The current Ebola epidemic in West Africa is the largest in history and is unprecedented in many ways, including the large number of healthcare workers who have been infected while treating patients. The large scale of the epidemic, as well as the two healthcare workers who contracted Ebola while caring for the first case in the United States, has directed particular attention to the personal protective equipment (PPE) used by healthcare workers to reduce their risk of infection. PPE is designed to create a barrier to prevent pathogens from entering the body through the mucous membranes or broken skin. Examples of PPE used for Ebola include (but are not limited to) gloves, gown/coverall, mask/respirator, apron, faceshield/goggles, and cap/hood (see Figure 1). Reports from healthcare workers in West Africa indicate that some personnel are able to wear their PPE for only 40 minutes at a time because of the high ambient temperature and humid conditions. Even in the United States, where management of patients with Ebola is done in air-conditioned environments, uncomfortable PPE is a common complaint and causes additional burden for healthcare workers.
On September 26, 2014, in a speech at the Global Health Security Agenda Summit, President Obama announced a “Grand Challenge” to design improved PPE for use by healthcare workers during treatment of Ebola patients.
“And today, I’m pleased to announce a new effort to help health workers respond to diseases like Ebola. As many of you know firsthand, the protective gear that health workers wear can get incredibly hot, especially in humid environments. So today, we’re issuing a challenge to inventors and entrepreneurs and businesses of the world to design better protective solutions for our health workers. If you design them, we will make them. We will pay for them. And our goal is to get them to the field in a matter of months to help the people working in West Africa right now. I’m confident we can do this.”
The National Institute for Occupational Safety and Health (NIOSH), along with other offices in the U.S. Centers for Disease Control and Prevention (CDC), is partnering with the U.S. Agency for International Development (USAID), the White House Office of Science and Technology Policy (OSTP), the U.S. Department of Defense (DOD), and other U.S. agencies on the Fighting Ebola: A Grand Challenge for Development (Grand Challenge) to help healthcare workers on the front lines provide better care and stop the spread of Ebola. The USAID-led Grand Challenge consists of several initiatives, including developing, testing, and scaling entirely new PPE or modifications to current PPE that address issues of protection, heat stress, and comfort for healthcare workers. Key components of the Grand Challenge include broadly soliciting new ideas through social media (crowdsourcing), forging public/private partnerships, and providing critical funding for promising designs.
How NIOSH is Supporting the Grand Challenge and PPE Needs for the Ebola Response
For the past five months, NIOSH has evaluated the PPE ensembles currently used in West Africa and around the world (see Figure 1) for Ebola and collaborated nationally and internationally on efforts to develop solutions to improve PPE configurations in the future. NIOSH prioritized internal efforts to help inform healthcare workers and infection control and safety professionals about PPE best practices and selection options, including managing heat stress, identifying strategies for selecting protective clothing, and identifying NIOSH-approved powered-air purifying respirators consistent with CDC recommendations for use in managing patients with Ebola.
NIOSH is working closely with USAID, OSTP, and other federal partners on the Grand Challenge, including (but not limited to) participating in crowdsourcing events to promote innovation, reviewing promising ideas that can be scaled to the field, and setting performance, test, and evaluation requirements. NIOSH conducts research that supports the epidemic response and the Grand Challenge. A previous NIOSH science blog identified eight knowledge generation priorities for protecting workers from Ebola. Examples of current efforts include the following:
- NIOSH is using its sweating thermal manikin and conducting tests involving human subjects to evaluate several common PPE ensembles used in West Africa and around the world (see Figure 1) to better understand factors associated with heat stress and design features that affect comfort and job performance. The evaluation findings will be used to refine PPE recommendations. Data on the impact of wearing specific combinations of PPE are nonexistent (for example, how does putting an apron on top of a surgical gown affect heat stress?). Preliminary findings (unpublished) support anecdotal reports from healthcare workers in West Africa that certain PPE combinations will be difficult to wear for longer than 40 minutes in high heat and humidity conditions. These evaluations are critical because they set the baseline for the Grand Challenge. PPE manufacturers are constantly improving barrier materials and NIOSH plans to test innovative PPE prototypes as well as cooling systems proposed in response to the Grand Challenge as part of this evaluation effort. Overall, data from these tests are expected to help inform PPE selection options that allow healthcare workers to wear PPE for longer periods of time without undue stress or burden.
- NIOSH is performing research on isolation gowns (a common component of some PPE ensembles used in the Ebola epidemic) to evaluate their durability and ability to prevent penetration of viruses in blood and body fluids through the material. The findings of this project will be used in the development of a new standard specification for isolation gowns. This study builds upon NIOSH’s previous experience working with standards development organizations to establish PPE standards for prehospital workers (for example, emergency medical services workers and other medical first responders). The study will also help set the baseline for the Grand Challenge by providing performance data (e.g., tensile strength, tear strength, seam strength, water resistance, viral penetration, air permeability, etc.).
- NIOSH is undertaking studies to better understand key factors affecting penetration of microorganisms in blood and body fluids through protective clothing, such as the surface tension of the carrier liquid and microorganism size and shape. In one set of experiments, the “elbow lean test” is used to quickly evaluate different types of aprons, gowns, and coveralls under simulated use conditions with varying liquids of different surface tensions. In other experiments, NIOSH researchers use a modified version of the ASTM F1671 test method to study penetration of surrogate viruses of different sizes and shapes. These experiments will be used to advance protective clothing standards, validate or improve upon existing test methods, and inform the PPE selection process for protection against infectious pathogens like Ebola that spread via contact with blood and body fluids.
What Is Currently Known about Balancing Protection and Comfort?
Many workplace settings (construction, agriculture, wildland firefighting, hazardous materials response, manufacturing) require employees to wear PPE for extended periods of time in hot, humid, and extremely challenging environments. PPE reduces the ability of the wearer to cool off by limiting heat transfer from the body through sweat evaporation, convection, and radiation. PPE also adds to the amount of weight carried, further increasing heat load. However, the challenges faced in selecting PPE for the current Ebola epidemic in West Africa are unique. The selection of work-rest cycles to mitigate heat stress are constrained by the lack of single-use PPE, the extreme patient load (more and/or longer rest breaks are not practical), and limited staff to treat critically ill patients with Ebola.
Selecting PPE requires balancing protection and comfort/heat stress. This is not a new issue, nor is it unique to the Ebola epidemic. In general, discomfort increases with increased protection. To provide protection, PPE designers often must make certain sacrifices; sometimes, these include material choices (for example, using materials that are known to block blood and body fluids containing infectious materials from breaking through) that make the PPE less breathable and, thus, less comfortable for the wearer because it increases heat stress. Reducing protection is usually not a viable option, so the focus is on managing heat stress. The industrial hygiene community has decades of experience in developing strategies (for example, work-rest cycles) to manage heat stress, including “clothing adjustment factors” to account for the extra burden of the PPE
Another important aspect of the protection versus comfort trade-off is addressing the question, “What PPE constitutes an ’acceptable’ level of protection against pathogens like Ebola virus in blood and body fluids?” Fortunately, requirements and methods to evaluate the performance of PPE have been written by organizations that develop voluntary consensus standards. The most common standard in the United States for classifying healthcare protective apparel, including surgical and isolation gowns, is ANSI/AAMI:PB70 (2012). This standard defines four levels of liquid barrier performance, with Level 1 being the lowest level of protection and Level 4 being the highest level of protection. In addition to the highest level of liquid barrier performance, AAMI Level 4 gowns are tested for penetration of viruses using the ASTM F1671 test method. Barrier materials passing this test are considered impervious to viruses under normal use conditions. In other words, only PPE passing this test or similar tests done in Europe (ISO 16604) have been demonstrated to block viruses in simulated blood and body fluids from passing at a certain level of pressure (for example, to simulate leaning on a contaminated object) through the materials. See The National Personal Protective Technology Laboratory (NPPTL) website for a more detailed summary of the key protective clothing standards and test methods used in healthcare to assess protection against microorganisms in blood and body fluids.
To highlight the challenges in balancing comfort and protection, we created a table that summarizes what is currently known about the types of PPE commonly used in the Ebola epidemic. PPE are listed in order of expected levels of protection against pathogens in blood and body fluids, starting with the least protective PPE with the least amount of body coverage. For detailed PPE selection guidance for Ebola patient management, see CDC, the Occupational Safety and Health Administration, and the World Health Organization.
NIOSH hopes that the information in this blog will continue the dialogue on solutions to permit healthcare workers to wear their PPE safely and with less stress and burden for longer periods of time during patient care.
Ronald Shaffer, PhD
Dr. Shaffer is Chief of Technology Research Branch at NIOSH’s National Personal Protective Technology Laboratory.
For more information about Ebola, heat stress, or the NIOSH personal protective technology (PPT) program, visit the following websites:
White House Presentation: Innovation on the Edge: Accelerating Solutions in the Fight against Ebola (The discussion on personal protective equipment (PPE) starts at the 1 hour and 53 minute mark. The NIOSH update on PPE standards and testing is at the 2 hour and 26 minute mark.)
Table 1. PPE Options to Reduce Exposure to Blood and Body Fluid Pathogens: Balancing Protection vs. Comfort
|PPE Type||Relevant Standard||Protection Against Blood & Body Fluids/Viral Penetration||Discomfort2|
|Typical Barrier Properties1||Typical Body Coverage|
|Isolation/Surgical Gown||Unrated||Nonprotective||Limited to front torso, upper legs, and arms. Protection in back varies; some designs have open backs.||Low|
|AAMI – Level 1||Minimal ability to block fluids, sprays, and splashes. Does not pass viral penetration test.||Limited to front torso, upper legs, and arms. May have noncontinuous coverage in back.||Low|
|AAMI – Level 2||Low to moderate ability to block fluids, sprays, and splashes. Does not pass viral penetration test.||Limited to front torso, upper legs, and arms. May have noncontinuous coverage in back.||Low|
|AAMI – Level 3||Moderate ability to block fluids, sprays, and splashes. Does not pass viral penetration test.||Limited to front torso, upper legs, and arms. May have noncontinuous coverage in back.||Low|
|Lightweight, Single Use Coveralls3||n/a||Variable, depends upon manufacturer. Most are fluid resistant, but do not pass viral penetration test.||Full-body coverage except feet, hands, and face.||Low – Medium|
|Isolation/Surgical Gown||AAMI – Level 4||High ability to block fluids, sprays, and splashes. Passes viral penetration test.||Limited to front torso, upper legs, and arms. May have noncontinuous coverage in back.||Low|
|Chemical Protective Apron||n/a||Fluid/chemical resistant and generally pass viral penetration tests.||Limited to front torso and upper legs.||Medium|
|Limited use Chemical Protective Coverall3||n/a||Fluid/chemical resistant and generally pass viral penetration tests.||Full-body coverage except feet, hands, and face.||Medium – High|
- Details of which standards specific products have been tested against are often found in the PPE user instructions or available on the PPE manufacturer’s website.
- Based upon measured and estimated clothing adjustment factors in units of wet bulb globe temperature, with low defined as <2° C, medium ranging from 2-4° C, and high being greater >4° C. Clothing adjustment factors based upon data from the literature for aprons and coveralls and expert opinion of NIOSH researchers for gowns. Ranges reflect differences among manufacturers and across the different models within that type and may not include all of the PPE worn by healthcare workers during an Ebola epidemic.
- Includes microporous or selectively permeable membranes such as multi-/single-layer nonwoven fabrics.