On February 28, 2001, the National Institute for Occupational Safety and Health (NIOSH) received a request for a health hazard evaluation (HHE) from the Saint Croix Chippewa Indian Tribe, to evaluate Universal Services Midwest (USM) employees' potential exposures during fiberglass application to the interior seams of fiberglass tanks. No health problems were reported in the request. In response, a NIOSH investigator conducted a site visit on March 14 and 15, 2001, to meet with the St. Croix tribe and the USM contract employees and observe the fiberglass laying process. Full-shift and short-term (ST) personal breathing zone (PBZ) air samples were collected for styrene and acetone. Work practices, ventilation, and personal protective equipment (PPE) use were also assessed. All of the measured full-shift and ST PBZ samples for styrene were below the NIOSH Recommended Exposure Limits (RELs) and the Occupational Safety and Health Administration (OSHA) Permissible Exposure Limits (PELs). However, one employee's time-weighted average (TWA) exposure to styrene of 43.9 parts per million (ppm) approached the NIOSH REL and OSHA voluntary PEL of 50 ppm and exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) of 20 ppm. This employee laid fiberglass inside the tank for the entire workshift. One employee's ST exposure to styrene of 92.1 ppm approached the NIOSH short-term exposure limit (STEL) and the OSHA voluntary STEL of 100 ppm and exceeded the ACGIH STEL of 40 ppm. This sample was collected for 15 minutes while the employee laid fiberglass inside the tank. All of the measured full-shift and ST PBZ samples for acetone were well below applicable exposure criteria. The highest exposures were measured for the employees who did the majority of resin and putty mixing. This employee's TWA exposure was 45.6 ppm. Gloves and eye protection were not used properly, and a need for improved use of PPE was identified. The nitrile gloves worn by contractors were not an effective barrier to prevent dermal exposure to styrene. Employees wore non-NIOSH approved filtering facepiece respirators when grinding the fiberglass seams of the tank, and no respirators were worn to protect employees from exposure to styrene. Eye protection was not worn to protect from splashing when transferring chemicals. Additionally, some chemical containers were not labeled properly. A rigorous evaluation of activities involving working in the tanks has not been conducted, and is necessary to determine appropriate safety precautions and regulatory designation as a confined space. The exhaust ventilation currently in use was not adequate in decreasing exposures to acceptable concentrations. The industrial hygiene sampling data indicate overexposure to styrene can occur at the St. Croix Aquaculture facility during fiberglass lay up. Concentrations of acetone were below relevant exposure criteria. Employees were not wearing appropriate PPE. Recommendations for ventilation and PPE to reduce exposures are given in the recommendation section of this report.