Personal Protective Equipment: Questions and Answers, CDC

Personal Protective Equipment: Questions and Answers

Updated March 14, 2020

This document is intended to address frequently asked questions about personal protective equipment (PPE).


  • CDC’s guidance for Considerations for Selecting Protective Clothing used in Healthcare for Protection against Microorganisms in Blood and Body Fluids outlines the scientific evidence and information on national and international standards, test methods, and specifications for fluid-resistant and impermeable gowns and coveralls used in healthcare.
  • Many organizations have published guidelines for the use of personal protective equipment (PPE) in medical settings. The American National Standards Institute (ANSI) and the Association of the Advancement of Medical Instrumentation (AAMI): ANSI/AAMI PB70:2012 pdf icon external icon describes the liquid barrier performance and a classification of surgical and isolation gowns for use in health care facilities.
  • As with any type of PPE, the key to proper selection and use of protective clothing is to understand the hazards and the risk of exposure. Some of the factors important to assessing the risk of exposure in health facilities include source, modes of transmission, pressures and types of contact, and duration and type of tasks to be performed by the user of the PPE. (Technical Information Report (TIR) 11 pdf icon external icon [AAMI 2005]).
  • For gowns, it is important to have sufficient overlap of the fabric so that it wraps around the body to cover the back (ensuring that if the wearer squats or sits down, the gown still protects the back area of the body).

Nonsterile, disposable patient isolation gowns, which are used for routine patient care in healthcare settings, are appropriate for use by patients with suspected or confirmed COVID-19.

  • While the transmissibility of COVID-19 is not fully understood, gowns are available that protect against microorganisms. The choice of gown should be made based on the level of risk of contamination. Certain areas of surgical and isolation gowns are defined as “critical zones” where direct contact with blood, body fluids, and/or other potentially infectious materials is most likely to occur. (ANSI/AAMI PB70 pdf icon external icon ).
  • If there is a medium to high risk of contamination and need for a large critical zone, isolation gowns that claim moderate to high barrier protection (ANSI/AAMI PB70 Level 3 or 4 pdf icon external icon ) can be used.
  • For healthcare activities with low, medium, or high risk of contamination, surgical gowns (ANSI/AAMI PB70 Levels 1-4 pdf icon external icon ), can be used. These gowns are intended to be worn by healthcare personnel during surgical procedures.
  • If the risk of bodily fluid exposure is low or minimal, gowns that claim minimal or low levels of barrier protection (ANSI/AAMI PB70 Level 1 or 2 pdf icon external icon ) can be used. These gowns should not be worn during surgical or invasive procedures, or for medium to high risk contamination patient care activities.
  • CDC’s guidance for Considerations for Selecting Protective Clothing used in Healthcare for Protection against Microorganisms in Blood and Body Fluids provides additional comparisons between gowns and coveralls.
  • Gowns are easier to put on and, in particular, to take off. They are generally more familiar to healthcare workers and hence more likely to be used and removed correctly. These factors also facilitate training in their correct use.
  • Coveralls typically provide 360-degree protection because they are designed to cover the whole body, including the back and lower legs, and sometimes the head and feet as well. Surgical/isolation gowns do not provide continuous whole-body protection (e.g., they have possible openings in the back, and typically provide coverage to the mid-calf only).
  • The level of heat stress generated due to the added layer of clothing is also expected to be less for gowns when compared to coveralls due to several factors, such as the openings in the design of gowns and total area covered by the fabric.
  • Check to see if your facility has guidance on how to don and doff PPE. The procedure to don and doff should be tailored to the specific type of PPE that you have available at your facility.
  • If your facility does not have specific guidance, the CDC has recommended sequences for donning and doffing of PPE. pdf icon
  • It is important for Health Care Providers (HCP) to perform hand hygiene before and after removing PPE. Hand hygiene should be performed by using alcohol-based hand sanitizer that contains 60-95% alcohol or washing hands with soap and water for at least 20 seconds. If hands are visibly soiled, soap and water should be used before returning to alcohol-based hand sanitizer.

Unlike patient care in the controlled environment of a healthcare facility, care and transport by EMS present unique challenges because of the nature of the setting. Coveralls are an acceptable alternative to gowns when caring for and transporting suspect COVID-19 patients. While no clinical studies have been done to compare gowns and coveralls, both have been used effectively by healthcare workers in clinical settings during patient care. CDC’s Considerations for Selecting Protective Clothing used in Healthcare for Protection against Microorganisms in Blood and Body Fluids guidance provides a comparison between gowns and coveralls, including test methods and performance requirements. Coveralls typically provide 360-degree protection because they are designed to cover the whole body, including the back and lower legs, and sometimes the head and feet as well. This added coverage may be necessary for some work tasks involved in medical transport. However, coveralls may lead to increased heat stress compared to gowns due to the total area covered by the fabric. Training on how to properly remove (doff) a coverall is important to prevent self-contamination. Comparatively, gowns are easier to put on and, in particular, to take off.


Nonsterile disposable patient examination gloves, which are used for routine patient care in healthcare settings, are appropriate for the care of patients with suspected or confirmed COVID-19.

  • The American Society for Testing and Materials (ASTM) external icon has developed standards for patient examination gloves.
  • Standard specifications for nitrile gloves, natural rubber gloves, and polychloroprene gloves indicate higher minimum tensile strength and elongation requirements compared to vinyl gloves. 1,2,3,4
  • The ASTM has developed standards for patient examination gloves. Length requirements for patient exam gloves must be a minimum of 220mm-230mm depending on glove size and material type. 1,2,3,4

CDC Guidance does not recommend double gloves when providing care to suspected or confirmed 2019-COVID patients.

According to CDC Guidance, extended length gloves are not necessary when providing care to suspected or confirmed COVID-19 patients. Extended length gloves can be used, but CDC is not specifically recommending them at this time.

  • Check to see if your facility has guidance on how to don and doff PPE. The procedure to don and doff should be tailored to the specific type of PPE that you have available at your facility.
  • If your facility does not have specific guidance, the CDC has recommended sequences for donning and doffing of PPE pdf icon .
  • It is important for HCP to perform hand hygiene after removing PPE. Hand hygiene should be performed by using an alcohol-based hand sanitizer that contains 60-95% alcohol or washing hands with soap and water for at least 20 seconds. If hands are visibly soiled, soap and water should be used before returning to alcohol-based hand sanitizer.


1 ASTM D6319-Standard Specification for Nitrile Examination Gloves for Medical Applications

2 ASTM D3578 Standard Specification for Rubber Examination Gloves

3 ASTM D5250 Standard Specification for Poly(vinyl chloride) Gloves for Medical Application

4 ASTMD 6977 Standard Specification for Polychloroprene Examination Gloves for Medical Application


Most often, spread of respiratory viruses from person-to-person happens among close contacts (within 6 feet). Recent studies indicate that people who are infected but do not have symptoms likely also play a role in the spread of COVID-19. CDC recommends everyday preventive actions to prevent the spread of respiratory viruses, such as avoiding people who are sick, avoiding touching your eyes or nose, and covering your cough or sneeze with a tissue. People who are sick should stay home and not go into crowded public places or visit people in hospitals. Workers who are sick should follow CDC guidelines and stay home when they are sick.

A respirator is a personal protective device that is worn on the face or head and covers at least the nose and mouth. A respirator is used to reduce the wearer’s risk of inhaling hazardous airborne particles (including infectious agents), gases or vapors. Respirators, including those intended for use in healthcare settings, are certified by the CDC/NIOSH.

An N95 FFR is a type of respirator which removes particles from the air that are breathed through it. These respirators filter out at least 95% of very small (0.3 micron) particles. N95 FFRs are capable of filtering out all types of particles, including bacteria and viruses.

  • Infographic: Understanding the difference between surgical masks and N95 respirators pdf icon
  • N95 respirators reduce the wearer’s exposure to airborne particles, from small particle aerosols to large droplets. N95 respirators are tight-fitting respirators that filter out at least 95% of particles in the air, including large and small particles.
  • Not everyone is able to wear a respirator due to medical conditions that may be made worse when breathing through a respirator. Before using a respirator or getting fit-tested, workers must have a medical evaluation to make sure that they are able to wear a respirator safely.
  • Achieving an adequate seal to the face is essential. United States regulations require that workers undergo an annual fit test and conduct a user seal check each time the respirator is used. Workers must pass a fit test to confirm a proper seal before using a respirator in the workplace.
  • When properly fitted and worn, minimal leakage occurs around edges of the respirator when the user inhales. This means almost all of the air is directed through the filter media.
  • Unlike NIOSH-approved N95s, facemasks are loose-fitting and provide only barrier protection against droplets, including large respiratory particles. No fit testing or seal check is necessary with facemasks. Most facemasks do not effectively filter small particles from the air and do not prevent leakage around the edge of the mask when the user inhales.
  • The role of facemasks is for patient source control, to prevent contamination of the surrounding area when a person coughs or sneezes. Patients with confirmed or suspected COVID-19 should wear a facemask until they are isolated in a hospital or at home. The patient does not need to wear a facemask while isolated.
  • A surgical N95 (also referred as a medical respirator) is recommended only for use by healthcare personnel (HCP) who need protection from both airborne and fluid hazards (e.g., splashes, sprays). These respirators are not used or needed outside of healthcare settings. In times of shortage, only HCP who are working in a sterile field or who may be exposed to high velocity splashes, sprays, or splatters of blood or body fluids should wear these respirators, such as in operative or procedural settings. Most HCP caring for confirmed or suspected COVID-19 patients should not need to use surgical N95 respirators and can use standard N95 respirators.
  • If a surgical N95 is not available for use in operative or procedural settings, then an unvalved N95 respirator may be used with a faceshield to help block high velocity streams of blood and body fluids.

The requirements for surgical N95 respirators that make them resistant to high velocity streams of body fluids and help protect the sterile field can result in a design that has a higher breathing resistance (makes it more difficult to breath) than a typical N95 respirator. Also, surgical N95 respirators are designed without exhalation valves which are sometimes perceived as warmer inside the mask than typical N95 respirators. If you are receiving complaints, you may consider having employees who are not doing surgery, not working in a sterile field, or not potentially exposed to high velocity streams of body fluids wear a standard N95 with an exhalation valve.

An N95 respirator with an exhalation valve does provide the same level of protection to the wearer as one that does not have a valve. The presence of an exhalation valve reduces exhalation resistance, which makes it easier to breathe (exhale). Some users feel that a respirator with an exhalation valve keeps the face cooler and reduces moisture build up inside the facepiece. However, respirators with exhalation valves should not be used in situations where a sterile field must be maintained (e.g., during an invasive procedure in an operating or procedure room) because the exhalation valve allows unfiltered exhaled air to escape into the sterile field.

The NIOSH approval number and approval label are key to identifying NIOSH-approved respirators. The NIOSH approval label can be found on or within the packaging of the respirator or sometimes on the respirator itself. The required labeling of NIOSH-Approved N95 filtering facepiece respirators pdf icon includes the NIOSH name, the approval number, filter designations, lot number, and model number to be printed on the respirator. You can verify that your respirator approvals are valid by checking the NIOSH Certified Equipment List (CEL).

When NIOSH becomes aware of counterfeit respirators or those misrepresenting NIOSH approval on the market, these respirators are posted on the Counterfeit Respirators / Misrepresentation of NIOSH-Approval webpage to alert users, purchasers, and manufacturers.

NIOSH does not require approved N95 filtering facepiece respirators (FFRs) be marked with an expiration date. If an FFR does not have an assigned expiration date, you should refer to the user instructions or seek guidance from the specific manufacturer on whether time and storage conditions (such as temperature or humidity) are expected to have an effect on the respirator’s performance and if the respirators are nearing the end of their shelf life.

In times of increased demand and decreased supply, consideration can be made to use N95 respirators past their intended shelf life. However, the potential exists that the respirator will not perform to the requirements for which it was certified. Over time, components such as the strap and nose bridge may degrade, which can affect the quality of the fit and seal. Prior to use of N95 respirators, the HCP should inspect the respirator and perform a seal check. Additionally, expired respirators may potentially no longer meet the certification requirements set by NIOSH. For further guidance, visit Release of Stockpiled N95 Filtering Facepiece Respirators Beyond the Manufacturer-Designated Shelf Life: Considerations for the COVID-19 Response.

Monitoring PPE supply inventory and maintaining control over PPE supplies may help prevent unintentional product losses that may occur due to theft, damage, or accidental loss. Inventory systems should be employed to track daily usage and identify areas of higher than expected use. This information can be used to implement additional conservation strategies tailored to specific patient care areas such as hospital units or outpatient facilities. Inventory tracking within a health system may also assist in confirming PPE deliveries and optimizing distribution of PPE supplies to specific facilities.

Know Nuclear

Know Nuclear Science Protecting Against Exposure

Protecting Against Exposure

Time, Distance and Shielding
There are three general guidelines for controlling exposure to ionizing radiation:

  • minimizing exposure time,
  • maximizing distance from the radiation source,
  • shielding yourself from the radiation source.

Time is an important factor in limiting exposure to the public and to radiological emergency responders. The amount of radiation exposure increases and decreases with the time people spend near the source of radiation. The maximum time to be spent in the radiation environment is defined as the “stay time.” The stay time can be calculated using the following equation:

Stay Time = Exposure Limit/Dose Rate

Distance can be used to reduce exposure. The farther away people are from a radiation source, the less their exposure. Doubling the distance from a point source of radiation decreases the exposure rate to 1/4 the original exposure rate. Halving the distance increases the exposure by a factor of four.

How close to a source of radiation can you be without getting a high exposure? It depends on the energy of the radiation and the size (or activity) of the source. Distance is a prime concern when dealing with gamma rays, because they can travel at the speed of light. Alpha particles can only travel a few inches and beta particles around 10 feet.

Shielding: As ionizing radiation passes through matter, the intensity of the radiation is diminished. Shielding is the placement of an “absorber” between you and the radiation source. An absorber is a material that reduces radiation from the radiation source to you. Alpha, beta, or gamma radiation can all be stopped by different thicknesses of absorbers.

Shielding material can include barrels, boards, vehicles, buildings, gravel, water, lead or whatever else is immediately available.

α ALPHA – can be stopped after traveling through about 1.2 inches of air, about 0.008 inches of water, or a piece of paper or skin. A thin piece of paper, or even the dead cells in the outer layer of human skin, provides adequate shielding because alpha particles can’t penetrate it. However, living tissue inside the body offers no protection against inhaled or ingested alpha emitters.

β BETA – can only be stopped after traveling through about 10 feet of air, less than 2 inches of water, or a thin layer of glass or metal. Additional covering, for example heavy clothing, is necessary to protect against beta-emitters. Some beta particles can penetrate and burn the skin.

γ GAMMA: To reduce typical gamma rays by a factor of a billion, thicknesses of shield need to be about 13.8 feet of water, about 6.6 feet of concrete, or about 1.3 feet of lead. Thick, dense shielding is necessary to protect against gamma rays. The higher the energy of the gamma ray, the thicker the shield must be. X-rays pose a similar challenge. This is why x-ray technicians often give patients receiving medical or dental X-rays a lead apron to cover other parts of their body.

Are Vapor Barriers Required or Recommended?

During the energy crisis of the 1970s, a prevailing belief took root where it was thought that tightly sealing walls and ceilings with a vapor barrier was essential to blocking heat transference and reducing energy costs. It was soon determined, however, that unless the seal was absolute, moisture that did get into sealed walls could create serious structural problems and health issues, such as allergic reactions to mold festering within walls. Although it is still good practice to minimize heat loss through walls, ceilings, and floors, it is now known that it is equally important for the vapor barriers to be installed correctly and that walls also are able to «breathe.»

Resolution of the Vapor Barrier Debate

Some debate still occurs over how necessary vapor barriers are, but a consensus is growing closer. Most authorities now agree that vapor barriers are important under certain conditions, but not necessarily as a whole-house solution for every home. In circumstances where conditions inside a home or office are much different than outdoor conditions, water vapor is likely to move through wall cavities and can get trapped inside, and a well-installed vapor barrier is recommended. Vapor barriers can also be important for certain rooms where moisture levels are especially high.

The Science of Moisture Movement

Water vapor can pass through building materials in several ways, including direct transmission, and by heat transfer, but studies suggest that fully 98 percent of the moisture transfer through walls occurs through air gaps, including cracks around electrical fixtures and outlets, and gaps along baseboards. Thus, installing vapor barriers on wall surfaces must be done in conjunction with sealing these air flow-gaps in walls and ceilings, and along floor surfaces.

Note that a poor effort at establishing a vapor barrier may be worse than no effort at all. The goal of vapor barrier strategies is to prevent moisture from collecting and corrupting building materials. Improperly installed, a vapor barrier may actually trap moisture inside a wall, while a wall that is more porous can breathe effectively and be less susceptible to long-term moisture problems. This condition is especially problematic where vapor barriers are installed on inside as well as outside wall surfaces, as such a wall cannot breathe at all

Do I Need a Vapor Barrier?

Once thought to be essential throughout a home or office, vapor barriers are now strongly recommended only for certain conditions, and methods for creating a vapor barrier must be tailored to fit the climate, region, and type of wall construction. For example, the recommended vapor barrier in a home or office in a humid southern climate built with brick varies greatly from creating a vapor barrier in a cold climate in a home built with wood siding. Always refer to current local code recommendations when deciding if and how to install vapor barriers. Avoid adding interior vapor barriers where the outer wall construction already includes a material with vapor barrier properties.

Most authorities recommend vapor barriers in certain situations:

  • In areas with high humidity—such as greenhouses, rooms with spas or swimming pools, and bathrooms—vapor barriers are often recommended. Consult building inspection offices for local recommendations.
  • In very cold climates, the use of polyethylene plastic vapor barriers between insulation and interior wallboard may be beneficial, provided all air gaps into any wall and ceiling cavities are also blocked. The exterior face of the wall or floor cavity should remain permeable in order to allow dissipation of any moisture that does enter the wall cavity.
  • Very hot and humid climates may benefit from an exterior vapor barrier that keeps outside humidity from penetrating into walls.
  • Below-grade walls and floor slabs transmit ground moisture through concrete walls or slabs. A vapor barrier against the concrete surface is generally recommended before wood framing or flooring materials are installed.
  • Crawl spaces benefit from a polyethylene moisture barrier placed directly over the exposed earth.

Tips for Installing Vapor Barriers

If vapor barriers are warranted by local building practices and code recommendations, keep the following practices in mind:

  • Buildings should meet ASHRAE standards 62.2 or 62.1 for proper ventilation before being sealed by complete vapor barriers. Modern homes or offices that are tightly sealed in order to be highly energy efficient should also have air-to-air heat exchangers or other methods of ensuring a good exchange of fresh air
  • Don’t use impermeable vapor barriers where semi-permeable or permeable materials provide satisfactory performance. Construction methods that allow interior wall materials to dry out are considered better than those that seek to prevent all moisture from entering
  • Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions: the inner surface in colder climates and the outer surface in hot, humid climates.
  • In existing spaces, oil-based paints or vapor-barrier latex paints offer an effective moisture barrier.
  • Avoid fully impermeable barriers, such as polyethylene or vinyl wall coverings, on spaces that are air-conditioned. This practice has been linked to moldy buildings and other air quality problems.
  • Avoid installing vapor barriers on both sides of a structure. Walls and ceiling cavities should ideally have the ability to dry out in one direction if the other side is constructed to prevent moisture penetration.
  • Seal all wall cracks and holes in the wall being vapor-proofed to block air gaps. Use special sealing tape to join sheets if polyethylene sheets are being used. Complete air blockage is essential to provide a satisfactory moisture barrier, and will also maximize the wall’s energy efficiency.
  • Use acoustic spray-foam sealant or sealant tape to block spaces around electrical boxes at outlets, switches, or ceiling light fixtures.

Vapor Transmission Ratings

To assist builders in controlling moisture, various building materials are rated according to permeability and are assigned a perms rating. A variety of rating systems are in use, but one common one is the U.S. permeability system.

Impermeable materials are those rated at less than 1 U.S. perms. Some examples include:

  • Glass
  • Sheet metal
  • Polyethylene sheet
  • Rubber membrane
  • Vapor-retardant paints
  • Exterior-grade plywood
  • Foil-faced rigid insulation board

Semi-permeable materials are rated at 1 to 10 U.S. perms. Some examples include:

  • Unfaced expanded or extruded polystyrene
  • 30-pound asphalt-coated paper (tar paper)
  • Interior-grade plywood
  • Bitumen-coated kraft paper
  • Foil- or paper-faced batt insulation
  • Gypsum board painted with oil-based or moisture-retardant latex paint

Permeable materials are rated at 10 U.S. perms or above. Some examples include:

  • Unpainted gypsum board (drywall)
  • Fiberglass insulation (unfaced)
  • Cellulose insulation
  • Board lumber
  • Concrete block
  • Concrete slabs
  • Brick
  • 15-pound asphalt-coated paper (tar paper)
  • House wrap

Impermeable materials are not always desirable, as in some situations a wall needs permeable materials in order to properly breathe and rid itself of excess moisture. Most experts advise against sealing a wall on both sides, as this is a prescription for trapping moisture and fostering the inherent problems it creates.

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