Friday, January 13, 2006

Silica In Construction

Excessive exposure to silica in the US construction industry.

Ann Occup Hyg. 2003 Mar; 47(2):111-22.

Rappaport, S. M.; Goldberg, M.; Susi, P., and Herrick, R. F.

Abstract: Exposures to respirable dust and silica were investigated among 36 construction sites in the USA. Personal measurements (n = 151) were analyzed from 80 workers in four trades, namely bricklayers, painters (while abrasive blasting), operating engineers and laborers. Painters had the highest exposures (median values for respirable dust and silica: 13.5 and 1.28 mg/m(3), respectively), followed by laborers (2.46 and 0.350 mg/m(3)), bricklayers (2.13 and 3.20 mg/m(3)) and operating engineers (0.720 and 0.075 mg/m(3)). Mixed models were fitted to the log-transformed air levels to estimate the means and within- and between-worker variance components of the distributions in each trade. We refer to the likelihood that a typical worker from a given trade would be exposed, on average, above the occupational exposure limit (OEL) as the probability of overexposure. Given US OELs of 0.05 mg/m(3) for respirable silica and 3 mg/m(3) for respirable dust, we estimated probabilities of overexposure as between 64.5 and 100% for silica and between 8.2 and 89.2% for dust; in no instance could it be inferred with certainty that this probability was <10%.>


BrooklynDodger Comments: A forgotten story in occupational health is how NIOSH published a criteria document on silica in 1974 [] recommending an exposure limit of 0.05 mg/M3, based on pulmonary function test decrements. The Dodger remembers that maybe the PFT changes achieved statistical significance at lower cumulative exposures than x-ray changes. That was before silica was known to be a human carcinogen, and before we knew that an acceptable exposure level should be 1/10 of the NOAEL. NIOSH also recommended the boiler plate exposure monitoring and medical surveillance.

The Mort Corn OSHA issued an ANPR for silica [and lead]. Lead went forward under Eula Bingham. Cotton dust, arsenic, vinyl chloride...Silica went nowhere, although a lot of foundries and other facilities were cited for overexposures at 100 ug/M3. [respirable] Now, a proposal for silica awaits release from OMB.

Now the guru of statistical air sampling, Steve Rappaport publishes data showing rampant over exposures in the construction trades. These results are substantially higher than the dust exposures measured during the world trade center recovery operation.

Steve also quotes the ACGIH values of 3 mg/M3 for non crystalline silica dust and .05 for silica, in contrast to the OSHA PEL's of 5 and 100.

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