OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.


May 1, 2008

The Honorable John E. Sununu
United States Senate
Washington, DC 20510

Dear Senator Sununu:

Thank you for your letter of January 9, 2008 on behalf of Mr. William Costello, Vice President of the FirePASS Corporation ("FirePASS"), concerning his company's request for a permanent variance for its fire-prevention technology. You asked that the Occupational Safety and Health Administration ("OSHA") provide the scientific rationale it applied in denying FirePASS's variance request and to respond to the questions that Mr. Costello included as an attachment in his letter to you.

Over the last year, OSHA has responded to similar questions raised by Mr. Costello, first in a letter addressing enforcement of the relevant provisions of OSHA's Respiratory Protection Standard and then in a letter denying FirePASS's proposed variance. It should be noted that Mr. Costello has not provided OSHA with any engineering drawings or other detailed documentation describing FirePASS's system. Enclosed with this letter are copies of previous correspondence with Mr. Costello, as well as Senator Patty Murray. Also enclosed are some relevant technical documents. In addition to this correspondence, a number of OSHA employees have had extensive telephone conversations and e-mail exchanges with Mr. Costello about these issues.

This letter first provides a general discussion of the requirements specified in OSHA's Respiratory Protection Standard related to oxygen-deficient atmospheres. It then responds to the specific questions submitted by you and Mr. Costello.

Oxygen-deficient atmosphere requirements in the Respiratory Protection Standard

Oxygen comprises 20.9 percent of the atmosphere. The OSHA Respiratory Protection Standard ("the Standard"; 29 CFR 1910.134) uses 19.5 percent oxygen as the level below which an oxygen-deficient atmosphere exists and requires, generally, that all oxygen-deficient atmospheres be considered immediately dangerous to life or health ("oxygen-deficient IDLH"). In the preamble to the final Standard, OSHA provided the following explanation for considering workplace atmospheres containing less than 19.5 percent oxygen as oxygen-deficient IDLH:


Human beings . . . begin to suffer adverse health effects when the oxygen level of their breathing air drops below [19.5 percent oxygen] . . . . At concentrations of 16 to 19.5 percent, workers engaged in any form of exertion can rapidly become symptomatic as their tissues fail to obtain the oxygen necessary to function properly . . . . Increased breathing rates, accelerated heartbeat, and impaired thinking or coordination occur more quickly in an oxygen-deficient environment. Even a momentary loss of coordination may be devastating to a worker if it occurs while the worker is performing a potentially dangerous activity, such as climbing a ladder. Concentrations of 12 to 16 percent oxygen cause tachypnea (increased breathing rates), tachycardia (accelerated heartbeat), and impaired attention, thinking, and coordination . . . , even in people who are resting.

At oxygen levels of 10 to 14 percent, faulty judgment, intermittent respiration, and exhaustion can be expected even with minimal exertion . . . . Breathing air containing 6 to 10 percent oxygen results in nausea, vomiting, lethargic movements, and perhaps unconsciousness. Breathing air containing less than 6 percent oxygen produces convulsions, then apnea (cessation of breathing), followed by cardiac standstill. These symptoms occur immediately. Even if a worker survives the [oxygen deficiency], organs may show evidence of [oxygen-deficiency] damage, which may be irreversible . . . . (63 FR 1159.)



Therefore, to prevent these serious health effects from occurring when employees are exposed to oxygen-deficient atmospheres, the Standard requires employers to provide employees with either a self-contained breathing apparatus (SCBA) or a combination full-facepiece pressure-demand supplied-air respirator (SAR) with an auxiliary self-contained air supply.


Question (1): What is the scientific rationale OSHA applied in denying FirePASS's proposed variance?

Reply (1): While OSHA has serious scientific and technological concerns about the FirePASS system as discussed later in this letter, it based its denial of FirePASS's proposed variance on the legal requirements for permanent variances set forth in the Occupational Safety and Health Act of 1970 ("OSH Act"; 29 USC 651, 655) and the level of protection provided to employees by FirePASS's system. Section 6(d) of the OSH Act requires that a proposed variance "provide employment and places of employment to . . . employees which are as safe and healthful as those which would prevail if [the employer] complied with the standard." Section 6(d) recognizes that employers may wish to develop alternative means of complying with a standard, but also ensures that employees do not suffer adverse health effects as a result.

In its variance application, FirePASS proposed to expose employees to an oxygen-deficient atmosphere without providing them with the respirators required by the Standard. Under the OSH Act, FirePASS must set forth a means of compliance that provides the same level of safety as the Standard. FirePASS's variance application refers to an attached document for a description of its proposed alternative measures. Paragraph 1.5 ("Proposed guidelines for entering FirePASS environment") describes the proposed alternative measures as follows:



  • You will be enetering (sic) the same environment (sic) as being in an airplane, if you have issues being in an airplane, please take the proper precautions.
  • Anyone with a clean bill of health under the age of 40 should have no problems.
  • People between the ages of 40 and 65 should check their oxyhemoglobin (SPO2) levels by a pulse oximeter before entering the environment (sic) and should have a reading of 95% or above.
  • Employees in the ages 40-65 should wear a pulse oximeter for the first week to monitor the SPO2.
  • Employees must evacuate the environment if their SPO2 levels drop below 87%.
  • Employees who suffer from respiratory diseases, such as emphysema or severe asthma, should not enter this environment without getting their doctor's permission (sic) or should wear a supplemental oxygen mask provided by the employer.
  • If you feel shortness of breath or light headiness (sic) or any other unusual symptoms, you should step out of the environment immediately.

On its face, these alternative measures do not provide the level of protection required by Congress under the OSH Act. The Standard is designed to protect employees from the adverse health effects of oxygen-deficient atmospheres. FirePASS's alternative, rather than preventing these health effects from occurring, requires employees to take action after adverse health effects have already begun. Under the strict requirements for variances set forth in the OSH Act, OSHA cannot accept this alternative.

Question (2): How does OSHA measure oxygen availability for human respiration?

Reply (2): OSHA measures oxygen availability for human respiration using the percent of oxygen by volume in the workplace atmosphere. OSHA adopted this approach because it is the usual and customary practice among industrial-hygiene professionals to refer to oxygen-deficient atmospheres in terms of the percent of oxygen by volume. Also, in assessing oxygen levels in the workplace, employers often use hand-held meters that measure these levels, and the meters display this information as percent of oxygen by volume. By using terminology in the Standard that is consistent with these measurements, employers can determine immediately whether an atmosphere is safe for employee exposure. As a result, employers do not have to perform the additional step of calculating the oxygen partial pressure using a complex formula that, if not performed correctly, could have serious consequences for employees.

OSHA recognizes that partial pressure of oxygen is the metric that reflects oxygen availability to the respiratory system. OSHA used partial pressure metrics to determine when, in terms of percent oxygen and altitude, employees can safely escape from an oxygen-deficient atmosphere, should their SCBAs or SARs malfunction. In these situations, OSHA determined that employers may use SCBAs and SARs that supply employees with at least 19.5 percent oxygen by volume to protect their employees without the auxiliary self-contained air supply generally used for escape purposes (see 59 FR 58905 and 63 FR 1202). These requirements are set forth in paragraph 1910.134(d)(2)(iii) and Table II of the standard.

OSHA also recognizes that the partial pressure of oxygen decreases with increasing altitude under ambient air conditions. So long as the percent oxygen by volume remains at least 19.5, OSHA permits employees to work at altitudes (up to 14,000 feet) without respiratory protection even though the partial pressure of oxygen is less than it is at sea level. Comments submitted to the rulemaking record addressed this issue by stating that employees who work and live at altitude have adjusted physiologically to the reduced partial pressures of oxygen (see 63 FR 1203). Thus, when employees have acclimated to elevations where the ambient air contains normal oxygen levels, but the partial pressure of oxygen is less than it is at sea level, OSHA believes air-supplied respirators are unnecessary to ensure employee safety.

In raising this question, Mr. Costello stated that, by measuring oxygen availability in terms of oxygen percent by volume, the Standard would allow employees to work in ambient air at the summit of Mt. Everest. While ambient air at this altitude (over 29,000 feet) has 20.9 percent oxygen by volume, it has an extremely low partial pressure of oxygen (i.e., the oxygen available would be insufficient to keep the employee alive). However, contrary to Mr. Costello's assertion, footnote 1 of 1910.134 Table II requires employers to provide employees working at altitudes above 14,000 feet with respirators that supply them with oxygen-enriched breathing air, which has an oxygen content in excess of 20.9 percent by volume. This requirement ensures that adequate oxygen is available to employees at high altitudes to prevent the harmful effects of oxygen deficiency.

Question (3): Does the Standard provide employers with a false sense of security and put employees at risk? If not, why not?

Reply (3): The Standard does not provide employers with a false sense of security and put employees at risk. In asking this question, Mr. Costello is referring to the fact that, with increasing altitude, the percent of oxygen in the atmosphere remains constant, but the partial pressure of oxygen (expressed as millimeters of mercury or mm Hg) decreases, meaning that less oxygen is available physiologically for use by employees. Mr. Costello is questioning whether employers will assume that 19.5 percent oxygen at sea level is equivalent to 19.5 percent oxygen at high altitudes, thereby, giving them a false sense of security and putting their employees at risk for oxygen deficiency. Contrary to this assertion, employees who work and live at altitude have adjusted physiologically to these conditions, as noted above in our response to the second question.

OSHA believes that the requirements of the Standard, developed from a complete and extensive rulemaking record, provide employees with the most reliable respirator protection available. By complying with these requirements, employers can be assured that their employees will have sufficient oxygen to perform their jobs safely and effectively.

Question (4): Will OSHA provide a copy of the study it references in adopting the 19.5 oxygen concentration as the threshold for safety for oxygen availability in the Respirator Standard?

Reply (4): OSHA is enclosing with this letter copies of the exhibits referenced in the preamble to the Standard that it used in adopting 19.5 percent oxygen by volume as the safe threshold for oxygen availability. When it developed the Standard, OSHA established a docket (i.e., number H049), available to the public, that includes the studies and references used in preparing the Standard. Mr. Costello may access and print any document in this docket by going to OSHA's Web page at http://www.osha.gov, and selecting "Dockets & E-Mail Comments," then "Use the easy search page" under "Search Dockets," entering "H049" to the right of "Docket Number," and then "Search."

Question (5): Why did OSHA disregard the input from Dr. Weissman of NIOSH?

Reply (5): OSHA did not disregard the input from Dr. Weissman of NIOSH when it reviewed FirePASS's proposed variance. When OSHA reviewed the proposed variance, it carefully considered the information contained in the letter sent by Dr. Weissman to Mr. Costello on April 27, 2007. Dr. Weissman prepared his letter in response to Mr. Costello's request for information on medical and scientific considerations concerning work in low-oxygen settings and not the technology employed by FirePASS. In his letter, Dr. Weissman concluded:

Those at greatest risk [in an oxygen-deficient atmosphere] would be older employees and those with health conditions such as pulmonary disease, cardiovascular disease, or anemia. Also, employees with lung disease and exertional demands greater than the resting level might experience greater hypoxemia. In addition to potential adverse health effects, hypoxemia might also affect neuropsychiatric function, resulting in safety issues such as increased risk for injuries.



The information in Dr. Weissman's letter clearly shows that exposing certain employees to the oxygen-deficient atmospheres proposed by FirePASS could result in serious adverse health effects. Dr. Weissman's letter confirmed that the alternative means of compliance proposed by FirePASS in its variance request would not provide protection that is equivalent to the protection afforded to employees by the Standard.

Question (6): Why is OSHA requiring thousands of employees to wear supplemental oxygen devices when FirePASS's proposed variance would allow them to work in controlled environments having 15 percent oxygen?

Reply(6): As stated repeatedly in this letter, OSHA determined that the system will not provide protection to the thousands of employees who use respirators in oxygen-deficient atmospheres as required by the standard. Based on the extensive record evidence obtained during the rulemaking, OSHA concluded that the requirement to use SARs and SCBAs under oxygen-deficient work conditions protects all employees by preventing adverse health effects. As described above, FirePASS's system would cause certain employees to experience adverse health effects from oxygen deficiency.

Additionally, after reviewing FirePASS's system, OSHA has serious concerns regarding the health and performance effects on employees who cycle through oxygen-deficient atmospheres on a daily basis (e.g., eight hours of exposure to an atmosphere containing 15 percent oxygen, followed by 16 hours of exposure to air at 20.9 oxygen) over the years of employment. Acclimation to oxygen-deficient environments takes approximately four weeks. Therefore, employees cycling between the FirePASS-generated atmosphere and ambient atmosphere will not have an opportunity to acclimate to the oxygen-deficient conditions. OSHA believes that failure to acclimate to these conditions could have serious consequences for employees with existing medical conditions affecting the lungs, heart, kidneys, and central nervous system.

Under the Standard, FirePASS could use its system in a workplace and not provide respirators to employees, if, for example, the system raised the oxygen level in a protected area to at least 19.5 percent prior to employees entering the area. This alternative would be practical, and still preserve the fire-retardant properties of the oxygen-deficient atmosphere for areas that house documents or equipment that only require infrequent access by employees. Additionally, it would be safe and healthful for all employees.

Thank you for your concern regarding this important issue.


Edwin G. Foulke, Jr.