IN QUEBEC, SOME 30,000 PEOPLE work in the plastics industry in about 600 plants. Accident reports of CSST (the province's occupational safety and health commission) indicate that this industry occasionally experiences incidents involving injection molding machines. The types of injuries reported range from small cuts, burns, avulsions, amputations, fractures, sprains and electric shocks to deaths. The accident reports reveal that these incidents occurred because the workers

  1. reached around, under, over or through guards into hazardous zones;

  2. removed or bypassed guards and safety devices;

  3. reached into the machine to remove stuck or jammed material;

  4. did not use lockout/tagout procedures;

  5. were victims of machine malfunctions; 6) were unfamiliar with the machine and its hazards; and

  6. operated insufficiently guarded machines.

The Injection Molding Process

Injection molding is used to produce plastic parts through a cyclic process of rapid mold filling through an injection process. Photo 1 (right) shows the small automated horizontal injection molding machine found in IRSST's machine safety laboratory. Atypical injection cycle is as follows:

  1. Melted plastic is injected, under pressure, into the cavities of a clamped mold with two parts---a moving part and a stationary part.

  2. The screw inside the heating barrel of the injection unit retracts, metering a specified amount of molten material for the next shot. In the meantime, the previous shot that is inside the mold is cooled by the cooling fluid circulating inside the mold.

  3. The injection unit retracts from the stationary platen.

  4. The clamping unit of the injection machine opens the mold.

  5. The ejector unit then forces the plastic parts out of the mold.

Figure 1 (p. 50) reveals hazardous zones associated with such a machine. The zones are numbered as follows:

  1. mold area,

  2. nozzle area,

  3. clamping mechanism area,

  4. feed opening area,

  5. ejector,

  6. heating barrel and

  7. part discharge area.

Adiscussion of hazards associated with each zone begins on p. 53. mined. The four stages of risk assessment are

  1. determine the limits and specifications of the machine;

  2. identify tasks and hazards;

  3. estimate risk; and

  4. evaluate risk.

Guidance for conducting risk assessment is detailed in ISO 14121 and ANSI B11.TR3 (Main, 2005; Roudebush, 2005; Tolbert, 2005; Paques, 2005). Risk assessment needs to be applied to industrial machines and processes to ensure worker safety. Information on incident history, energy sources, nature of the machine and affected personnel (e.g., operators, maintenance personnel, technicians, helpers, supervisors, passersby) is needed. In addition, ANSI/AIHA Z10, Occupational Health and Safety Management Systems (OHSMS), provides an effective tool for continual improvement of occupational safety and health performance. An OHSMS implemented in conformance with this standard can help organizations minimize workplace risks and reduce the occurrence and cost of occupational injuries, illnesses and fatalities. As such, five system activities described in the standard have been identified as

  1. management leadership and employee participation;

  2. planning;

  3. implementation and operation;

  4. evaluation and corrective action; and

  5. management review.

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