Engineering Controls Recommended for Water Heater Manufacturing Plant

Published October 11, 2017

At the request of the United Automobile, Aerospace and Agricultural Implement Workers of America, NIOSH has evaluated employees’ exposures to silica, welding fume, and isocyanates at a facility that manufactured water heaters. The evaluation occurred during two visits in February and July 2016, according to a health hazard evaluation report recently made available on the NIOSH website.

The facility employs nearly 1,000 production workers and has the capacity to produce 14,000 water heaters each day. Workers were potentially exposed to manganese and iron oxide from welding operations; to silica from the spray application of a silica-based enamel coating; and to methylene diphenyl diisocyanate (MDI) during injection of an insulating foam between the outer shell and inner wall of each water heater. NIOSH investigators discovered problems with ventilation in several areas. Some local exhaust ventilation units in welding areas and in the mill room were not operational, and some of the ventilated enclosures in the tank finishing department were ineffective.

In addition, some of the employees who applied insulating foam cut slits into their Tyvek suits to cool themselves. This practice potentially exposed the employees’ skin to MDI.

NIOSH’s investigation confirmed that exposures to silica and MDI represented health hazards to employees. Analysis of air samples revealed that nine of 10 employees’ exposures to silica exceeded an occupational exposure limit. Blood tests confirmed that five of 28 employees were exposed to MDI, and two employees were sensitized to MDI, placing them at higher risk for developing asthma.

None of the welding fume air samples exceeded applicable occupational exposure limits.

NIOSH recommended that the employer implement several engineering and administrative controls to reduce employees’ exposures at the facility, including developing a new system for transferring bulk silica and improving the enclosures in the tank finishing department. For more information, read the report (PDF) on the NIOSH website.