The question that comes up frequently in asbestos training classes is whether a glovebag fulfills the critical barrier requirements of OSHA or not. Glovebag means not more than a 60 × 60 inch impervious plastic bag-like enclosure affixed around an asbestos-containing material, with glove-like appendages through which material and tools may be handled. The definition of a critical barrier is one or more layers of plastic sealed over all openings into a work area, or any other similarly place physical barriers sufficient to prevent airborne asbestos in a work area from migrating to an adjacent area.
The preamble to the OSHA Asbestos Standard in 1994 gives us some background information. They say that Class I work such as the removal of TSI or friable surfacing ACM or PACM must be performed using procedures in paragraph (g)(4) and using a control method which is listed in paragraph (g)(5). Critical barriers are a (g)(4) procedure, glovebags are a (g)(5) control method. This is an important distinction. If another control method is used, or if a listed control method is modified, the standard in paragraph (g)(6) requires that a certified industrial hygienist (CIH) or licensed professional engineer who is a project designer certify the control method using the criteria set out in the regulatory text.
The requirements of (g)(4) are: for Class I jobs, preparation must be supervised by a competent person, dropcloths must be used, and HVAC systems must be isolated. The area must be set up using critical barriers, either as part of a negative pressure enclosure system or as a supplemental barrier to another listed system, which isolates the asbestos disturbance in a different way. Other barriers or isolation methods may be used to prevent asbestos migration. The effectiveness of such methods must be proven by visual inspection and clearance or perimeter monitoring. OSHA believes that the size of the removal job alone does not predict the risk to workers. However, if a job is smaller there is less chance that isolation barriers provided by glovebags or gloveboxes will fail. This refers to the requirement that additional critical barriers are only required for glovebag projects over 25 linear feet.
Continuing with the preamble, OSHA was reluctant to limit glovebag removals without critical barriers only to maintenance projects where, as NIOSH noted, it is more likely that crews will be untrained. Rather, OSHA has followed the lead of some states which allow removals involving fewer than 25 linear feet of TSI or 10 square feet of other material to be handled without critical barriers, unless the glovebags or enclosures lose their integrity, or where a negative exposure assessment has not been produced.
Critical barriers are required in addition to glovebags for projects less than 25 linear feet if there is no negative exposure assessment. Such projects are Class I removals. Workers who perform them must be trained in an EPA accredited training course or equivalent. OSHA believes that the workforce performing these relatively minor removals is the same workforce performing major removals. Thus, the job will be well conducted and critical barriers will be unnecessary. In addition, where the employer cannot demonstrate that a Class I job is unlikely to over-expose employees, the employer must ventilate the regulated area to remove contaminated air from the employees’ breathing zones.
Continuing with the language of the OSHA preamble to the asbestos standard, paragraph (g)(5) lists control methods that OSHA evaluated during this rulemaking. The agency finds that using these methods pursuant to the limitations and specifications in the paragraph is likely to effectively control employee exposures when performing Class I work.
The first control system listed for Class I work is the Negative Pressure Enclosure System, or NPE. The extent to which OSHA should require these systems for major asbestos work was a remanded issue. OSHA has found that NPEs, when constructed and used according to the criteria in the standard, can effectively protect employees within and outside the enclosure.
Other listed systems may be used for Class I work under stated limitations. Paragraph (g)(5) sets out these limitations. These systems are: glovebag systems, negative pressure glovebag systems, negative pressure glovebox systems, the water spray process system, and a mini-enclosure system. OSHA emphasizes the use of the term "system". Each method consists of tangible materials and devices, and procedures and practices. All the listed elements must be complied with before OSHA's finding of effectiveness is relevant. Other unspecified control methods — or "alternative control methods" – may be used if additional notification is given to OSHA, and if a specially trained project designer or CIH certifies that the controls will be protective.
Class I work i.e., the removal of TSI and/or surfacing ACM or PACM must be performed using procedures in paragraph (g)(4) and using a control method which is listed in paragraph (g)(5) of the standard. If another control method is used, or the listed control method is modified, the standard paragraph (g)(6) requires that a certified industrial hygienist (CIH) or licensed professional engineer who is a project designer certify the control method using the criteria set out in the regulatory text.
The takeaway from all of this is that if you have a glovebag job that is Class I, and the job is more than one glovebag, which is 60 inches by 60 inches as specified for Class III, and you're less than 25 linear feet or 10 square feet, OSHA does not require critical barriers unless you don't have a negative exposure assessment. Above 25 linear feet for glovebag projects or 10 square feet, the standard requires that even if you have glovebags, you must have critical barriers. If there is not a feasible way in OSHA language to put up these critical barriers, then the standard requires perimeter monitoring, with each barrier monitored with a PCM sample with results back within 24 hours and the results showing you're below the clearance levels or are below background levels. But above 25 linear feet, glovebags have to be supplemented by critical barriers or their equivalent, whether or not you have a negative exposure assessment.