Occupational Exposures in Seismic Retrofitting Operations

ABSTRACT

The Hazard Section, Surveillance Branch of the National Institute for Occupational Safety and Health (NIOSH) conducted a study to assess exposures of construction workers to selected health hazards during seismic retrofitting of a historic mining engineering building at a university in California. The study was prompted by concerns regarding lead, noise, and other hazards typically associated with demolition and construction activities, and was conducted in cooperation with the university’s Office of Environment, Health, and Safety, as well as a general construction contractor and several special trade subcontractors. The mining building was one of four multi-storey laboratory/classroom buildings being retrofitted on the university’s campus at the time of this study. All of these retrofitting projects were funded by the Federal Emergency Management Agency (FEMA).

METHODS

In April 2000, a preliminary observational walkthrough of the building was conducted to identify health hazards and associated occupations for subsequent quantitative exposure assessment. Bulk samples of selected building materials (i.e., concrete, brick mortar, and plaster) were collected and analyzed to confirm the presence of crystalline silica (quartz).

Based on information gathered from the walkthrough, special trade subcontractor in 11 occupational groups having potential exposure to crystalline silica, lead, diesel exhaust, and noise were selected for quantitative assessment during a three-day follow-up survey conducted in June 2000. Worker exposures were quantitatively evaluated by collecting integrated personal and/or area air samples and noise dosimetry measurements in accordance with the sampling strategy presented in Table I. In a few cases, area air samples were collected in the general vicinity of the worker, when the worker indicated that he would not wear the sampling equipment. Most of the samples were collected over a full shift (i.e., 7 to 8 hours); samples with durations less than 7 hours were collected for the duration of a particular task.

Lead

The personal breathing zone (PBZ) air samples for lead were collected using NIOSH Method 7082. The sampling and analysis method was modified by the use of preweighed 37-millimeter (mm) polyvinyl chloride (PVC) 5-micrometer (μm) pore-size membrane filters at a flow rate of 3 liters per minute (Lpm). The PVC filters were used for gravimetric analysis; the sample results are not reported herein because they were unremarkable. The analytical method was modified for nitric acid/microwave digestion of the PVC filters. If lead was not detected by this method, the sample was subsequently analyzed by the more sensitive NIOSH Method 7300. Limits of detection (LOD) and quantitation (LOQ) for samples analyzed by NIOSH Methods 7300 and 7082 ranged from 0.0002 to 0.005 and from 0.0006 to 0.020 milligrams per sample (mg/sample), respectively.

Crystalline Silica

The PBZ samples for respirable crystalline silica were collected in accordance with NIOSH Method 7500, using 5.0 μm pore-size PVC filters and a 10-mm nylon cyclone to remove the non-respirable fraction (> 4 μm mass-median aerodynamic diameter [MMAD]) at a flow rate of 1.7 Lpm. Filters were analyzed for quartz using x-ray diffraction according to this same method. The LOD and LOQ for the analysis were 0.01 and 0.03 mg/sample, respectively.

Diesel Exhaust

The PBZ and general area air samples for diesel exhaust were collected and analyzed in accordance with NIOSH Method 5040. The air samples were collected on 37-mm quartz-fiber filters, utilizing a high-flow respirable-thoracic cyclone (BGI Inc., Waltham, MA) with an MMAD cut size of 6 μm, at a flow rate of 3 Lpm. The air samples were analyzed for elemental carbon (EC), a surrogate for diesel exhaust particulate exposure. Three air samples (one per day) were collected on the roof of the building, away from any diesel emission point sources, to asses background concentrations. The LOD and LOQ for the analysis were 0.008 and 0.026 mg/sample, respectively.

Noise

Occupations and tasks with noise levels >= 85 A-weighted decibels (dBA), measured during the first day of the follow-up evaluation using a sound level meter (Quest Electronics, Model 215, Oconomowoc, WI), were selected for personal and area dosimetry. Noise dosimetry was conducted using noise dosimeters (Quest Electronics, Model Q-300, Oconomowoc, WI), which were worn by the workers, with the microphone positioned on the shirt lapel/collar, directly below the ear. When personal dosimetry was not possible (2 of the total 19 samples),the dosimeter was placed in the immediate vicinity of the worker. The dosimeters were programmed to measure noise levels in two separately calibrated channels, one using a 3-dB exchange rate and an 80-dB threshold for comparison to the NIOSH Recommended Exposure Limit (REL), and the other using a 5-dB exchange rate and a 90-dB threshold for comparison to the OSHA Permissible Exposure Limit (PEL).  In this study, these two channels are subsequently referred to as the REL channel and the PEL channel, respectively. At the end of each work shift, stored data were downloaded to a personal computer for evaluation.

RESULTS

Air sampling results for lead, crystalline silica, and diesel exhaust by occupation, observed task(s), sample type, number of samples collected, and sampling duration are presented in Table II. Personal and area noise levels, measured in the REL and PEL channels, are presented in Table III by occupation, observed task(s), sample type, number of samples collected, and sampling duration. Maximum noise levels for each of these samples are also reported in Table III. All air sampling and noise results were compared to applicable NIOSH RELs, OSHA PELs, and American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs).

Lead

Lead concentrations for the eight PBZ samples ranged from trace (i.e., greater or equal to the LOD but less than or equal to the LOQ) to 0.05 milligrams per cubic meter of air (mg/m3), as shown in Table II. The highest concentration, 0.05 mg/m3, equivalent to the PEL, REL, and TLV, was from a chipper operator during removal of lead-contaminated concrete and plaster from the sublevel ceiling. Lead exposures of the welder during welding of structural steel ranged up to 0.024 mg/m3 over a sampling period of approximately two hours.

Crystalline Silica

Silica concentrations for the 15 PBZ samples ranged from nondetectable (ND) to 0.27 mg/m3 (Table II). Occupations with exposures exceeding the REL and TLV of 0.05 mg/m3 included chipper operators; lead abatement workers; and the rebar installer during dry-drilling of holes in steel, concrete, and bricks. However, sample results did not approach 20 percent of applicable PELs, calculated as 10 mg/m3/(%Silica [%quartz for that sample] + 2). Nondetectable or trace levels were measured for the core drill operator during wet drilling of steel, brick, and concrete, and for the construction equipment operators.

Diesel Exhaust

Diesel exhaust (as EC) concentrations ranged from ND to 0.08 mg/m3 (Table II). The four PBZ samples from operators of various pieces of diesel-powered equipment ranged from trace to 0.04 mg/m3. Four area samples, collected to assess exposures of construction laborers who were working in the immediate vicinity of diesel-powered equipment, ranged from ND to 0.08 mg/m3. Samples collected from the building carpenter, construction laborer, and supervisors were ND. Because NIOSH and ACGIH consider diesel exhaust a potential human carcinogen, it is prudent to maintain exposures at or below the lowest feasible concentration (LFC). For purposes of this study, the LFC (i.e., NIOSH REL) was equivalent to ambient background concentrations, which were all nondetectable, i.e., less than 0.008 mg/m3. The sampling results indicated that equipment operators were exposed to diesel exhaust levels of up to five times the NIOSH REL, and that the construction laborers’ exposures ranged up to 10 times the REL (worst-case scenario, given that none of the workers remained in the sublevel for the entire shift).

Noise

Personal and area TWA and maximum noise levels, for both the PEL and REL channels, are presented in Table III, by occupation and observed task(s). Noise exposures in the PEL channel ranged from65 to 108 dBA, with eight personal samples at or above the PEL. Occupations with exposures at or above the PEL included the pneumatic chipper operators, rebar installer, construction equipment operators, roofers, and lead abatement workers. In the REL channel, noise levels ranged from 80.8 to 112 dBA, with 16 of the personal samples and one area sample at or above the REL. Occupations with exposures at or above the REL included building carpenters, brick masons, core drill operators, and those that exceeded the PEL. Maximum slow-response noise levels ranged from 105 to 138 dBA; none of the samples exceeded the REL and PEL of 140 dBA.
