Determinants of respirable crystalline silica (RCS) exposures
among stoneworkers involved in stone restoration work.
B. Healy1, Marie A. Coggins1, Martie Van
Tongeren2, Laura MacCalman2, Ken Moore3
of Physics, National University of Ireland, Galway, Galway, Ireland, 2Institute
of Occupational Medicine, UK, 3 Office of Public Works, Jonathan Swift Street, Trim, Co Meath, Ireland.
Crystalline silica occurs as a
significant component of many traditional materials used in restoration stonework
such as sandstone and other commonly used building materials. When these
materials are processed through activities such as grinding and cutting,
particulates containing varying quantities of RCS are released into the
occupational environment. Exposure to dust containing RCS can result in the
development of silicosis, an irreversible debilitating lung disease and may
also lead to the development of lung cancer.
The aim of this research is
to i) quantify the respirable crystalline silica exposure of a group of
stoneworkers involved in the restoration and maintenance of heritage properties
in Ireland and ii) to identify the main determinants of
exposure among this occupational group. These results will facilitate the
development of technical interventions in areas of high exposure risk within
this occupational group. †
An exposure assessment has
been carried out over a 3 year period amongst a group of stonemasons and stone
cutters involved in the restoration and maintenance of heritage properties.
Personal air samples (n=113) with
corresponding contextual information in various stone restoration jobs were
collected. Similar exposure groups (SEGs) were formed based on tasks and
materials used. Descriptive statistics were generated for the SEGs. Exposure data
were analysed using multiple linear regression analysis to identify significant
determinants of exposure and to investigate their contribution to the
individualís mean exposure. Mixed effects models were used to identify
determinants of exposure and to evaluate the between- and within-worker variability
in exposure among stoneworkers and variability associated with depots.
Currently, 113 personal exposure samples
have been collected. The RCS exposure measurements ranged from 0.02 mg/m3-
2.98 mg/m3 (8hr-TWA). In many cases worker exposure to RCS exceeded the
occupational exposure limit value (OELV) of 0.1mg/m3 (8hr- TWA). Multiple linear regression identified a significant
relationship between RCS (8hr- TWA) exposure and different materials, tasks and level of enclosure (P <0.001). Task contributed the most to individual mean RCS exposure
(R2 = 43.2, P <.001) where exposure was
higher for the tasks of shaping and dry cutting. Task was followed by material (R2 = 36.8, P
where RCS was higher for tasks involving sandstone. The
Upper Confidence Limit of the arithmetic mean (UCL1,95% ) exposure
for both tasks of cutting and shaping of sandstone was found to be 1.24 mg/m3
which is above the occupational exposure limit value of 0.1mg/m3
and is deemed unacceptable. In combination, task, material and level
of enclosure together accounted for 72% of the variation in RCS exposure.
Results from the mixed effects models also revealed that task and material are strong predictors of
RCS exposure within this occupational group. The results indicate that the
tasks of dry cutting and shaping sandstone are predictors of increased exposure
to RCS dust. Task such as wet cutting and repointing and working with materials
such as limestone, lime mortar and granite were associated with decreased
exposure to RCS dust. The between depot and between worker within depot
variance components were reduced by 64% from 1.096 in the random effects model
to 0.39 in the mixed effects model and 86% from 1.125 in the random effects
model to 0.15 in the mixed effects model respectively when task and material
were taken into account. These results suggest that the differences in mean
exposures between depots are more prominent than differences in mean exposures
between workers within depots Tools and materials which create excessive exposure to RCS dust have
been targeted for control and a technical intervention has commenced in order
to reduce exposure to as low as practically possible.† Post intervention exposure data and results
from the mixed effects models will be presented.
Initial analysis of the exposure
data collected to date shows that workers can be regularly over exposed to RCS dust
when working with sandstone, as compared to the OELV. Results show that task and material are strong predictors of RCS exposure
within the occupational group restoration stoneworkers.