The Occupational Safety and Health Administration, responding to a request of the National Forest and Paper Association, has updated its compliance guidance on how inspectors are to evaluate accumulated levels of low bulk-density combustible dusts for enforcement purposes. The guidance (https://www.osha.gov/dep/enforcement/Combustible_Du sts_04212015.html) was released by OSHA on May 22.

The Association asked OSHA to explain to the agency’s inspectors that they should consider the unique characteristics of a dust ‒ such as its bulk density ‒ instead of basing assessments on whether dust accumulation simply surpasses 1/32 of an inch (about the diameter of a paper clip), an OSHA spokesperson told Bloomberg BNA.

OSHA’s compliance guidance for its seven-year-old National Emphasis Program (NEP) for combustible dust references 1/32-inch dust accumulation levels. However, OSHA made clear in the latest guidance that this accumulation thickness is based on certain assumptions. These include the uniformity of the dust layer covering the surfaces and a material bulk density of 75 pounds per cubic foot (lb/ft3 ). The 2013 update of National Fire Protection Association consensus standard 654 includes a mathematical calculation for determining when the dust accumulation level may exceed the layer depth criteria of 1/32-inch for materials with bulk density less than 75 lb/ft3 , the guidance noted.

Thus, inspectors should consider the bulk density of the dust prior to determining if there has been a violation of the housekeeping standard (29 CFR § 1910.22) or the materials handling and storage standard (29 CFR § 1910.176). For tissue paper dust, fabric fibers, and other low-density dusts (i.e., less than 75 lb/ft3 ), the guidance advises inspectors to collect samples for laboratory analysis of bulk density, provided that the accumulation level is greater than ¼-inch extending over 5 percent of the floor area of a room or building, or 1000 ft2 , whichever is less. Sample collection steps are provided, and inspectors are instructed to send samples to OSHA's Salt Lake Technical Center in Utah.

However, the guidance also makes clear that samples for bulk-density determinations are not necessary for dust accumulations exceeding one inch in depth and extending over the same floor area. In those cases, information on the approximate bulk densities of the combustible dust may be obtained from the employer, the Internet, or other sources. Those numbers then may be used to determine the approximate values of the dust accumulations for citation purposes, according to the guidance.

OSHA believes the outcome of most inspections will remain unchanged by the new guidance. According to the OSHA spokesperson, bulk-density determinations may not be an issue in many cases because inspectors normally find combustible dust accumulations levels far exceeding hazardous levels. Only cases involving light dusts could be affected, because of the importance of bulk density in determining if hazardous accumulations of dust are present. OSHA began a controversial rulemaking for combustible dust in 2009 and held meetings in 2010. More recently, the agency proposed conducting a Small Business Regulatory Enforcement Fairness Act review in February 2016.