Key Elements and Benefits of Purchasing Noise Abatement Equipment
National Laws and Standards
The first benefit of an effective ‘buy quiet’ program for the workplace is, quite simply, compliance with national regulations concerning industrial safety and hygiene.
Given the logarithmic nature of the decibel scale – every increase of 10 dBA representing a tenfold increase in sound intensity – the Worker’s Health Centre (2004, p. 1) reports that the allowable national standard over an ordinary, eight-hour working day is sustained exposure to a maximum of 85 dBA. Peak allowable noise is 140 decibels (National Occupational Health and Safety Commission, 1989), which is equivalent to a jet engine running in close proximity. Such a high noise level is clearly ‘injurious’ (see Table 1 below) and can be tolerated only for very short periods.
Table 1: Sound Intensity of Common Noise Sources (Worker’s Health Centre, 2004)
(National Occupational Health and Safety Commission, 2000).
Among the decision criteria for noise reduction in the workplace are four broad approaches:
- The ideal first step calls for reduction at the source.
- If quieter machinery and equipment cannot be had, the next critical option is to a) isolate/distance the source and, b) prevent or thwart the sound transmission path.
- Forestall exposure to noise or, if this is unavoidable, shorten sustained exposure with mandatory breaks.
- Provide and enforce use of ear protectors.
Assuming that ‘obsolete’ machines not compliant with the above standard can be gradually phased out or replaced in one go, buying decisions for the workplace could consider a broad range of options:
- Nylon or helical fibre could be used in place of the metal gears (Workers Health Centre, 2004) that transmit power, cause friction and noise in many settings. These range from the gears in a hand press, the reciprocating shaft in a mechanical loom, gears in non-electric cranes, power differentials in automotive, marine diesels, power generation and giant grinders in manufacturing.
- Should a noise survey pinpoint machinery impact as a significant source, one may choose to modify what is already in place or canvass for models that conform better to noise standards. For instance, the noise caused by the impact of push rods can be reduced in measurable terms by adjusting the pressure. Alternatively, one may look for replacement equipment where rubber, neoprene, or polyurethane pads cushion the impact of solenoid valves or air cylinders (Associates in Acoustics et. al., 2009, p. 117).
- Another source of noise is that made by parts, bottle caps, candy and other solids dropping from a conveyor and falling some height to a vibrating sorter or other metal bed. Affixing a transition slide in order to shorten “free-fall height” crn being about a 5 dBA reduction in uncontrolled noise (Associates in Acoustics et. al., 2009, p. 118).
- Great strides have been made in noise-dampened machinery. CAPS Australia (2009b) has a complete packaged solution for that ubiquitous source of noise on urban streets, the rivet hammer or pneumatic drill. The firm has achieved what it touts as the “lowest noise level in the market” (CAPS Australia, 2009b, p. 1) with a compressor built around a scroll mechanism (two scrolls, one fixed and the second rotating, make for smoother and quieter operation), sound dampers on the front cover and vibration free mounting collectively making for a noise level that approaches that of a quiet conversation, around 50 dbA.
- A final element, from the viewpoint of manufacturing process, is controlling noise at the exhaust end. Around the air effluent side of manufacturing and power generation, workers might not be directly exposed to the considerable noise of air exhaust. However, they may be subject to occasional exposure. And if not, uncontrolled noise from exhausts can reverberate throughout the plant and the surrounding community. One would therefore look for equipment that have suitable noise-dampening exhaust control already installed: exhaust, air motor, and vacuum pump mufflers, as well as breather vent, porous metal and filter silencers (CAPS Australia, 2009a).
The Humane Benefit: Mitigating Health Risks
Why does the national threshold of 85 dBA matter other than as a compliance goal for occupational health? The answer is that sustained exposure at the threshold or even below is damaging to health, productivity and social life. The National Occupational Health and Safety Commission (1989, p. 1) has even concluded that long-term exposure to noise at 75 to 85 dBA bears a small but tangible risk to some workers.
Adverse health impact surfaces as both physical and psychological damage. Physical harm is in the form of hearing loss which manifests as impaired hearing for some time after leaving work, a ringing in one’s ears, greater difficulty when conversing in a crowded bar, or being astonished when family and neighbours reprimand one for watching television at high volume.
Nor does physiological harm stop there. The sensation of ringing in one’s ears (‘tinnitus’) may be transient at first but it can worsen to a lifetime condition. Such persistent ‘buzzing’ is distracting, to say the least; the ringing can be so stressful it upsets concentration and induces insomnia (Workers Health Centre, 2004, p. 1). As with all other causes and types, such stress provokes irritability, headaches, and hypertension with all of its dire consequences for the cardiovascular system of frequently-obese Australians.
With cumulative damage to the ears, the sense of balance is upset. This can cause industrial accidents for workers who carry heavy loads from the forklift to a workstation on the production line, say, or for construction workers clambering up and down high-rise scaffolding. At the same time, noise at aggravating levels masks warnings and the sound of a wayward bucket rolling one’s way.
Beyond organic impact, the Standards Association of Australia suggests, even the hum, buzz and clatter that make up ambient noise in a modern, ‘open-plan’ office provokes a higher metabolic rate, reduces resistance to noise, and contributes to white-collar stress. Since even these can lead to gradual hearing loss, the Standards Association prefers that office environments aim for keeping background noise to no more than 40-45 dBA, roughly the same as a radio playing soft music.
Productivity suffers as colleagues at work endure miscommunication, especially in high-noise environments. Beyond the necessity of having to speak louder than normally, partial deafness afflicts high-pitched consonants first (‘S’, ‘T’, ‘K’ and ‘C’) and such sounds one takes for granted as a copier warming up, a dot matrix printer still whining away, or a strident ringing tone from one’s mobile phone (National Occupational Health and Safety Commission, 2000).
Noise, it turns out, also degrades vision. Thus, workers assembling printed circuit boards in a disastrously noisy plant may wonder why they continually have to refocus (noise causes the pupils to dilate) or why fine eye-hand coordination goes by the wayside (because clarity and colour perception worsen). Fine close work becomes difficult (Workers Health Centre, 2004, p. 1).
Requirements for a Noise-Dampening Printer Enclosure
The major requirement for the heavy-duty, floor-standing printer typical of office networked environments is, of course, the efficiency with which it dampens emitted noise. The second critical requirement is for an exhaust fan that will remove heat build-up from the laser, motors and friction caused by the paper rollers. A third key consideration comprises access panels that will permit the user to retrieve output and refill the paper tray without having to lift the entire enclosure. Finally, as a minor criterion, one might wish that such an obviously-ponderous enclosure has built-in casters so that if the network printer needs moving elsewhere, the enclosure can slide right along with it.
Online reseller Ergonomic Home Plus carries just such an ‘acoustical printer cover’ that is hyper-efficient in point of promised noise reduction: no less than 95% dampening when measured by a class 1 precision sound level meter compliant with Australian Standard AS 1259.1 (Standards Australia, n.d.) held one foot away in the horizontal and two feet in the vertical from the top edge so as to approximate distance to the ear of an average-height user.
The Canon ImageCLASS D340 All-In-One Laser Printer on which the enclosure was tested had an exposed sound level rating of 48 dBA. This dropped to 33 dBA when the enclosure was in place and all access panels closed.
Such noise-dampening efficiency relies on materials used for sound deadening. Most of the frame and opaque panels are constructed from Sonex acoustical foam sandwiched between layers of 1/2″ laminated high-density particleboard. In addition, the base board with is layered with 1/2″ vibration pad.
The sole concession to functionality is a small clear Plexiglas panel that allows the user to check if printing has started or finished. Sound leakage is minimised by employing slots for paper feed and output ejection, thus obviating the need for loose, hinged panels. There is also, of course, the obligatory cooling fan to prevent heat build-up.
Separately, Kato and Kozuka (1994) devised a three-chamber enclosure, consisting of the hollow space for the printer, a duct and a silencer channel. The latter connects the hollow space and the silencer segment so as to form a Helmholtz resonator. The Helmholtz effect relies on the fact that when sound propagation form the printer in the hollow space increases air pressure in the cavity, thence through the channel and into the duct, the resonance between the two chambers results in the main chamber having lower pressure than the outside air. Hence, air is sucked back in from the silencer cavity instead of permitting propagated sound to leak outside the enclosure.
Efficient Assessment on a Construction Site
There are three main components to undertaking the noise assessment for a construction company worksite. The first concerns choice of acoustical instrumentation. The second, related to the first, is to obtain ‘efficient’ positioning and be as close as possible to either ground-based or machine operators without interfering with their work. Lastly, one should exert best efforts to randomise or so rotate the assessment over various times during a shift, over different shifts (or day parts), and over a fortnight or so in order to obtain stable time-weighted averages (Lusk, Kerr, and Kauffman, 1998).
This assessment shall employ class 1 precision sound level meters that include the feature to measure peak noise levels and are compliant with Australian Standard AS 1259.1 (Standards Australia, n.d.).
Given that no blasting or explosions are expected in the site, the choice of microphone is limited to the random or direct incidence types.
The latter shall be employed for most of the ground-level workers since standing alongside each one requires recording sound level propagating primarily from any source the worker is facing. The wire attachment may be only two or three yards, sufficient to stand about three paces away and thus avoid interfering with work being done; at the same time, it is necessary to thrust the microphone fairly close to the ear of the worker and facing at 0 degree angle in the same direction the worker faces. There need not be a sound source directly in front of the worker being sampled. However, such a setup captures ambient sound in a non reverberant setting (Associates in Acoustics, Inc. et al., 2009).
Those ‘piloting’ tall graders and backhoes or sitting hundreds of feet up in a sky crane will need the random-incidence type of microphone. The omni-directional type, as the name implies, will give the needed advantage of recording sound propagating from any direction because heavy equipment operators are exposed to both diffuse noise and that generated by their own equipment. As dictated by occupational noise ‘best practice’ (Lusk, Kerr, and Kauffman, 1998), the microphone shall be positioned inside the operator’s cab, facing outward in the same direction as the operator. To be as unobtrusive as possible, the microphone lead should obviously be at least five metres in length so that the researcher can record sound levels off the digital dial while staying out of the way of rolling equipment.
Bibliography
Associates in Acoustics, Inc, BP International Limited & the University of Wollongong (2009) Student manual: Noise measurement and its effects.
CAPS Australia (2009a) Allied Witan mufflers and filters. Web.
CAPS Australia (2009b) Conquest Scroll Oil Free Air Compressor. Web.
Ergonomic Home + (2007) Acoustical printer covers floor models w/casters. Web.
Kato, M. & Kozuka, N. (1994) Apparatus for acoustic noise reduction of office automation devices utilizing Helmholtz resonance theory: United States Patent 5508477. Web.
Lusk, S. L., Kerr, M. J. & Kauffman. S. A. (1998) Use of hearing protection and perceptions of noise exposure and hearing loss among construction workers. American Industrial Hygiene Association Journal. 59 (7) pp. 466-470.
National Occupational Health and Safety Commission (1989) National strategy for the prevention of occupational noise-induced hearing loss [NOHSC:4004], Australian Government Publishing Service, Canberra, 1989.
National Occupational Health and Safety Commission (2000) National standard for occupational noise [NOHSC: 1007(2000)] 2nd Edition. Web.
Standards Australia, (n.d.) AS 1259.1 Acoustics – Sound Level Meters, Part 1: Non-integrating, Sydney: Standards Australia.
Workers Health Centre (2004) Noise fact sheet. Web.