Silica and noise exposure during installation of fibercement siding

ABSTRACT

This case study helps to characterize potential health hazards from the installation of fibercement lap siding. Safety inspectors from the authors' state OSHA office had noticed visible dust from the cutting of fibercement board during their inspections of construction sites. As a result, industrial hygiene inspectors sampled for respirable crystalline silica and also noise, as the power tools used to perform the cutting presented the potential for excessive exposure. Additionally, agency records were searched for other existing sampling data from siding worksites using fibercement board. This report presents the results of the sampling and discusses methods of controlling exposure. The authors were unable to identify another publication assessing the silica and noise hazards for this emerging construction activity with fibercement lap siding.

METHODS

Data for this report were extracted from existing records of Washington Industrial Safety and Health Act Services (WISHA), the State of Washington OSHA program. WISHA has been an approved OSHA state plan since 1973 and is administered by the state's Department of Labor and Industries.

WISHA inspection records of fibercement board installation worksites were initially identified by the authors' own inspection activity. An effort to identify additional statewide inspections was completed by searching the WISHA industrial hygiene laboratory's data bank for inspections in construction with silica sampling results spanning the years 1996 through 2002. The agency's industrial hygiene laboratory maintains an electronic databank of analytical results submitted by WISHA industrial hygienists. No additional fibercement board inspections were found. The WISHA inspection reports of siding worksites were reviewed for identified hazards, including silica and noise, siding practices, materials, tools, and control methods used by contractors and workers and any violations recorded.

A search was also performed for silica sampling data for fibercement board worksites receiving a WISHA consultation. Industrial hygiene consultants and their supervisors were asked to provide sampling information and data without any employer or employee identifiers, in accordance with state policy and procedures. One data set was reported and included in this report.

Respirable silica sampling was performed by WISHA staff in accordance with the Department's Technical Manual. Sampling pumps were pre- and post-calibrated. Respirable samples were either taken with an MSA 10-mm nylon cyclone at a flow rate of 1.7 L/min or an SKC aluminum cyclone at 2.5 L/min. The cyclones were fitted with 37-mm filter cassettes and pre-weighed 0.8 μm PVC filters. Both types of cyclones are accepted by the agency for determining worker exposure to airborne respirable silica for comparison with the agency's PEL. The filter cassettes were placed in the workers' breathing zones to obtain samples representative of their personal exposure.

Samples were analyzed by the agency's laboratory, which is accredited by the American Industrial Hygiene Association (AIHA). The filters were re-weighed to determine respirable total particulate and subjected to analysis for silica. Crystalline silica was analyzed by either Fourier transform infrared analysis (FTIR) or by X-ray diffraction (XRD). Results were reported as milligrams of crystalline silica (quartz) per cubic meter of air. The sampling and analytical error (SAE) for both the 10-mm nylon cyclone and aluminum cyclone using the FTIR analytical method was 0.25. The SAE for the aluminum cyclone using the XRD analysis was 0.16.

Noise sampling was completed in accordance with the WISHA Technical Manual. Dosimeters were pre- and post-calibrated and workers wore the dosimeters throughout their work shift with the microphones, equipped with windscreens, typically placed on the worker's shoulder in order to obtain a personal sample. Dosimeter types included Dupont MK-1s and MK-3s set at an 80 dB cutoff and 5 dB exchange rate with a criterion level of 90 dBA equal to 100%.

RESULTS

Contents of Fibercement Siding

The manufacturers' material safety data sheets (MSDSs) for the siding products in use at the visited worksites reported the chemical content as calcium silicate, crystalline silica, cellulose fiber, and other ingredients at less than 10% by weight (non-asbestos fibercement). The percent crystalline silica in the two siding products is shown in Table I and ranged from 35 to 55%. The variability in the amount of silica is likely due to the varying percent of quartz in the sand and varying amounts of sand used in the two products. Crystalline silica exposure was considered to be the primary chemical exposure due to its high concentration in the material and significantly low airborne exposure limit relative to the other chemicals.

Installation of Fibercement Siding

The fibercement siding was cut and installed in a similar fashion as that of wood lap siding. The gray primered boards were cut crosswise, ripped lengthwise, and cut in angles or curves as needed to install the siding around windows, doors, vents, and other structural items. The boards typically were cut at ground level by an assigned cutter and handed to an installer. The installer used a pneumatic nail gun to affix the siding. Occasionally, the installer also cut boards.

The primary tool used to cut fibercement boards was an electric-powered circular handsaw as shown in operation in Figure 1. The saws were operated dry, creating a visible dust when a board was cut. Saw blade selection varied, with most having a diamond-tooth blade recommended for fibercement by the saw manufacturer. On a few sites, the cutter or installer used an electric powered shear infrequently. The installer occasionally used the shear to make a cut at the point of installation or while on a scaffold. Figure 2 depicts a cutter using a hand shear to cut a board lengthwise. The thin section cut from the board forms a curl of material in front of the scissors blade.


Employers and Worksites Visited

Six of the seven contractors were found to employ from four to seven employees (employer data was unavailable for one of the contractors). Each typically assigned one employee the primary duty of cutting the boards. In two instances, the owner designated himself as the cutter on the day inspected. Four of the contractors were listed in the department's records with the Standard Industrial Classification (SIC) code 1761 (Roofing, Siding, and Sheet Metal Work), one was listed under the SIC code 1751 (Carpentry Work), and another under 7349 (Building Cleaning and Maintenance Services, not Elsewhere Classified). Siding was installed on single-family homes and apartment buildings.

Exposure to Crystalline Silica and Control

Cutter exposure to respirable crystalline silica in excess of the WISHA regulatory limit was found at three of the seven worksites where fibercement was being installed, as shown in Table II. The cutter for employer A would most likely have experienced an overexposure if not for unplanned work delays that reduced the length of exposure on the day sampled.

The exposure results for respirable total particulate in every case were below the state's limit of 5.0 mg /m3 as an 8-hour TWA. The highest value was 1.7 mg/m3 as an 8-hour TWA for a worker with company B.

At all worksites, the primary contributor to silica exposure was observed to be dust generated by the dry operation of the circular handsaw, although other variables could affect the exposure as well. All cutters worked outdoors in clear weather, and not under structures or near walls that could concentrate or suspend the dust near the cutter. Installers or other employees were not sampled due to their distance from the cutting operation and improbability of being exposed in excess of the regulatory limit.

The six contractors whose workers were sampled by the WISHA compliance inspector received violations related to silica exposure. Companies B and C received violations for lack of administrative or engineering control as a result of the recorded overexposure to crystalline silica. Company F was informed that control would be required if employees performed the cutting instead of the owner as sampled. All six of the inspected companies received a violation for not providing hazard communication training for silica exposure and not having an MSDS for the fibercement boards.

Respirators were used by all sampled workers, varying from a disposable filtering facepiece rated for dusts to an elastomeric half-face respirator with HEPA cartridges. None of the inspected contractors had established an effective respirator protection program. Each contractor lacked employee respirator training and fit tests. Three workers had beards that interfered with the seal of the respirator.

Comparison of Cutting Tools

Sample data was also available for two primary tools used to cut fibercement boards, as shown in Table III. The comparison shows the possible contribution that each tool can have on the cutter's silica exposure, with full shift exposure depending on the manner and length of time the tool is used.

Under test conditions, a cutter's exposure was sampled while he repetitively aligned and cut four stacked fibercement boards using a circular handsaw outdoors. The test covered a 15-min period to ensure enough samples for analysis. Actual sawing of stacked or single boards at the inspected worksites was not continuous but took seconds to minutes at a time, followed by periods without cutting. The total sawing time in a day by a cutter was estimated to vary from about 5 to 20 minutes.

Sampling for personal exposure during the use of the shear was performed for the repetitive cutting of single fibercement boards during the use of the tool at an indoor industrial site. The shear can cut only a single board at a time. The number of cuts completed during the sampling was estimated to be equivalent to the amount used to side three houses. The shear at siding worksites would not undergo as frequent or continuous operation in a work shift even if used instead of the circular handsaw.

Although representing only a few data points and considering that the comparison was between the saw cutting four boards and the shear one, the data in Tale III does demonstrate that the shear produces significantly less silica exposure. The sampling data is consistent with visual observations of the dust levels between the two tools.

Noise Exposure

Noise monitoring was also performed for cutters on five of the worksites inspected as shown in Table IV. Four of the five cutters sampled had noise exposures in excess of the WISHA limit of a 50% dose or 85 dBA as an 8-hour TWA. Exposure at or above this limit requires both the use of hearing protectors and the implementation of a hearing conservation program in the State of Washington. The circular handsaw was found to be the primary source of the noise. Hearing protection was worn by each sampled worker.

No hearing conservation program violations were identified for the contractors. Cutters were found not employed long enough for audiograms to be required under the hearing conservation standard. Other workers were deemed unlikely to be exposed in excess of the state's limit for noise and were not included in the sampling.
