Noise control in sawmilling
Sawmills are noisy environments in which to work. Damage to personal hearing, resulting in hearing loss and sometimes the discomfort of ringing in the ears (tinnitus) is likely, if suitable precautions are not taken.
Listed below are some of the main points to consider when assessing noise exposure:
- Can very noisy processes be kept physically separate from other work areas?
- Is the use of acoustic screens or barriers within a work area possible?
- Are acoustic cabins provided for operators of mechanised machinery?
- Are there suitable quiet areas or noise havens and do those exposed to high noise levels take sufficient breaks?
- Are personal hearing protectors suitable, periodically checked for wear and stored in a clean, dry place?
Experience has shown that in most sawmills the majority, and sometimes all, of the workers are exposed to daily personal noise exposures in excess of 85 dB (the upper exposure action value). Assess which machines give rise to the most noise and consider how noise emission levels can be reduced. Equally important is the need to look at the working patterns of each individual. The table below provides examples of personal noise exposures of operators of some common machines and possible improvements that can be made.
Because noise levels are still likely to remain high, even when engineering controls have been implemented, the choice of suitable hearing protectors and consideration of other necessary measures is very important. These include the following:
- marking hearing protection zones with notices;
- supervising the use of hearing protectors;
- where personal noise exposures (without taking account of hearing protectors) would remain above 85 dB, you should arrange for regular audiometry (hearing tests) of these employees to check whether your hearing protection measures are working.
Some machines, such as chippers, which emit high noise levels, require infrequent operator access. Site them in separate rooms or in acoustic enclosures.
|Machine type||Common operator exposure level without engineering controls (dB)||Common operator exposure level with engineering controls (dB)||Possible engineering controls||Personal hearing protectors likely to be required?|
|Mechanised saws, chipper canters, board separators etc||95-115||75-90||Remote control of machinery from acoustic cabin||Most of the time|
|Carriage-fed log band saws||95-100||80||Operation of carriage from acoustic cabin positioned at saw infeed||Only when leaving cabin|
|Travelling-table log band saws||100-105||It may be possible to partly enclose or shield the machine but noise reduction data is not available||Partial acoustic screening, especially at the saw outfeed||Always|
|Manually-fed re-saws||95-105||85-90||Enclosure of the machine where workpieces with at least two flat faces are normally being sawn||Most of the time|
|(Other sawmill workers)||90-105||85-95||Where noise from the major noise-emitting machinery is poorly controlled other workers will receive high noise doses from the overall noise level in the mill||Almost always|
NB Where cabins are provided or machine enclosures installed, it is very important that doors are kept shut (self-closing doors are best) and there is no damage to the fabric of the cabin or enclosure. Otherwise the noise reduction (attenuation) will be less effective.
Noise levels at many machines can be reduced by adopting proper maintenance procedures. This will often have the added benefit of lengthening the life of machine parts. For instance a well-maintained band re-saw may have an 8-10 dB difference between idling and cutting noise levels. In comparison, a poorly maintained machine may exhibit minimal difference.
Saw blade condition too can have a marked effect on noise radiation. Hammered saw blades and those containing many welds, radiate significantly more noise than well-doctored saw blades. Make sure that your saw doctor maintains saw blades correctly.
(Adapted from HSG172)