Respirable crystalline silica (RCS), particles 100 times smaller than ordinary sand, is created during operations involving stone, rock, concrete, brick, block, mortar, and industrial sand. Exposure to RCS can occur when cutting, sawing, grinding, drilling, and crushing these materials. RCS exposure causes silicosis, an incurable and progressive disease, as well as lung cancer, other respiratory diseases, and kidney disease.
As long ago as the 1930s, then-Secretary of Labor Frances Perkins declared that by “control measures conscientiously adopted and applied” silicosis could be prevented. From its earliest days, OSHA has had standards limiting employee exposure to RCS.
However, permissible exposure limits (PELs) for RCS remain as adopted back in 1971. Current PELs are twice as high for construction and shipyards than under the general industry standard, and they are based on a method for measuring employee exposure that has been obsolete for forty years. During which time, multiple agencies (including the U.S. National Toxicology Program, the International Agency for Research n Cancer, and the National Institute for Occupational Safety and Health) have all identified RCS as a carcinogen.
Accordingly, OSHA has undertaken to modernize and strengthen the RCS standards, and published a Notice of Proposed Rulemaking on the subject in September 2013. OSHA’s rulemaking process can be seen as cumbersome and slow; another way of looking at it is that OSHA really does strive to “get it right,” from a technical standpoint, as well as in carrying out its mandate to protect workers, without imposing impossible burdens on employers. The process involved in formulating new OSHA standards includes a thorough review of industry consensus standards, and the underlying scientific and technical evidence. OSHA also carries out extensive outreach to the public and, especially, to employer and employee organizations and other interested parties. Considerable effort goes into soliciting participation in the rulemaking process, and comments on the proposed rule.
The pending proposals (one for general and maritime industries, the other for construction), following their publication in the Federal Register, were the subject of a comment period extended into February 2014, a live “webchat” in January, and public hearings in March and April.
Subject, naturally, to changes by the time the proposed rule becomes a final rule, the new construction standard will limit worker exposure to a new PEL of 50 μg of RCS per cubic meter of air, averaged over an 8-hour day. This new PEL will apply to all industries covered by the rule.
In addition, procedures for measuring exposure will be modernized, access will be limited to areas where silica exposures are high, and medical exams will be provided to workers with high silica exposures. Effective methods are prescribed for reducing exposures, and workers must be trained about silica-related hazards and how to limit exposure.
OSHA estimates that the proposed RCS rule will cost about $1,242 per year per workplace covered by the rule (but only about $550 for firms with fewer than 20 employees) while providing average net benefits of about $2.8 to $4.7 billion annually over the next 60 years.
OSHA estimates that the proposed rule, when fully implemented, will save nearly 700 lives, and prevent 1,600 new cases of silicosis per year.
OSHA does not expect the proposed rule to have any discernible impact on total U.S. employment.
Pending approval of the new rule, there are a number of basic engineering controls which you should consider implementing, if your trade works with brick, concrete slabs, block and pavers, etc.
Hand-held abrasive cutters (a/k/a cut-off saws, chop saws, or quickie saws) are used extensively — often without dust controls — to cut brick, concrete and other materials containing RCS. There are two widely-used engineering controls used to reduce dust exposures from the use of these saws. The first suppresses dust using water, typically from a portable pressurized tank or a hose, applied through nozzles to the blade of pneumatic, hydraulic, or gasoline-powered saws.
The other common method to control dust from cut-off saws is the installation of an exhaust hood or shroud surrounding the blade. The hood is connected by a flexible hose to an industrial vacuum cleaner. Adjustable hoods, capable of accommodating different cutting depths, are best.
Jackhammers, when used to break up concrete pavement, can also cause workers to be exposed to hazardous dust containing RCS. The most common method to abate this hazard is the use of a water-spray attachment. A low-flow, water-spray control typically will reduce dust exposure by 70% to 90%. So far as I have been able to find, there are no jackhammers that come supplied with water-spray units, and no commercially-available retrofit kits. However, parts and instructions to build a water-spray control can be found online at http://www.cdc.gov/niosh/docs/wp-solutions/2008-127/.
“Tuckpointing,” if you didn’t know, is the art of finishing masonry joints with a find, pointed ridge of mortar for decorative purposes. The grinder used for tuckpointing produces high concentrations of hazardous dust when used without dust controls. The local exhaust ventilation dust control employs a shroud enclosing most of the grinding wheel, a length of 2” diameter flexible hose, and an industrial vacuum cleaner. The vacuum cleaner should have a cyclonic pre-separator, to keep debris from reaching the final filters, and an air flow of 80 cubic feet per minute or more. This will typically achieve a reduction in hazardous dust of between 80% and 95%.
While there are, to be sure, other common tools and tasks that generate hazardous dusts containing RCS, the last one I’ll mention here is the use of grinders to smooth poured concrete surfaces. Without engineering controls, this activity can easily produce of 35 to 55 times the current NIOSH-recommended maximum exposure to RCS.
The control recommended for this application is conceptually similar to that used on the tuckpointing grinder: a ventilation shroud, a length of flexible hose, and a portable electric vacuum cleaner, that acts as the fan and dust collector. The vacuum cleaner should have a HEPA filter, a pre-filter or cyclone to increase the useful life of the HEPA filter, a motor drawing at least 10 amps (and a sufficient flow rate the capture the dust, and transport it to the vacuum source).
It’s desirable, too, that any vacuum device used in conjunction with grinding or other equipment have a filter replacement indicator, and the ability to clean and replace filters and full collection bowls or bags, without exposing the operator to dust.
It’s a safe bet that, when and as the proposed new OSHA standard for RCS becomes a final rule, OSHA inspectors will be highly attentive to enforcing the updated standard intended to reduce a long-recognized, serious hazard. You should tailor your training and internal monitoring practices accordingly.