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Air-Purifying Escape Hood Respirators (Escape Hoods): Interim Findings


April 2004

The National Institute for Occupational Safety and Health (NIOSH) has responsibility for testing and certifying respirators used to protect workers against occupational exposures to harmful air contaminants. NIOSH certification provides users with assurance that a certified respirator will provide expected protection.

In partnership with employer and employee representatives, respirator manufacturers, and other government agencies, NIOSH developed criteria for testing and certifying air-purifying escape hood respirators, commonly known as escape hoods, for emergency use in escaping chemical, biological, radiological, and nuclear (CBRN) exposures in the workplace. NIOSH finalized criteria in October of 2003 began accepting air purifying escape respirators for approval on November 6, 2003 and began accepting self-contained escape respirators for approval on January 2, 2004. Respirator certifications should be completed for some models over the coming months so that approved products will become available sometime later in the year. The NIOSH respirator page lists all approved CBRN respirators that finish the approval process.

Because of concerns about terrorism threats, a number of government employers purchased first generation escape respirators that pre-date the NIOSH CBRN escape respirator certification criteria. In the course of establishing certification criteria, NIOSH conducted exploratory tests to better understand the performance offered by existing escape hoods against a wide range of exposures. Those exploratory tests were used by NIOSH to develop practical, effective criteria for certifying escape hoods.

Although the military previously had tested escape hoods, these military criteria and tests differed from the NIOSH exploratory tests in that:

  • Military tests were not performed with the range of potential CBRN agents used in the NIOSH tests, and
  • NIOSH tests considered the physical characteristics of the U.S. working population, which is more diverse than the military population.

This fact sheet summarizes observations from NIOSH exploratory tests and provides interim guidance on training and use, based on those observations. The purpose of the fact sheet is to provide useful information for employers who are using first generation escape respirators. It highlights some limitations and provides guidance to address these limitations. The guidance on training and use is also relevant for NIOSH certified CBRN escape respirators. As CBRN certified escape respirator models become available, stakeholders will have a basis for assessing specific products and brands. As storage lifetimes expire over the next few years on first-generation models, employers will have the option to replace these models with NIOSH certified CBRN models. In the meantime, the summary information in this fact sheet offers interim guidance on training and use for employers, employees, and others to consider when implementing a program for escape hood respirators.

Design of the Exploratory Tests

NIOSH selected three commercially available models of escape hoods for exploratory testing. These models appear to represent the state-of-the-science in escape hood technology. The following types of tests were conducted:

  • The escape hoods were exposed to the chemical warfare agents Sarin (a nerve agent) and mustard (a blister agent), as well as to 11 representative Toxic Industrial Chemical (TIC) test agents which represent 139 TICs. The 139 TICs represented by these 11 test agents include chemical gases and vapors, and biological, radiological / nuclear, and chemical particulates. This was done to determine whether hazardous concentrations of those test materials penetrated the escape hoods. No human subjects were used in those tests.
  • In separate tests, the escape hoods were donned and used by seven human test subjects (four men and three women) at three levels of activity for ten minutes per activity: standing at rest, walking on a treadmill at 2.5 miles per hour, and walking on a treadmill at 3.5 miles per hour. These tests simulated donning and the levels of physical activity in which users might be engaged while wearing escape hoods. These tests did not involve exposure to Sarin, mustard, or toxic industrial chemicals. The tests examined:
    • The use of escape hoods, including components such as neck-seals and nose-cups, and the ability to use mouth-bits that are that are important to the performance of escape hoods.
    • The degree of ease or difficulty experienced in donning and using the escape hoods.
    • Levels of oxygen and carbon dioxide inside the escape hoods. Exhaling creates carbon dioxide; it is important that carbon dioxide levels do not rise too high and oxygen levels do not fall too low in the air that a person breathes.

Results of the Exploratory Tests

NIOSH’s test results indicated that:

  • The escape hood respirators provided adequate levels of protection against the chemical warfare agents Sarin and mustard. In general, the respirators provided adequate protection against 9 of the 11 representative TIC test agents: dioctyl phthalate, cyanogen chloride, cyclohexane, formaldehyde, hydrogen cyanide, hydrogen sulfide, phosgene, phosphine, and sulfur dioxide and inadequate levels of protection against 2 representative TIC test agents: ammonia and nitrogen dioxide. Based on experience from filter testing as part of the CBRN standards development program, those findings provide NIOSH with confidence that modifications are possible within current technology to protect against all the representative TIC agents used in the exploratory tests, and that such improvements will be incorporated in the next generation of escape hoods once the NIOSH testing and certification program is under way. The exploratory test findings do NOT provide a basis for determining whether all current escape hoods will have the same performance, or for offering guidance on choosing among different products currently on the market. The forthcoming NIOSH testing and certification program will provide a basis for such assessments.
  • In the tests involving human subjects, six of the seven persons were able to complete all three tests with at least one escape hood model with no difficulties. No user was able to don and wear every escape hood model for the duration of all three tests without some difficulties. Difficulties reported and observed during the tests among at least one person were hyperventilation, a statement that the user “could not breathe,” headache, lightheadedness, insufficient strength to pull the escape hood’s neck-seal over the user’s head, discomfort due to the tightness of the neck seal, and choking sensations. Some of these difficulties can be addressed through training on how to choose a properly fitting escape hood, and NIOSH expects that other difficulties will be solved with design innovations in the next generation of devices that meet the criteria of the NIOSH CBRN escape hood certification standard.
  • In some instances, levels of carbon dioxide inside the escape hood exceeded the NIOSH recommended limit of 2.5 percent in the air breathed for this type of respirator, and oxygen levels fell below the NIOSH recommended limit of at least 19.5 percent. Low levels of oxygen may impair muscle or movement coordination and increase fatigue. High levels of carbon dioxide may impair performance, produce headaches or dizziness, or reduce physical work capacity. Users may also experience psychological discomfort, potentially resulting in the urge to remove the hood. Although NIOSH did not observe high levels of carbon dioxide or low levels of oxygen that would pose serious risks for the general workforce, the levels observed in some cases would be of concern for vulnerable populations such as the elderly, or people with asthma or other respiratory impairments. NIOSH believes that these problems will be solved with the next generation of escape hoods.
  • Certain features made various escape hoods difficult to use for at least one person. The features include the following:
    • Neck-Seal. All three escape hoods tested had neck-seals made of a stretchable material that seals the hood around the neck. A neck-seal that is too tight may cause a user to experience difficulty in breathing or experience a sensation of strangulation. Some of the subjects found the neck-seal too tight in some of the escape hoods.
    • Nose-Cup. Two of the three escape hoods contained a nose-cup. A good nose-cup-to-face seal is required for reducing both carbon dioxide levels and fogging. One user reported an inability achieve a good nose-cup-to-face seal.
    • Mouth-bit and nose-clip. One of the escape hoods used a mouth-bit and nose-clip. The mouth-bit is used both to breathe purified air and expel breath. One user experienced a gag reflex relating to the use of the mouth-bit and was not able to wear that model of escape hood.
    • Non-adjustable head-harness. All three escape hoods had some type of harness on the inside or outside of the hood. In one case the harness was not adjustable. One user of the escape hood that had a non-adjustable head-harness reported that the harness was inadequate, allowing the nose-cup to slide around the face.

Interim Recommendations for Training and Use

Based on the results of the tests, NIOSH recommends that if escape hoods are to be used in a workplace, that employers establish and follow a program for how to choose escape hoods, how they are to be properly worn, and how employees are to be trained in their use. NIOSH offers the following interim guidance for respirator program managers, for incorporation as appropriate into their programs for assessing the characteristics of escape hood respirators and training employees in their use. These recommendations address the concerns most likely to be relevant to users pending availability of respirators that comply with NIOSH’s CBRN escape respirator certification standard and the accompanying development of formal users’ guidance. Note that OSHA has also created a Safety and Health Information Bulletin titled: “CBRN Escape Respirators” that provides guidance on use, selection, and training (SHIB 08-29-03).

Selection of Escape Respirators

Because the worker population is physically diverse and the design features of different models of escape hoods vary, employers should be aware that one particular model may not be appropriate for all individuals at a particular worksite. To address these issues, NIOSH recommends that employers consider the following aspects an effective escape hood respirator workplace plan:

  • As part of a training program for escape hoods, users should have the opportunity to try on a training model to see if it can be properly worn.
  • The employer should address the question of fit by assessing the unique characteristics of the particular work site. Possible approaches could include offering multiple sizes of the same model, similar model designs from the same or different manufacturers, or different model designs (for example, a model with a nose-cup and a model with a mouth-bit) from the same or different manufacturers.
  • If the employer has already purchased escape hoods, each employee should be assessed for his or her ability to wear the available model or models. If the model or models cannot be worn properly, the supplier or manufacturer may be able to offer guidance on what other options are available.
  • If the employer has not yet purchased escape hoods, it may be possible for the supplier or manufacturer to visit the work site to provide assistance on options.
  • NIOSH is not aware of any available information that would make it possible to offer more detailed guidance on accommodating escape hoods to the diverse workforce population. It is likely that collaboration between employer and employee groups, escape hood manufacturers, and government agencies would be needed to develop such guidance.
  • If a particular escape hood is available only in a “one-size-fits-all” model, it is important to ensure that the model will perform satisfactorily on users with unusual facial features, facial hair, or very small or very large necks.

Training in Use of Escape Respirators

Users should be given training on how to properly put on and use escape hood respirators, including information on the unique features of a particular model (each model has characteristics that are different from those of other models, and these unique features are important to the escape hood’s effectiveness). For example:

  • If the escape hood uses an inner nose-cup, it is important that the nose-cup seal properly to the face.
  • If the escape hood uses a mouth-bit and nose clip, it is important to be certain the individual can use those features without experiencing a gagging reflex.
  • If the escape hood has a tight neck-seal and the individual needs a certain degree of arm strength to stretch the neck-seal over his / her head, it is important to determine if the user possesses that degree of strength.
  • If the escape hood has a harness that cannot be adjusted to acquire a proper nose-cup-to-face seal, a different respirator model should be chosen that has a harness (either adjustable or non-adjustable) that aids in positioning the nose-cup to obtain a good seal. Escape hood head-harnesses should be used in accordance with the manufacturer’s instructions.
  • The manufacturer’s instructions on training in the use of escape respirators should always be followed. If a question is not addressed in the manufacturer’s manual or other product instructions, the manufacturer should be contacted for specific guidance related to the question.

Donning Escape Respirators

Users should always don (put on) escape hood respirators in accordance with the manufacturer’s instructions in order for the respirator to operate properly. If available, training respirators should be used to practice both donning and wearing, to assure maximum protection. Buying extra escape hood respirators for training should be considered if extra escape hoods are not already available; an escape hood is intended only for single use, and should never be used more than once. Individuals should periodically review the manufacturer’s training videos, written instructions, donning diagrams, and other available training materials. If a question is not addressed in the manufacturer’s manual or other product instructions, the manufacturer should be contacted for specific guidance related to the question.

Storing and Maintaining Escape Respirators

The manufacturer’s instructions on storing and maintaining escape respirators should always be followed. If a question is not addressed in the manufacturer’s manual or other product instructions, the manufacturer should be contacted for specific guidance related to the question.

Addressing Difficulties in Using Escape Respirators

Some users may have difficulty wearing an escape hood, for example, those who are pregnant, elderly, or who have pre-existing respiratory or cardiovascular conditions. These individuals should be pre-identified as part of the overall workplace emergency response and preparedness plan. Alternative arrangements for emergency escape should be planned for these individuals which reflect the fact that they may have more physical difficulty in an emergency situation than co-workers without similar conditions. For example, the employer might consider a “buddy system” in which co-workers agree to assist those individuals in an evacuation. The NIOSH certification standard for CBRN air-purifying escape respirators includes standardized caution and limitation statements which can be found as Attachment F to the criteria.

Further NIOSH information on respirators can be found on the Resporator Topic page. Once NIOSH completes certification of individual escape hood respirator models, notices of certification will be posted at the same site. NIOSH also plans to publish the results of its exploratory tests in a future technical publication.