Noise Case Study

Case Study 6:
Noise Abatement


The following case study involves a company with operations in equipment manufacturing. The facility had 27 mechanical pump presses, 16 injection mold machines, and 7 assembly lines for boxing plastic interiors and safety switches. Products were also painted at the facility, using powder coat paint.

Hazard Identification

The hazard identified with this particular equipment manufacturing operation involved noise exposure to employees working on the assembly line. The company had a demonstrated history of one hearing shift per year. Approximately 130-150 employees worked in the assembly line area where there was borderline overexposure to noise. Employees working in the fabrication group were exposed to a time-weighted average (TWA) of 89 decibels (dBA) over 8 working hours.

Hazard Intervention

The abatement approach involved a change in the engineering controls, but more importantly, an elimination of the hazard altogether. A few engineering changes were made to the process prior to this hazard intervention such as air nozzle replacements; however they were not as effective. One year prior to the intervention, 90% of the facility was based on hearing conservation. The hearing conservation program was developed in accord with OSHA’s program. The program was intended to protect workers with considerable occupational noise exposures from hearing impairment. Once the hazard intervention was implemented the need for such a program was eliminated. Every year the company hired consultants to select company sites where they could conduct noise surveys, develop noise maps, and make recommendations to improve working conditions in the assembly line area. This particular sound level reduction project was completed in three days by the consulting group. The project focused on the assembly area with less emphasis on the fabrication area. Employees working in the assembly area were rotated and only worked a maximum of one hour per day.

Impacts of the Intervention

There were many positive health, business, and risk management results due to the implementation of the hazard abatement intervention. Health improvements resulted from the intervention because employees were not directly exposed to high noise levels. Employees were healthier, happier, and more comfortable in the workplace. Health related absenteeism reduced drastically. Employee morale increased significantly, improving the quality of the work.

The business process was improved because there were no costs associated with the hearing conservation program for the assembly line. Hearing protection, audiometric booths, and training requirements had been eliminated because the noise level was below 85 dBA in the assembly room. The costs associated with following these requirements were saved. Studies showed the fabrication area still had a few hydraulic presses that made noise after the sound levels reduction project was implemented.

The only major financial impact that resulted which affected the business process was the cost of hiring a consulting firm to assess the situation. Many positive benefits resulted from the intervention. The company was able to obtain a more accurate calculation of the true time-weighted average (TWA) for the noise exposure through noise surveys and mapping. The process used was more accurate than using noise dosimeters. Temporary employees were also eliminated from the Hearing Conservation Program. The program was reduced by 75 employees. Employees were also at a lower risk of being written up for having improper PPE. Industrial hygienists were necessary to complete an accurate survey of noise levels within the assembly areas. The company plans to conduct an IH study on sound reductions in the future.

Financial Metrics

The costs associated with time spent on managing the noise hazard by industrial hygienists and safety staff increased during the time the project was being implemented; however, once the intervention was completed the costs associated with the time spent by these individuals was greatly reduced. The noise abatement intervention resulted in a Net Present Value (NPV) of $47,249 and a NPV for future hearing loss of $198,015. The Internal Rate of Return (IRR) was 161%, while the Return on Investment (ROI) was 98%. The discounted payback period (DPP) was 0.6 years.

Lessons Learned

The economic circumstances of PPE programs support the IH hierarchy of controls. Personal protective equipment (PPE) programs that require periodic monitoring of the workplace and employee health status, as well as enforcement, equipment purchase and follow-up, are often more expensive in the long run and less effective than either engineering controls or complete hazard elimination. Management of PPE programs requires costly resources, and should be considered as a last resort in situations where other measures are not available or are in the process of installation.




Case study: Property Rights and Noise

An 81-year-old widow, Pamela Thornhill, brought legal proceedings against the scrapyard beside her home in Cambridge. She complained of noise, vibration and dust coming from the yard. Mrs Thornhill lived in the former station master's home for more 50 years. Mrs Thornhill's husband, Derek, was a railway engineer who bought the property from British Rail Engineering Ltd in the late 1960s. Derek died in 1975.

All parties agreed that the noise from the site was "sufficient to constitute a nuisance" but the scrapyard operator argued that the yard was also on former railway land. When the house had been conveyed to Derek Thornhill a clause in the conveyance restricted the house owner’s right to complain about industrial noise.

The Court had to decide whether the 1969 conveyance took away a common law right as property owners to sue for nuisance. Judge Richard Seymour said that the clause in the original land conveyance did not restrict Mr or Mrs Thornhill's right to an injunction or damages. The scrapyard was ordered to pay £25,000 damages to Mrs Thornhill. At the end of the 2009 case, the Judge said :

"The right to complain over a nuisance is not a commodity to be bought and sold on a whim."

In his view it was "not possible in law" to prevent an owner of property complaining of nuisance by the provisions in a conveyance for land.

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