NIOSH Recommends Controls to Reduce Noise Exposures at a Foundry

Cutoff saw operators’ noise exposures at an unleaded brass foundry were “well above” both NIOSH and OSHA occupational exposure limits, NIOSH staff found during a health hazard evaluation (HHE) of the workplace. Facility management requested that the agency examine noise exposures, evaluate the effectiveness of workers’ hearing protection, and identify noise controls for the foundry, which cast and manufactured lead-free brass plumbing and flow-control valves. The cutoff saw operators worked in an area containing four saws, and their noise exposures stemmed from several activities. For example, finished castings were transferred from the foundry to a rotating table in the cutoff area via a barrel shaker, and workers placed castings onto a metal cutting deck, pushed them into the abrasive cutoff saw blades, and dropped or tossed valves into a metal bin for finishing. Each saw had a 20-inch diamond abrasive cutting blade that operators used to separate valves from excess metal from the casting process.

NIOSH’s HHE report states that workers’ full-shift time-weighted average (TWA) noise exposures ranged from 112 to 116 decibels, A-weighted (dBA), based on NIOSH noise measurement criteria. Using OSHA’s noise measurement criteria, exposures ranged from 107 to 114 dBA. Foundry employees worked 10-hour shifts, so the NIOSH recommended exposure limit and OSHA action level, both of which are 85 dBA for an eight-hour shift, were reduced to 84 dBA and 83.4 dBA, respectively. OSHA’s permissible exposure limit for noise is 90 dBA, and the NIOSH report notes that the PEL is not adjusted for extended work shifts.

“TWA noise exposures were well above 100 dBA,” the report states. “At 100 dBA, NIOSH recommends, and OSHA requires, employees to use dual hearing protection, that is, wearing both ear plugs and earmuffs.”

NIOSH staff conducted hearing protector fit testing for six saw operators. Agency personnel found that the workers’ foam-insert ear plugs reduced noise by 15 to 31 decibels, and custom-made ear plugs reduced noise by 18 to 28 decibels, meaning that the ear plugs would not always keep operators’ exposures below relevant occupational exposure limits. During the evaluation, NIOSH staff observed that some workers did not properly wear earmuffs and did not fully insert their ear plugs into their ears, reducing the effectiveness of the hearing protection.

In addition to ensuring that the operators wear their hearing protection properly and continuing to include them in a hearing loss prevention program, NIOSH identified several potential engineering and administrative controls to help reduce noise exposures. The agency’s report recommends reducing saw noise using blade stiffeners, dampeners, and stabilizers; optimizing the rotational speed of the saw blades; and keeping blades sharp. Other engineering controls include adding an ultra-high-molecular-weight polyethylene plastic layer to the cutting deck to eliminate metal-to-metal contact between the cutting deck and the castings, and considering sound-absorbing or vibration-reduction treatments for the cutoff saw enclosures. Administrative controls such as using a job rotation schedule or a “Buy Quiet” program, which involves installing or replacing equipment with options that generate less noise and vibration, can also help reduce noise exposure.

To learn more, download the HHE report (PDF) from the NIOSH website.