From Noise to Acoustics:
Changing the Focus for Industry
By Dave Cmar
No one disputes that the dangers of noise induced hearing loss are still present in industry today. This is especially true for businesses with older processes and limited resources to make the necessary changes to noisy machines and equipment.
Don’t lose hope, there is light at the end of the tunnel. Manufacturers that have the advantage of the latest in technology and planning, or who have religiously adhered to purchase specifications requiring quieter replacement equipment, are now reaping dividends. These include the elimination of costly hearing conservation programs and more time to focus on other issues for the EHS managers. In fact, one might expect the issue of ‘noise’ to disappear entirely from the industrial radar screen.
So far this doesn’t appear to be the case. In fact, it has shifted the focus from ‘noise’ to ‘acoustics’. Noise and acoustics are often used interchangeably by those in the profession. Traditionally, noise at industrial facilities is dealt within the context of Hearing Conservation Programs and Noise Control Programs. Acoustics, when differentiated from noise, deals with issues of perception and sound quality. Although both deal fundamentally with the same physical phenomena – ‘sound energy’, the approaches and issues surrounding each are vastly different.
Although often misapplied, guidelines for controlling industrial noise are commonly known and widely available to many engineers, health and safety professionals and industrial hygienists. The key to selecting the appropriate control measure is proper noise source identification along with knowing how employees interact with the machinery. Once these are understood, it is generally straightforward to implement process changes or investigate retrofit control measures such as enclosures, exhaust mufflers or nozzle silencers. It requires some experience to properly install these controls, but as they have been utilized extensively in industry, the pros and cons are generally understood. Controls are generally deemed successful if they reduce employee exposure below 85 dBA TWA8HR (a commonly accepted threshold for hearing loss risk – also the point at where OSHA requires Hearing Conservation Program inclusion).
In a future world where employee exposures are well below the 85 dBA TWA8HR threshold, why would noise still be a concern? And how will questions surrounding feasibility and successful implementation be answered? The driving force behind the continued focus on ‘acoustics’ is directly due to increased expectations. Increased expectations can take different forms. One interesting aspect is the shift in workplace culture to mimic Japanese style efficiency by conducting meetings on the plant floor in ‘Team Areas’ and eliminating visible barriers in both office and plant floor areas. As part of this process, many supervisors and managers have had their workspaces relocated to the plant floor and their physical offices eliminated. With the advent of mobile phone technology, many companies have eliminated landlines and two-way radios. While an environment with 80 dBA sound levels may offer a vast reduction in hearing loss risk, communicating important information either face-to-face or by telephone may be impossible in this environment. This is where the acoustics problems become more interesting.
When ‘triaging’ industrial noise, one or a few dominant noise sources are usually identified and controls applied to achieve a reduction. In addition to these primary sources there may be several secondary sources. Often these secondary sources are numerous, more difficult to control, and define the limit to which control measures can achieve. Because the focus is on reducing employee exposure, these sources could generally be ignored. These secondary sources for exposure are likely now the primary sources for communication interference and may include such things as:
- Heating Ventilation and Air Conditioning (HVAC),
- Transient Material Handling Sources,
- Conveyors and assembly lines,
- ‘Silenced’ air exhausts and blow-offs,
- Part feeders, etc.
Another aspect of ‘increased expectations’ are compliance issues. Sources that were previously masked by much noisier machine sources may now become the main source of complaints due to their impulsive or tonal nature. These may include sources such as warning sirens, buzzers, Andon Systems and other ‘nuisance’ type noises.
In addition to these ‘plant floor’ issues, similar issues continue to exist in many of the office areas where open plan designs and work privacy issues have been the bane of many office workers.
The solution to these architecturally oriented noise issues share some similarities with industrial noise problems in that the sound properties are very similar. The major difference lies in the control materials and there utilization. Because industrial noise problems seek to reduce the noise level at the receiver, the controls are oriented toward either eliminating the source or blocking the path between the source and receiver. This is true for most acoustics problems; however, when communication is involved, blocking the source path may in fact either exacerbate the problem, or in some cases, prove to be impossible.
One of the major causes of poor speech intelligibility in closed areas is excessive reflected noise or reverberation. This is almost always present in industrial facilities, however reverberant noise fields are usually negligible compared to the direct noise that receivers get from the source. Because reflective noise follows and indirect path, blocking the direct source to receiver path is not always practical, and alternatives such as adding absorption to the reflective surfaces must be considered. Optimizing a factory for intelligible communication can be an expensive and challenging task.
Controlling noise from HVAC systems is another common issue in architectural acoustics. There may be limits to what can be done if the HVAC design was not designed to meet typical office sound levels. Analyzing HVAC sources can be difficult to control because sound travels very well through duct systems in the form of both ‘stream’ noise (noise that is generated by the fans and exits through vents and diffusers) as well as ‘breakout’ noise, which is noise radiated through the duct casing. There are several controls that can be applied to HVAC systems, most common include silencers, duct lining and vibration isolation.
The most difficult part of this ‘new frontier’ for noise and acoustics is defining feasibility and successful implementation. There are some published guidelines by organizations such as ASHRAE (American Society of Heating and Refrigeration and Air-Conditioning Engineers) that provide some quantitative comparison measures. Most of these noise problems however are ‘sound quality’ issues, are very subjective, and the ‘objectionable’ threshold may vary significantly from person to person. It is crucial to define the parameters for success before implementing what could be very complex and expensive controls.
A future where sound quality eclipses health and safety may seem a long way off to companies still struggling with the cost and liability associated with maintaining their Noise Control and Hearing Conversation programs. As companies continue to invest in technology and equipment to maintain their competitiveness, the approach to acoustics and noise will continue to change and evolve. With this in mind, forward thinking companies can take the opportunity now to plan for the future. Considering the role of acoustics and communication when contemplating new facility plans, equipment layouts, ventilation systems and even information flow, can significantly enhance the way companies conduct business within their facilities. Welcome to the future!
