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.


August 23, 1990

Mr. Bruce Gardener
Hydrous Dust Control Systems, Inc.

Dear Mr. Gardener:

This is in response to your letter of May 31, requesting an official opinion as to whether the Portam Process asbestos abatement equipment, which you propose to use for the removal of asbestos-containing pipe insulation, meets the intent of the occupational safety and health requirements at [29 CFR 1926.1101(g)(5)(i)].

The Occupational Safety and Health Administration (OSHA) does not approve or certify equipment or processes for use in the workplace. However, when we are provided with adequate information concerning a control method, we do offer an opinion regarding its effectiveness in achieving compliance with our requirements for employee safety and health. Therefore, this letter is not an approval or a certification of the Portam Process, but is an interpretation of our standards as they apply to the use of this system in United States workplaces.

The intent of OSHA's negative pressure enclosure requirement in paragraph [1926.1101(g)(5)(i)] for large scale removal operations is primarily to confine the asbestos being generated to the area within the enclosure and thus protect other employees and bystanders on the site from exposure to excessive levels of asbestos. Based on the data you have submitted, it appears that the use of your system, by employees trained pursuant to your training program, can prevent a release of significant asbestos contamination, thereby minimizing asbestos exposure of bystander employees.

[This document was edited on 12/01/01 to strike information that no longer reflects current OSHA policy.]

Because the purpose of performing removal work within negative pressure enclosures would be met by the use of your system, OSHA does not consider that such enclosures are necessary if the following conditions are met:




  1. All other provisions of OSHA's asbestos standard for construction must be complied with.
  2. Employees operating the system must be trained pursuant to the training program described in your submission.
  3. Regulated areas pursuant to [29 CFR 1926.1101(e)] must be demarcated and posted around the areas subject to removal with your system.
  4. Air monitoring must be conducted at each job site during and after the removal to assess the level of asbestos exposure to employees performing the removal and to those immediately outside the regulated area. Such monitoring would be essential for evaluating the effectiveness of the Portam system.

Please be aware that the effectiveness of your system can only be determined by the health and safety professional observing it in actual use under specific circumstances.

Also note that OSHA has published a proposed revision of its asbestos standards on July 20, 1990 (55 FR 29712), a copy of which is enclosed. Therein, OSHA is re-examining its regulatory policy concerning the continuation and/or expansion of negative pressure enclosure requirements for removal work. New technology, explicitly your system, is discussed on page 29717 of the Federal Register notice. OSHA indicates that it "will consider providing for new technology in the final standard to the extent supported by the record developed in this rulemaking."

The data you have submitted is now in the rulemaking record. We encourage you to submit further data to the rulemaking record and to participate in that proceeding.

This letter of interpretation will be superseded by a subsequent evaluation developed by the Agency based on a review of the entire rulemaking record developed in the pending asbestos rulemaking proceeding.

Please do not hesitate to contact us with any questions you may have.


Thomas J. Shepich, Director
[Directorate of Science, Technology, and Medicine]

[Corrected 06/23/08]