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• Standard Number: 1910.146; 1910.146(c)(4); 1910.146(c)(9); 1910.146(d); 1910.146(d)(5)



May 12, 2009

Mr. Edwin C. Porter, Jr., CIH
Defense Contract Management Agency (DCMA)
Suite 300
6350 Walker Lane
Alexandria, VA 22310-3226

Dear Mr. Porter:

Thank you for your January 17, 2008, letter to the Occupational Safety and Health Administration's (OSHA's) Directorate of Enforcement Program's Office of General Industry Enforcement (GIE), regarding OSHA's permit-required confined spaces (PRCS) standard, 29 CFR 1910.146. Your scenarios and questions are restated below for clarity.

Scenario 1: The employer has identified a tail section of a helicopter, commonly referred to as a "tail boom" as a confined space under OSHA's PRCS standard. The space has one entry/exit port hole and is large enough for two or three workers at a time to occupy it and perform work. When a previously flown helicopter arrives for maintenance work, the space on that helicopter may have accumulated aviation fuel and exhaust gases, e.g., carbon monoxide, kerosene (JP-8). Also, 10/10 oil (petroleum distillates) rust inhibitor that has been sprayed all over the aircraft produces vapors that are trapped in the identified space.

Question 1: When the entry/exit port hole is opened prior to worker entry, what type of air monitoring must be conducted, and, at a minimum, what specific toxic chemicals must be air monitored?

Response: The standard requires air monitoring according to the atmospheric or potential atmospheric hazards within the permit space [29 CFR 1910.146(d)(5)(ii) (monitor "as necessary")]. Since the standard requires in paragraph (d) that the employer must identify and evaluate each hazard to which the entering employees will be exposed, the permit space would have to be monitored for the chemicals mentioned in your scenario.

Question 2: If workers must occupy several areas within this confined space, must all of those various areas be air monitored prior to worker entry?

Response: Yes, since the standard requires monitoring "as necessary" of any areas that may contain potential or actual atmospheric hazards, prior to the workers entering those areas [29 CFR 1910.146(d)(5)(ii)].

Question 3: How many air monitoring samples are necessary to determine that this confined space is safe to enter?

Response: The standard requires that conditions in the permit space must be tested to determine if acceptable entry conditions exist before entry is authorized to begin [29 CFR 1910.146(d)(5)(i)]. Also, certain atmospheric hazards may not be uniformly distributed within the confined space; please see Appendix B, Procedures for Atmospheric Testing in 29 CFR 1910.146. The space's size and configuration may require continuous monitoring and varied sampling locations during entry work in those areas [29 CFR 1910.146(d)(5)(i)].

Question 4: Can the air monitoring be performed with both direct-reading instruments and non-direct-reading air sampling methods?

Response: The employer must ensure that conditions in the permit space are acceptable prior to entry and throughout the duration of entry operations [29 CFR 1910.146(d)(5)(ii)]. This is accomplished through the use of test instruments to monitor the atmosphere within the permit space. As described in your scenario, direct-reading test instrumentation may provide adequate air monitoring, as long as all atmospheric hazards are detectable using this method.

Question 5: Can workers wear non-direct-reading air monitoring devices, e.g., charcoal tubes attached to low flow pumps and passive badge dosimeters when the employer is first assessing the space to determine if it is a permit-required confined space?

Response: If direct-reading instrumentation does not exist for the contaminant to be monitored, then non-direct-reading air monitoring devices are an employer's only alternative. When first assessing a confined space using such sampling equipment, testing should be conducted without entry to reduce employee exposures. If, however, employees must enter a space for an initial assessment, and there are unknown concentrations of atmospheric hazards, then employees must wear approved airline respirators or a self-contained breathing apparatus (SCBA).

Scenario 2: This scenario presents the same helicopter tail boom as described in scenario 1. All of the jet fuel exhaust gases have dissipated or have been ventilated out of this confined space. The 10/10 oil (petroleum distillates) have evaporated, dissipated, or have been ventilated out as well. The airborne levels of these toxics have been documented below their respective PELs by air monitoring data. At this point, no toxics remain in this confined space. However, work must now be done inside this tail boom confined space with adhesives and paint primer that contain toluene and hexavalent chromium (Cr (VI)), respectively.

Question 1: Is there a certain quantity of adhesive or paint-containing toluene and hexavalent chromium that is safe for workers to use within this confined space?

Response: Based on the information provided, OSHA is unable to determine a quantity of material that would trigger a hazardous or potential hazardous atmosphere in this space, other than OSHA's PELs for specific air contaminants. The employer has the duty to make that determination given the quantity of material used and the manner in which it is applied.

Question 2: Does OSHA require air monitoring to determine the concentration level of toluene?

Response: OSHA would require air monitoring to determine whether toluene has the potential to create or is creating an atmospheric hazard. Acceptable entry conditions must exist and be verified throughout the duration of an authorized entry [29 CFR 1910.146(d)(5)].

Question 3: Since toluene has acute health hazards associated with it, is this confined space automatically considered to be a permit-required confined space, until proven otherwise, and is air monitoring data required to prove that this confined space is not a permit-required confined space?

Response: It would depend on factors such as, but not limited to, the quantity of material used in the space, the size and configuration of the space, and temperature.

Question 4: Since hexavalent chromium is a carcinogen, is this confined space automatically considered to be a permit-required confined space, until proven otherwise, and is air monitoring data required to prove that this confined space is not a permit-required confined space?

Response: The use of hexavalent chromium within the space would not automatically trigger the permit space classification, unless it presents an acute health hazard, as some carcinogens, such as Cr (VI) do. Hexavalent chromium has a recommended immediately dangerous to life and health (IDLH) limit published by the National Institute of Occupational Safety and Health (NIOSH) of 15 [milligrams] per cubic meter of air1. Therefore, employers must perform air monitoring in this scenario to document this is not a PRCS. In addition, employers introducing or producing air contaminants such as Cr (VI) inside a confined space (or in any other workplace) must also determine airborne exposures to ensure that PELs are not exceeded and to ensure appropriate controls are used in accordance with OSHA's substance-specific standards, such as 29 CFR 1910.1026 for Cr (VI).

Question 5: Must a direct-reading instrument be used to monitor the toxic air contaminants within this confined space?

Response: The employer must ensure that conditions in the permit space are acceptable prior to entry and throughout the duration of entry operations [29 CFR 1910.146(d)(5)]. Please see our response to the previous Question 5.

Question 6: Can the air monitoring be performed with both direct-reading and non-direct-reading instruments when classifying the space as a confined space or permit-required confined space?

Response: Given this scenario, if the employer does not know what atmosphere exists in this confined space, the employer must treat the confined space as a permit space. Please see the responses to Question 4 and 5, in the first scenario given above.

Question 7: Can the curing times of this toluene-based adhesive and primer be used, rather than air monitoring to determine the concentration level of toluene?

Response: The standard requires air monitoring or testing [29 CFR 1910.146(d)(5)]. The employer can use curing times in addition to air monitoring to help inform entrants of atmospheric hazards.

Question 8: Is air monitoring the only acceptable method for evaluating if the toluene concentration level is safe for entry into this space?

Response: OSHA is unaware of another method available to determine if the atmosphere is safe for entry. See 29 CFR 1910.146(d)(5).

Question 9: To initially determine whether the space is a permit space, can workers wear non-direct-reading air monitoring equipment, like charcoal tubes connected to low-flow pumps or passive dosimeters, while they apply this adhesive and primer inside this confined space?

Response: The initial entry would have to be made under the permit space entry operations with all of the PRCS requirements, including, but not limited to, air monitoring. When, as in this scenario, toxic materials are going to be used during entry, the employer must follow the complete permit space program in order to assure that all measures necessary for the protection of entrants are followed. The employer's evaluation of the space before entry must take into account these additional sources of hazardous atmospheres that will be introduced into the space during entry. Pre-entry monitoring alone would be insufficient.

Scenario 3: The fuel tank wings of a B-2 Bomber meet the OSHA definition of a "confined space." It has one entry/exit port hole, and the space is large enough for several workers at a time to occupy the space and perform work. When a previously flown B-2 Bomber arrives for maintenance work, its wing fuel tanks are drained and depuddled of JP-8 jet fuel (primary constituent is Kerosene). However, in this particular aircraft, the JP-8 jet fuel gets absorbed into the composite wing material because this aircraft, unlike most aircraft, does not have rubber bladders inside its wings. Therefore, even though the fuel tanks are drained and depuddled, there still would be JP-8 jet fuel off-gassing from the composite wing tank material when workers enter this confined space to perform work.

Question 1: When the entry/exit port hole is opened up and before a worker enters this confined space, what type of air monitoring must be conducted, and, at a minimum, what specific toxic chemicals must be air monitored?

Response: The type of air monitoring would depend on the type of atmospheric or potential atmospheric hazards within the permit space. If the substances you have listed in your scenario, or any others, would pose such hazards, then the permit space would have to be monitored for those chemicals. In addition, 29 CFR 1910.146(d)(5)(iii) requires that the permit space must first be tested for oxygen, then for combustible gases and vapors, and then for toxic gases and vapors.

Question 2: If workers must occupy several areas within this confined space, must all of those various areas be air monitored prior to worker entry?

Response: Yes, any areas that may contain potential or actual atmospheric hazards must be monitored prior to the workers entering those areas [29 CFR 1910.146(d)(5)(i)].

Question 3: How many air monitoring samples are necessary to determine that this confined space is safe to enter?

Response: See response to Question 3 in the first scenario.

Question 4: Can the air monitoring be performed with both direct-reading and non-direct-reading instruments, or is one type preferred over another, or is one type only allowed in certain situations, and what would those situations be?

Response: Please see our response to Questions 4 and 5 in the first scenario.

Question 5: Can workers wear non-direct-reading air monitoring equipment, for example charcoal tubes connected to low-flow pumps or passive dosimeters, while applying this adhesive and primer inside this confined space to assess this confined space when the employer is first determining if the confined space is a permit-required confined space?

Response: Please see our response to Questions 4 and 5 in the first scenario.

In addition you requested further clarification on a previous OSHA Letter of Interpretation to the U.S. Army Corps of Engineers, dated June 1, 1995. Answer 2.B. responds, "If the exhaust gases of the vehicle used to drive to the inspection site present an acute hazard (not chronic), then the space and hazard present meet the definition of a PRCS."

Question 1: Does this mean that simply having the presence of exhaust gases, e.g., carbon monoxide, at any concentration within this confined space makes this space a permit-required confined space? Or was this answer supposed to include a particular concentration of exhaust gases, e.g., 25 ppm of carbon monoxide, to trigger this space becoming a permit-required confined space?

Response: If there is a potential for an actual or potential atmospheric hazard due to the exhaust, then the permit-space classification is triggered [29 CFR 1910.146(b)] (see the definition of permit-required confined space). No particular concentration is given, but the mere presence of a detectable amount of exhaust gas may not necessarily trigger the classification in all scenarios.

Question 2: Must this confined space be treated as a permit-required confined space prior to employee entry and during air monitoring to assess the toxic or hazardous atmosphere?

Response: Yes, until the employer determines that the confined space does not contain or have the potential to contain a hazardous atmosphere, the employer must treat the space as a permit-required confined space [29 CFR 1910.146(c)(4) and 1910.146(d)]. For additional information, see 58 Federal Register 4462, 4481.

Question 3: The scenario uses exhaust gases, but does this apply to all chemicals with an acute hazard, for instance toluene?

Response: Entry into a confined space, in order to determine if it is a permit-space, must be done under full permit-required confined space entry conditions [58 FR 4481]. This would apply to any chemical that has or has the potential to create an atmospheric hazard.

In addition, you requested further clarification on OSHA's Directive CPL 02-00-100 - CPL 2.100 - Application of the Permit-Required Confined Spaces (PRCS) Standards, 29 CFR 1910.146.

Question 1: In Appendix D, what does OSHA mean by the term "historical data" when used in this context with identifying permit spaces?

Response: Please be advised that Appendix D has been included for general guidance only. It is not intended to direct the Compliance Safety and Health Officer's investigation or restrict the manner in which an employer' program is evaluated. Within the PRCS standard, OSHA does not have a specific definition of "historical data." However, historical data may include, but is not limited to, sampling results, material safety data sheets, production records, etc.

Question 2: How much historical air monitoring data is sufficient to evaluate a confined space that contains a chemical like toluene?

Response: OSHA is unable to determine that amount given the information provided.

Question 3: Additionally, what does OSHA mean by the term "reliable" when used in this context with the term "historical data"?

Response: OSHA would look at the integrity of the historical data, how dependable, accurate, and appropriate it is.

Question 4: If an employer knew or suspected that acetone, toluene, and xylene was in the atmosphere of their confined space, would OSHA allow the employer to simply test the air for total volatile organic compounds (VOC) rather than each of these specifically?

Response: An employer would be required to test for potential atmospheric hazards using the appropriate instrumentation. In some situations, screening samples for multiple contaminants may be an appropriate initial test. However, the accuracy of testing and monitoring equipment may be significantly affected under certain conditions of humidity, pressure, or temperature, or by the presence of interfering chemicals. Adherence to the manufacturer's instructions for calibration and use is necessary in order to assure that levels for combustibility and toxicity have not been exceeded.

Question 5: If an employer had an employee bring an eye dropper full (2 milliliters) of toluene into a confined space, would OSHA allow the employer to use the gas laws (e.g., Boyle's law, Charles' law, Gay-Lussac's law) for equilibrium under static conditions, assuming uniform air mixing, to determine the maximum expected concentration within a confined space of known volume and complete evaporation of the toluene, to determine if this confined space is a permit-required confined space?

Response: An employer could look to applying the gas laws as part of its overall evaluation to determine if a space may contain a potential atmospheric hazard. However, OSHA cannot state that applying the gas laws in all circumstances, regardless of quantity, will identify a potential atmospheric hazard or not.

Question 6: If an employer had employees brush paint with a coating containing toluene inside of a confined space, would OSHA allow the employer to use the paint manufacturer's assigned cure time to determine whether the space was a confined space or a permit-required confined space?

Response: Appropriate monitoring would need to be conducted.

Question 7: Would the cure time need to be supplemented with air monitoring data for toluene to determine if the confined space was a permit-required confined space?

Response: See response to Question 6 above.

In addition, you requested information regarding the performance of various State Consultation Programs. We understand that you have received a response to these questions from OSHA's Directorate of Cooperative and State Programs.

Additionally, you stated that DCMA does not create or control any confined spaces or permit-required confined spaces. DCMA is a separate employer who performs inspection work in a contractor's/employer's permit-required confined spaces.

Question: Which paragraph of §1910.146 applies to DCMA?

Response: All of §1910.146 would apply to DCMA, if its employees are exposed to hazards of entry into permit-required confined spaces. See 29 CFR 1910.146(c)(9).

Thank you for your interest in occupational safety and health. We hope you find this information helpful. OSHA requirements are set by statute, standards, and regulations. Our interpretation letters explain the 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. In addition, 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 http://www.osha.gov. If you have any further questions, please feel free to contact the Office of General Industry Enforcement at (202) 693-1850.

Sincerely,



Richard E. Fairfax, Director
Directorate of Enforcement Programs



[1  NIOSH Pocket Guide to Chemical Hazards, DHHS (NIOSH) Publication No. 2005-149, September 2005]   [Return to Text]

[Corrected on November 1, 2010]


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