Research on respiratory requirements and powered air purifying respirator (PAPR) design is being conducted to improve the use of PAPRs and other respirators by health care workers. Four workshop speakers discussed the physiological needs of health care workers and how to improve PAPR mechanical function for the health care setting.
RESPIRATORY DEMANDS OF THE HEALTH CARE WORKFORCE
Philip Harber, University of Arizona
Focusing on the personal protective equipment (PPE) needs of health care workers involves examining the types of work they are performing and the real-world situations that they must deal with while in protective gear. Much of the research discussed in this presentation applies to all types of respirators and is not specific to PAPRs. Harber’s presentation focused on four key points:
- Human respiratory physiology is complex, and therefore, a single flow rate criterion is not the solution.
- Assessments of real-life utilization may be more important than the protection factor.
- Design features for PAPRs or other types of PPE can affect utilization and need to be measured and assessed in laboratory settings.
- Health care workers are diverse and have differing respiratory demands depending on their physiology and the types of work they are doing, in addition to other factors.
Respirator design must account for the respiratory burden to the user as well as the impact of the action of breathing on a respirator’s protection—that is, on the respirator’s effectiveness. To assess PAPR burden on the user, laboratory methods should be as noninvasive as possible in order to avoid interfering with normal breathing or with the operation of the PAPR. Measures of chest and abdominal movement can provide fairly accurate and direct measurements.
Breathing does not occur at a constant rate; inhalation and exhalation rates are not constant and can vary considerably. Thus, pressure and flow rates can vary widely depending on the level of physical exertion and other factors. Respirators should provide protection at the peak inspiratory flow rate. The pressure gradient is another key factor in physiological studies of the impact and effectiveness of respiratory protection.
The pathway to respiratory protection involves numerous steps including but not limited to identifying the agent, identifying persons at risk, choosing the proper respirator, training users, motivating users, making the respirator available, ensuring proper respirator function (e.g., battery is available and working), checking that the respirator is properly used, ensuring an adequate facial seal and filter effectiveness, and confirming proper equipment maintenance. Although some of the answers may not be available and quantifiable (e.g., filtration effectiveness), it is possible to “set up reasonable ranges and then look at which factors have the bigger influence on the overall utility.”
Just as the engineering design is tested in the certification process, it is possible to conduct more testing on implementation issues, including donning and doffing times and effectiveness, training measures, and subjective and comfort issues. A decision support system could be effective.
EVALUATING PHYSIOLOGICAL REQUIREMENTS WHEN USING PAPRs
National Personal Protective Technology Laboratory
The National Personal Protective Technology Laboratory (NPPTL) is conducting research to characterize the physiological and subjective responses to PAPR use. This research examines work rates that are similar to those found in health care settings. It is ongoing work, so final results are not yet available. The three parts of the ongoing study are (1) to conduct physiological measurements of participants using a treadmill to
elicit specific work rates similar to those experienced by health care workers; (2) to survey the participants about their experience wearing the PAPR, especially with regard to noise level, comfort, and ease of communication; and (3) to use an automated breathing and metabolic simulator to assess the impact of varying work rates, breathing rates, and humidity levels.
NPPTL is testing several models of PAPRs—one with a tight-fitting hood and three with loose-fitting hoods. One of the areas of study has focused on understanding how carbon dioxide and oxygen levels change when PAPRs are worn at three different work rates.
Varying intensities of physical activity in health care work (and thus varying demands on airflow within the PAPR) could be examined for four work situations: (1) desk work, such as entering patient notes into a computer; (2) operating room procedures; (3) moving patients; and (4) emergency calls by paramedics or physical therapists performing patient care. The use of MET (metabolic equivalent of task) to classify PAPRs by energy expenditure could be helpful in respirator selection. The Compendium of Physical Activities uses METs and other measures to categorize the level of physical activity involved in work, and this approach could be considered as a way to overcome the subjectivity of terms for work such as “heavy” or “light,” which people perceive differently (Ainsworth et al., 2000).
PAPR Batteries and Performance
National Personal Protective Technology Laboratory
Batteries powering a respiratory protective device are what make a respirator a PAPR, and they can greatly improve worker ease of use and comfort. Batteries are specifically matched with PAPR components (blowers, hoods, helmets, filtering components, and chargers). The National Institute for Occupational Safety and Health (NIOSH) certifies the complete PAPR respirator assembly, including the battery. Currently there are no requirements for the batteries or their chargers to be interchangeable or interoperable. PAPRs generally use one of three types of rechargeable batteries—nickel cadmium, nickel metal hydride, or lithium ion—or a non-rechargeable disposable battery that could be alkaline, lithium sulfur dioxide, or lithium manganese oxide. PAPRs are tested for the robustness of their batteries with the silica dust test, which draws a silica
dust cloud through the PAPR for 4 hours. Battery management is an important part of the respiratory protection program for PAPRs. Whether in use or not, batteries are constantly discharging and do not maintain their charge indefinitely in storage. Lithium ion batteries have become a preferred battery choice because they have a small discharge rate in storage (approximately 5 to 10 percent per month) compared to nickel cadmium batteries and nickel metal hydride batteries (approximately 30 percent per month).
Batteries that have not been used for several months may require reconditioning—that is, discharging and recharging to restore capacity before use. Battery instructions need to be made more easily available, as they are not always provided with the blower assembly or with the charger instructions.
Because of their battery power, PAPRs have the capacity to offer a number of product features that would be helpful to users, including battery check lights, indicators of airflow rates or duration of use, and monitors for the end-of-service life on the canisters and cartridges.
Battery power could also allow for product features to be added that would increase the utility and performance of PAPRs in the health care setting, such as electronic microphones for easier communication. Furthermore, different types of PAPRs with different assigned protection factors could be considered if the demand was evident. “Once you define those technical specifications in the engineering world, we’ll link it to standards, and manufacturers will produce to those standards.” The health care community has the market share to drive the PAPR market in a way similar to how the firefighter community drove the requirements for self-contained breathing apparatuses and helped to set National Fire Protection Association standards. Efforts are under way, including Project BREATHE (discussed earlier by Lewis Radonovich), NIOSH evaluation initiatives, and field studies to identify the respiratory protection needs of health care workers and the tasks and capabilities that should be specified for future respirators that more closely meet the needs of the health care workforce.
IMPACT OF CERTIFICATION STANDARDS ON RESEARCH AND DESIGN
Larry Green, Syntech International
PAPRs could be designed to better meet the needs of different work environments, including health care. Regulations should be written so
that the tests are appropriate for the design features needed for a particular work environment. The obvious test that is currently required but that does not apply to the health care work environment is the silica dust test, which, as noted by other speakers, is designed for a mining or other dusty work environment. For health care, “combining LRPL [Laboratory Respirator Protection Level] testing with active airflow and battery-level warnings should be allowed in place of silica dust testing.” Consideration should also be given to loose-fitting PAPRs being tested as part of a PPE system that integrates with a surgical gown or other body covering.
Some of the lessons that can be learned from surgical helmet systems, which look similar to PAPRs but are not certified as respiratory protection, include
- Increase visibility by designing for a wide and clear visibility field with optically clear lenses;
- Improve communication by decreasing noise from the blower;
- Reduce weight of the PAPR to improve comfort;
- Reduce carbon dioxide levels to the fullest extent possible;
- Ensure that the battery meter and airflow alarm are easily visible;
- Avoid hyperthermia by ensuring a cooling airflow and minimize breathing resistance; and
- Integrate the hoods or cowls into protective clothing systems, particularly with consideration of how the donning and doffing of the PPE is done, to maintain sterile PPE on initial contact with a patient and lack of contact with contaminated equipment when removing the PPE.
Green concluded by suggesting, “the key to new advances are appropriate regulations which dictate sound design and applicable standards based on the widest range of needs, not a narrow set of tests applicable to a narrow set of needs.”
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