When noise exposures persist as a problem
May 8, 2009
Located in Chattanooga, Tenn., Dixie Industries, a division of Columbus- McKinnon’s Rigging Group, faced some serious noise challenges. At the heart of Dixie Industries’ operation is the forging of various steels, including carbon, alloy and stainless. Forging is one of the loudest of all manufacturing processes, involving the use of heavy-duty hammers, presses and rollers to generate forces upwards of 50,000 tons.
In the forging process, operators stand in front of hammers that cycle up to 80 strokes per minute. The combined mass of the top ram and dies often exceeds 6,000 lbs. and generates a massive amount of kinetic energy. Most of this energy is transferred in the deformation of the steel, but as the steel reaches its desired geometry, the excess energy is converted into sound. Typical employee noise exposure levels reach upward of 108 to 112 dBA.
Dixie Industries’ hearing conservation program required all workers to wear hearing protection throughout the facility and to use dual protection in the forge area where exposures average 110 dBA throughout the workday (a 10-hour time-weighted average, or TWA). The Noise Reduction Rating (NRR) of earplugs was de-rated using the “subtract 7, divide by 2” method, with 5 dB added to that value to estimate attenuation of the dual protection.
According to Dixie Industries’ production manager, Ed Tougaw, this mid-sized forging operation found itself caught in a vicious cycle. For more than a decade, the operation had implemented more than 30 different noise-reduction projects and spent more than $1 million to install baffles, insulation walls and noise-absorbent materials; redesign air valve controls on hammers; install quieter auxiliary equipment; relocate non-forging employees away from extreme noise areas; and purchase less noisy equipment (“buy quiet”).1
The noise problem persisted, and in the fall of 2005, Dixie Industries was cited by Tennessee OSHA [TOSHA] for excessive noise exposures. TOSHA instructed Dixie Industries to develop a detailed plan for further engineering or administrative controls to minimize noise exposures. But according to Tougaw, even with these additional engineering controls, the company did not gain anything on hammer operators’ direct exposure and the overall noise was reduced by only a couple decibels in the area of reflected and indirect exposure.
A “science fair” presentation
Tougaw turned to Dr. Kevin Michael and Dr. J. Alton Burks, who had recently introduced in-ear dosimetry technology at another steel processing plant. After receiving approval from management, he and his team presented a two-step plan to TOSHA. “We referred to it as our ‘science fair’ presentation,” he said. “We covered the conference room walls with photographs of our previous engineering work consisting of 30 projects carried out over 11 years and representing an investment of $1.8 million. We included proof of our administrative controls, including daily audits of our double hearing-protection policy and proof (in the form of disciplinary action) that we were enforcing it.”
“The final element,” Tougaw continued, “was a proposal to use a different method to determine our actual exposure levels. We were fortunate that the representatives from TOSHA were aware of the technology and open to the proposal. They gave it their blessing and we kicked it off.”
“We decided to use in-ear dosimetry to collect actual exposure data and not use it as a replacement for our existing hearing conservation program,” Tougaw explained. A team was trained for the program, consisting of the plant’s environmental engineer, production supervisor, production manager and two hammer operators. Six workers were monitored full-time, and they recorded their daily in-ear measurements over several months. Concurrent, ambient noise measurements were also recorded with a Type II sound level meter.
The team collected and analyzed data from both in-ear and ambient dosimetry, with noticeable results. Workers utilizing in-ear dosimetry experienced noise exposures under the 90 dBA PEL. In fact, nearly all measurements were under 80 dBA (Table 1). Compared to ambient personal dosimetry, the workers exposed to the loudest noise achieved only 25 percent of their daily dose. The protection was working.
In-ear dosimetry was able to determine that with proper protection, training and motivation, workers could be adequately protected from extreme noise over an entire work shift. “Our extensive field studies showed workers were adequately protected, especially since they were wearing double protection,” said Dr. Michael. “In fact, nearly all industrial exposures can be reduced to a safe level with a properly-fitted, single hearing protector. This demonstrates that conventional de-ratings can be grossly inaccurate.”
The data was presented to TOSHA in April 2007 and the citation was abated two months later. Dixie Industries continues to use in-ear dosimetry in its hearing conservation program. The noise dose of its hammer operators is monitored on an annual basis. According to Tougaw, “the success of this alternative program sent a message that everyone could and should make a contribution to the overall safety environment at Dixie.”
1 “Establishing the Real-World Adequacy of Personal Hearing Protection in a High-Noise Environment: A Case Study in a Forging Operation,” presented by Kevin Michael, Ph.D., at the 2008 American Industrial Hygiene Conference and Expo.