«This Survey Report and any recommendations made herein are for the specific facility evaluated and may not be universally applicable. Any ...»
This Survey Report and any recommendations made herein are for the specific facility evaluated and may not be universally applicable. Any
recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved. Additional NIOSH
Survey Reports are available at http://www.cdc.gov/niosh/surveyreports.
IN-DEPTH SURVEY REPORT:
STYRENE AND NOISE EXPOSURES DURING FIBER REINFORCED PLASTIC
BOAT MANUFACTURINGAT LARSON/GLASTRON INC.
LITTLE FALLS, MINNESOTA
REPORT WRITTEN BY:
Rebecca M. Valladares Michael Gressel, Ph.D., CSP H. Amy Feng, M.S.
Chuck Kardous, M.S., P.E.
Leo M. Blade, CIH Duane Hammond Daniel Farwick
April 2005 REPORT NO: EPHB 306-11a
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
All mentioned above:
NIOSH, Cincinnati, OH EMPLOYER REPRESENTATIVES Jeffery E. Melby, P.E.
CONTACTED: Vice President Environmental & Safety
A survey was performed to assess the occupational exposures to styrene and noise, and to evaluate the effectiveness of engineering controls for styrene in two distinct fiberglass reinforced plastic (FRP) boat manufacturing plants. The primary objective of this study was to quantify the exposures occurring in both an open and closed mold plant and to evaluate the installed engineering controls to reduce styrene exposure. The effectiveness of the styrene controls examined in this study was evaluated by measuring styrene personal breathing-zone and general-area samples during typical work shifts. The ventilation system in Plant 7, the closed mold plant, appeared to be relatively effective for controlling the amount of styrene-area vapors released into the air. Results showed this closed mold system controlled styrene vapor concentrations in the air from 0.14 parts per million (ppm) in areas upwind of the styrene emitting source, to 3.7-12.2 ppm inside the actual Virtual Engineered Composites (VEC) cells. Personal breathing-zone exposures for employees working in the molding areas ranged from non-detected to 20.7 ppm.
While these full shift samples were not above the NIOSH Recommended Exposure Level (REL), a comparison between the laminators who spray gelcoat and the loaders who do not, suggests short-term exposures during gelcoat spraying may be a concern. Area samples taken in the resin and gel coat storage rooms showed concentrations, ranging from non-detected to 39.0 ppm. Results for the open mold plant (Plant 6) were markedly different, indicating the installed control systems were not as effective in controlling styrene exposures. The personal breathing-zone exposures, in Plant 6, ranged from 22.8 to 103 ppm with geometric mean exposures ranging from 30.3 ppm (gelcoater) to 82.8 ppm (hull roller). The general-area concentrations measured ranged from 2.2 ppm in the northeast region to 28.7 ppm in the southwest region. Upgrades to the local exhaust ventilation system in Plant 6 should be a priority. The current ventilation system is not working to its maximum potential and thus allowing workers to be exposed to concentrations of styrene vapors above the NIOSH REL and near the OSHA PEL. In Plant 7, the source(s) of the fugitive styrene emissions in the resin and gel coat storage rooms should be identified and controlled. The exposures measured in the gelcoat room are assumed to be a result of agitating, pumping, and handling of gelcoat. Improvements to the local exhaust ventilation systems in the VEC cells should also be considered to address the potentially high short-term exposures. Regarding the noise measurements, all personal and area measurements taken in Plant 6 and 7 were below the OSHA Permissible Exposure Level (PEL) of 90 dBA. The gelcoater and gunner exposures are above the NIOSH Recommended Exposure Level (REL) and OSHA Action Level (AL) of 85 dBA. In a number of cases, measured noise levels indicated that there was great variation in workers’ noise exposures. Certain phases of the job are noisier than others or there may be an impact/impulse component to the noise exposure. Sound exposure levels in Plant 6 are on average 2-4 dBA higher than the VEC plant 7 levels (an increase of 3 dB is a doubling of the sound energy). The results of the noise monitoring suggest the need for noise control of tasks that generate excessive exposures in Plant 6. If styrene and noise exposures are not reduced, the audiometric monitoring of employees that are exposed simultaneously to noise and styrene is recommended, as detailed in the ACGIH notes in its Noise Section (ACGIH, 2004).
iv Introduction The National Institute for Occupational Safety and Health (NIOSH) is part of the Centers for Disease Control and Prevention (CDC) in the Department of Health and Human Services (DHHS). NIOSH was established in 1970 by the Occupational Safety and Health (OSH) Act, at the same time that the Occupational Safety and Health Administration (OSHA) was created in the Department of Labor (DOL). The OSH Act mandated NIOSH to conduct research and education programs separate from the standard-setting and enforcement functions conducted by OSHA. An important area of NIOSH research involves controlling occupational exposure to potential chemical and physical hazards.
On September 19-24, 2004, researchers from the Engineering and Physical Hazards Branch (EPHB) of the Division of Applied Research and Technology (DART) conducted an in-depth survey at Genmar Holdings, Inc. Larson/Glastron facility in Little Falls, Minnesota. The primary purpose of this survey was to assess the occupational exposures to styrene vapor in air and to evaluate the effectiveness of engineering exposure-control measures during fiberglass reinforced plastic (FRP) boat manufacturing operations. A secondary objective was to evaluate noise exposures during these operations. Production of fiberglass boats in Plant 7, the closed-mold plant, took place in three self-contained cells using a computer-controlled, automated, closed-mold process called Virtual Engineered Composites (VEC). The open-mold operation, Plant 6, differed greatly from the closed-mold process in terms of both equipment and labor required for production. In both Plants 6 and 7, personal and general area samples were collected for noise and styrene vapor exposures. For this report, effective engineering controls are those that maintain styrene exposures below the occupational exposure limits—the NIOSH recommended exposure limit (REL), the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV®), or the OSHA permissible exposure limit (PEL). This report explains the study methods, results, and provides recommendations for protecting workers more effectively.
Styrene Usage and the Hazards of Exposure to Styrene and Noise The major chemical component of concern in terms of occupational exposures in the FRP process is styrene. The thermoset polyester resin used at this facility was 32.25% styrene content by weight. Styrene is an important reactive diluent for polyesters because it reduces the viscosity of the polyester mixture making it thinner and more capable of coating fiber reinforcements. Low viscosity also allows the reactive sites on the molecules to interact. Styrene is an active diluent, meaning it will react in the free radical crosslinking reaction. Cross-linking is the attachment of two chains of polymer molecules by bridges composed of molecular, in this case styrene, and primary chemical bonds. It produces a solid that is impervious to most solvents, petroleum, and other chemicals found in the marine environment. Since styrene is consumed as part of this reaction, there is no need for removal of the diluents after the part is formed; however, due to the high volatility of styrene, vapors from the application and curing process may pose an inhalation exposure hazard for workers near the process.
Some of the health effects of low-level styrene exposure include ototoxicity in workers and experimental animals. Styrene exposure can cause permanent and progressive damage to the auditory system in rats even after exposure has ceased.1,2 Styrene has been shown to be a potent ototoxicant by itself, and can have a synergistic effect when presented together with noise or ethanol.3,4,5,6 In addition, studies have shown that styrene exposures were linked to central and peripheral neurologic,7,8,9 optic,10,11 and irritant12 effects in humans when workplace styrene concentrations were greater than 50 ppm. Finally, there is also evidence concerning the influence of occupational styrene exposure on sensory nerve conduction indicating that 1) 5-10% reductions can occur after exposure at 100 ppm or more, 2) reduced peripheral nerve conduction velocity and sensory amplitude can occur after styrene exposure at 50 to 100 ppm, 3) slowed reaction time appears to begin after exposures as low as 50 ppm and 4) significant acquired loss of color discrimination (dyschromatopsia) may occur.13 Exhaust ventilation, low styrene-content resin, non-atomizing spray equipment, and personal protective equipment have historically been recommended to limit styrene vapor exposures to workers. Recent developments in specific closed molding technologies, however, may also provide protection by reducing process emissions of styrene, and, in turn, workers’ exposures.
Facility and Process Description Open Mold Plant (Plant 6) Plant 6 produced larger boats of 24 feet or more, and operated one eight-hour shift per day. The facility used an open-molding operation, a labor intensive process which required several employees to work on a single boat at the same time. Approximately 16 employees worked on the deck side, 19 worked on the hull side, and four worked on a small parts line. The small parts produced include hatch and engine covers. Three employees also worked in the gel coat spray booth. In total, approximately 72 employees worked in plant 6; this includes finishing and assembly operations as well as molding.
FRP boat components are built from the outside in. In plant 6, the first step involved the application of the gelcoat, the material that provides the color and appearance of the outer surface of the boat. Prior to each molding operation, the molds were cleaned and then a release agent was sprayed which contained a pigmented gel coat along with an initiator that formed the outside surface of the boat. The gelcoat was sprayed onto the open mold within an enclosed and ventilated booth. After gelcoating, the molds were moved to one of three laminating areas: decks, hulls, or small parts. In each of the laminating areas, a worker (gunner) applied resin and chopped glass fiber to the mold with a chopper gun.
The resins are mixed with an initiator to start a cross-linking reaction between the resin molecules. Other workers (rollers) smoothed and compressed the glass and resin using a variety of rollers and flexible blades to saturate the fibrous glass with resin and to remove entrapped air. As a result, the resin hardens to form a rigid fiber-reinforced matrix.
Depending on the part, additional layers of glass fiber and resin are added and rolled out until the desired thickness is obtained. In addition, at various stages, glass fiber mats, wood panels, and metal plates were added for additional strength.
Gelcoat Spray Booth Gelcoat was applied to the mold to provide the outer finish of the boat hull. A barrier coat was applied after the gelcoat to make hulls less permeable to moisture. Both the gelcoat and the barrier coat contained styrene as a major component. In plant 6, (see Figure 2) gelcoat was sprayed by three gelcoaters at two interconnected spray booths. A roll-up door separated the two booths. Make-up air was supplied in the two east corners of both booths and exhausted from the two west corners. When spraying large decks and hulls, the gel coaters sprayed one half of the mold, and then rotated the mold longitudinally on its stand to complete the other half. Small parts were gelcoated in the same booths. The small parts’ molds were fastened to carts and moved through the plant manually. When two colors were applied to the decks and hulls, gel coat was applied to the masked mold in the east booth. The mold was then moved to the west booth, the mask was removed, and the second color was applied. The door at the west end was frequently left open while the second color was being sprayed.
Deck Laminating Process Deck molds were moved from the spray booth located at the west end of the facility to the deck molding area. The deck molding process was operated in two parallel lines; no physical barrier separated the two lines. Molds were on wheeled supports and were moved manually with assistance of a power mule. The first coating of spray core was applied at the beginning of the line, near the exhaust hoods. Spray core is added to strengthen the part and increase thickness, while keeping the part relatively light-weight.
Additional layers of chopped glass, glass mat, wood panels, metal plates, resin and spray core were added as the mold moved down the line.
Small Parts Laminating Process Parts such as engine or hatch covers—pieces not part of the deck or hull mold—were considered small parts. Small parts molding was located in the northwest corner of the plant. These parts were constructed in a similar fashion as the decks. Molds came out of gelcoating and were moved manually on wheeled supports to the small parts area. Layers of resin, chopped glass and glass mat were added to the mold by the gunner then rolled and compressed by the rollers. Compared to the hull and deck molding processes, small parts production used much less glass and resin.