a full facepiece respirator when qualitatively fit tested. PAPRs with full hoods (headgear that includes a shroud that covers the neck and reaches to the shoulders) have a minimum APF of 25. Most manufacturers, however, can supply the proper test documentation to allow an APF of 1000 to be assigned to the system using a full hood.

Medical Flexibility

Finally, because the PAPR reduces the respirator breathing resistance, it may be an option for a worker who has been medically disqualified from wearing a negative pressure respirator. A potential PAPR wearer still must undergo a medical evaluation to determine if he or she can safely wear the proposed respirator.

INITIAL DETERMINATION

Before deciding which specific PAPR to use, several requirements need to be assessed.

1. Contaminants — Like all air purifying respirators, the contaminants and their concentration must be known. Most PAPRs have both particulate and gas/vapor filtration capability. Some PAPRs, however, are specialized for particulates only, so it is critical to identify exactly what contaminants will need to be filtered.

   Contaminant concentration also must be within the capacity of the respirator - less than both of the following limits:

   • The immediately dangerous to life or health concentration (IDLH) and

   • The maximum use concentration — the product of the APF times the Occupational Exposure Limit (OEL).

   Finally, oxygen levels must be greater than 19.5 percent.

2. Hazardous Locations — PAPR motors are electrically powered by a battery pack worn by the wearer. If the work site contains or could contain a potentially flammable/explosive atmosphere, a PAPR that meets appropriate intrinsic safety and hazardous location protection concepts may be required. PAPR manufacturers' literature should state the classes, divisions and temperature groups to which the PAPR has been tested.

3. Work Area Size — In general, the PAPR motor blower is worn on a belt around the waist. The size of the work area therefore must be taken into account. Narrow or restricted spaces must be evaluated to ensure the PAPR wearer can move safely around the work area.

4. Head gear — Prior to selecting a PAPR, the user needs to decide what features the headgear must have, such as a tight-fitting full facepiece, a loose-fitting hood, chemical splash protection or if the head gear needs to provide ANSI Z87.1 face protection or ANSI Z89.1 head protection.

   Once these factors are evaluated, a specific respirator system can be determined and specific component selection can begin.

CONSTRUCTING A PAPR

Many PAPR manufacturers have multiple components that can be mixed to design a system customized to the wearer's specific needs. The NIOSH PAPR approval label and manufacturers' catalogs and technical service should be consulted to identify which components can be used with the PAPR system and in what combination. Component selection consists of:

1. Motor blower — This is the heart of the system and will determine what other features are available (e.g. hazardous location entry, filter combinations, head gear).

2. Head gear — Select the head gear to be used based on the needed APF and other considerations noted above (e.g., facial hair, head protection, chemical protection).

3. Breathing tube — The breathing tube connects the head gear to the motor blower and conveys the filtered air to the wearer. Some manufacturers have a selection of tubes such as different lengths and materials to accommodate workers of different heights or aggressiveness of the work environment.

4. Filter cartridge — The cartridge must be appropriate to the contaminants to be encountered.

5. Battery pack — Manufacturers may have a selection of battery packs. The battery pack typically provides a nominal 4- to 8-hour run time. A shorter run time allows a lighter battery pack, but may need to be changed out during an 8-hour shift. Eight-hour packs are heavier but may not require change out. Rechargeable battery packs must continuously be maintained according to the manufacturer's recommendations to ensure maximum service life duration.

Selecting a PAPR requires a careful examination of the worksite and task requirements. By choosing the right PAPR, employers can maximize the advantages offered by these protective devices.

Donald J. Garvey, CIH, CSP, is technical service specialist for 3M Co. He has over 25 years experience in occupational safety and health and is currently the product specialist for powered air and emergency response respirators for 3M. Prior to 3M, Garvey was a construction industrial hygienist for 16 years, and is past chair of the American Industrial Hygiene Association Construction Committee.