management feature | Safe working practices
there could still be several sources of noise that require hearing protection. Extruder screws rotating within the barrel do not
make much sound, but some of the related auxiliary equipment often approaches or exceeds the 85 dB limit: high-speed and high-torque gearbox lube oil pumps and main drive motor cooling blowers are notoriously loud. In many cases, engineering controls via enclo- sures are not practical. Some of the machinery surrounding the extruder
Safe operating procedures can minimize worker exposure to increased risk when performing tasks requiring the removal of machine guarding – for example, operating procedures specify the wearing of a full face shield for cleaning out vacuum vents. Photo courtesy of PolyTech
slide-plate screen-changer. This equipment is inher- ently safe as long as the equipment is in continuous operation. It is the periodic screen-change that creates a situation where operators are exposed to a higher risk for a short period of time – in this case, to remove the fouled screen and replace it with a clean one. During this time, the machine guards need to be opened for access to the screens. This is where work practice controls take over from the engineering controls to minimize exposure. Proper training of operating staff, for example, should include an awareness of the risks involved when performing this task. Minimizing the risk of exposure to accidental release of pressure, in this example, would require persons performing the screen change to wear a full-face shield as part of the procedure for an additional level of protection. Similar heightened risk is also associated with the
Personal
protective equipment should be
provided when work practice
controls are not sufficient
manual cleaning out of vacuum ports, another task that must be performed when the machine is operating – the task is usually required as a result of an upset condition or could also be performed at some regular frequency. In this example, the task requires the removal of two levels of machine guarding – the vent port cover and fume extraction system. Therefore, there should be specific procedures for safely accessing the open vent. Operating procedures would require persons cleaning the vent to wear a full-face shield and possibly a respirator.
Sound – engineering controls for noise are accomplished with sound enclosures designed to keep environmental limits to less than 85 decibels (eight-hour, time-weighted average). However,
48 COMPOUNDING WORLD | November 2013
www.compoundingworld.com
often exceeds the 85 dB limit: strand pelletizers, vacuum conveying blowers, pellet classifiers, centrifu- gal spin dryers and so on. Work practice controls must then specify the wearing of proper hearing protection for safe operation of extrusion machinery.
Smell – when plastic resins are melted and heated to their processing temperatures, potentially harmful fumes and vapours are generated in the process. The specific volatiles that are generated are related to the raw materials and must be contained through a well designed fume extraction system. When entering the compounding area, a strong odour is a clear sign of inadequate engineering controls; requiring operating staff to wear respirators is not an acceptable solution.
Taste – aside from any specific PPE required for safe handling of noxious chemicals and raw materials (as specified in MSDS sheets), fugitive dust is an environ- mental hazard associated with most compounding applications. In the case of materials with known dust explosion potential, engineering controls are mandated by national electrical codes and insurance underwrit- ers. The problem is with more common materials that are not required by law to have such controls to be in place. As described previously for fumes and vapours, simply requiring operating staff to wear dust masks is not an acceptable solution.
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