The NIOSH, National Personal Protective Technology Laboratory (NPPTL), is currently reevaluating its limitations on and precaution for safe use of positive-pressure closed-circuit self-contained breathing apparatus. As stated in the Federal Register (Vol. 50, No. 222, pages 47456 – 47457 dated Monday, November 18, 1985) NIOSH’s position on this topic is:

Available information does not demonstrate, to the satisfaction of NIOSH, that positive-pressure closed-circuit self-contained breathing apparatus which use a breathing gas of pure oxygen can be used during direct exposure to open flames and/or high radiant heat and assure the wearer’s safety. Therefore, NIOSH has determined that until it has been demonstrated to the satisfaction of NIOSH that those devices can be worn under such conditions, it is prudent to presently limit the use of positive-pressure closed-circuit self-contained breathing apparatus which use pure oxygen breathing gas to mines and mining atmospheres which do not involve exposure to open flames or high radiant heat.

Background

NIOSH/NPPTL is currently developing performance concepts as part of the rulemaking process to develop a Closed-Circuit Self-Contained Breathing Apparatus (CC-SCBA) Module. This process has identified the need for flame and heat durability requirements to be considered as part of the module. One possible inclusion to the requirements is the National Fire Protection Agency (NFPA) Heat and Flame Test, NFPA 1981, Section 8.11. NIOSH has conducted laboratory testing on two manufacturer’s apparatus. The initial testing followed NFPA testing procedures with the exception of using a “dummy” cylinder in lieu of the oxygen cylinder. Test results were encouraging and presented at NIOSH/NPPTL public meetings held on July 19, 2005 and on October 12, 2006. The same tests will be conducted with full oxygen cylinders during 2008.

Additional research was garnered through testing conducted at a second laboratory where NPPTL personnel witnessed a Flame Engulfment Test.  Department 8 of the Association for the Promotion of German Fire Safety has included the same requirements for Close-Circuit Breathing Apparatus in its Guideline 0802 that has been written into the draft European Standard EN137 for Open-Circuit Compressed Air Breathing Apparatus for flame engulfment.

In this Directive, if special thermal loads for protective equipment cannot be excluded during tactical operation, the device must pass the flame engulfment test (similar to the NFPA flame engulfment test) described in Appendix D of the Directive.

In addition, this directive requires when using closed-circuit compressed air breathing apparatus, type positive pressure with mixed gas supply (N2, O2) with an oxygen content of ≥ 30% by volume in the breathing circuit, risks by oxygen emerging from a leakage in the mask cannot be excluded.

These devices must pass the oxygen flame engulfment test procedure described in appendix G of the Directive as follows:

• Simulate possible oxygen enrichment under a firefighter helmet according to EN 443 through a defined leakage in the respiratory protective mask (2.5 mm, 10mm above the right temple strap). The test set-up simulates real conditions by equipping the test head with real hair, a flame protection hood, and the respective neck curtains.
• Flame engulfment test is in accordance with Appendix D
• Device is attached to a test dummy and preheated in an oven at 90 ± 5˚ C for 15 minutes
• Complete unit is  exposed to direct flames for 10 seconds
• Test dummy, with the apparatus, is  lifted to 150 ± 5/0 mm and dropped
• During the entire test, the device is connected to a breathing machine. The pass/fail criteria are:
• Device must not continue to burn for more than 5 seconds
• No component that secures the device to the user’s body or secures the cylinder must come off or be displaced
• Breathing resistance as per EN 137 are met
• The test head must not continue to burn for more than 5 seconds

The Closed-Circuit Self-Contained Breathing Apparatus tested and witnessed by NIOSH/NPPTL personnel successfully passed all of the listed criteria.

In addition, the National Institute of Standards and Technology (NIST), Building and Fire Research Laboratory, Fire Research Division has provided a computational fluid dynamic (CFD) study of oxygen dissipation into the environment surrounding a respirator facepiece. For this study, 3-dimensional scans were taken of actual heads and masks for use in the CFD software. Leak geometries representing an imperfect seal were defined. Other variables included oxygen concentration fields and flow streamlines for multiple combinations of fuel and air in the surrounding environment, content of the leak, various breathing patterns, etc. Conclusions reached during the study were:

• Oxygen expelled through leak in respirator is propelled away from head region through advection and dissipates through diffusion
• Risk of flammable mixture near head is observed in 10 % propane environment
• This is an extreme environment (fuel-rich, near flammable mixture)
• In case of flammable environment, oxygen leak results in small, fuel-lean region near head
• In fuel-lean environment, oxygen further decreases fuel concentration

NIST Technical Note 1484, “A Computational Model of Dissipation of Oxygen from an Outward Leak of a Closed-Circuit Breathing Device” available at this link, http://fire.nist.gov/bfrlpubs/fire07/PDF/f07024.pdf chronicles the research work completed by NIST.

Input Sought from Stakeholders and Manufacturers

• Opinion on the current prohibition
• Supporting data to maintain, modify, or rescind the current prohibition
• What, if any, additional research is needed to support rescinding the prohibition
• Willingness to participate in a collaborative agreement with NIOSH/NPPTL to conduct research on this topic and support willing to provide
• Other comments on the subject
  

Public Comment Period

Comments will be accepted until 5:00 p.m. ET on September 30 , 2008

To submit comments regarding this draft publication, please use one of these options:

• Send comments by email.
  
  
• Fax comments to the NIOSH Docket Office: 513-533-8285
  
  
• Send by Mail to:
  NIOSH Mailstop: C-34
  Robert A. Taft Lab.
  4676 Columbia Parkway
  Cincinnati, Ohio 45226
  

Contact Person for Technical Information

Timothy R. Rehak at 412-386-6866 or email: ter1@cdc.gov

NIOSH Draft Documents for Public Review