Guard all pinch points and ensure

correct programming of STOP buttons

Worker dies when head is crushed in pinch point

In a fatal accident in a plywood mill, a worker was crushed between the plywood press charger and the charger frame. The hazards involved an unguarded pinch point and incorrect programming of the programmable control system STOP button.

This bulletin explains what happened in the plywood mill and what steps were taken to control the hazards. This fatal incident could have happened in other types of manufacturing plants where there are large pieces of machinery moving goods along in a line process. Even if the machinery in your industry is different, you can apply the lessons from this incident to your own workplace. Look for places where pinch points are not guarded and where the STOP button is not wired or programmed in a fail-safe way.

The elevated work platform is not shown in this simplified drawing. The STOP button was actually attached to the work platform and moved up and down with it.

Charger/press system in plywood mills

In a plywood mill logs are fed into a lathe. The lathe rotates the log, peeling thin layers of wood called veneer off the log. Veneer is cut into either sheets or random-size pieces, depending on the quality. Sheets are used for the face and back of the plywood, while the random sizes are used in the middle of the panel. The layers of wood have glue in between them - the more layers, the thicker the plywood. The veneer panel is fed into the hot press and pressed using both pressure and temperature to cure the glue. Once the glue is cured, the edges of the panel are cut off to create a plywood panel, usually 4 ft. by 8 ft. in size.

The process involves workers working with large pieces of machinery that move the pieces of wood through the process. Some mills have more machinery than others, but all plywood mills have a press charger and plywood press. Veneer panels are loaded into the press charger, which moves these panels into the press in large batches.

At this plywood mill, the press charger and plywood press are linked together so that when the charger moves forward to feed the panels into the press it creates a pinch point. This is a place where a worker could get injured if any body part is in the way of the stacked, moving tray of panels as the press charger completes the loading process. (Other mills may have different types of charger/press systems and different pinch points.)

What was this worker's job?

The worker who died was working as a press helper. At this plywood mill, a press operator and a press helper work together on this plywood press. The press operator stands at the front of the press charger and loads the wood panels into it from the top to the bottom. The press helper straightens out the panels as they are loaded, working from top to bottom to ensure they are aligned properly. The press operator and the press helper use two separate elevated work platforms to travel from top to bottom. The usual procedure is for the press helper to engage the STOP button on the elevated work platform when aligning the panels, and then disengage the STOP button when the alignment is completed.

Once the panels are aligned, the press helper moves to the charger control panel and presses the START CYCLE button to activate the press charger. Before the cycle starts to load panels into the press, the pinch point gap is about 33 cm (13 inches) wide. The gap narrows to zero as the panels are moved from the press charger into the press.

The pinch point gets smaller as the press charger advances.

How did the press helper get crushed in the pinch point?

In this plywood mill, the pinch point between the press charger and the charger frame was not guarded and the STOP button for the charger was programmed incorrectly.

On the day of the incident, it is suspected the sequence of events took place as follows:

• The STOP button on the elevated work platform was engaged while the press helper was aligning the panels.
• The press helper completed the alignment process and then moved away from the pinch point but forgot to disengage the STOP button on the work platform.
• The press helper went to the charger control panel - located 2.1 metres (7 feet) away from the pinch point - and pushed the START CYCLE button but nothing happened. The press helper, realizing that the STOP button on the work platform had not been disengaged, went over to the work platform and disengaged the STOP button.
• As soon as the STOP button was disengaged, the press charger began to cycle. There was a 2.9 second delay as the squaring arms "squared" the load before the press charger started moving forward. In that time the press helper either fell into the pinch point, or, not realizing the press charger had started the cycle, tried to straighten out panels near the bottom.

Why did the accident happen?

The pinch point between the press charger and the charger frame is a hazard. The risk to workers was not adequately controlled in this plywood mill.

• The space was large enough to enter and was not guarded well enough, allowing a worker to access the space and become crushed when the charger advanced.
• The STOP button on the elevated work platform was programmed incorrectly, allowing the press charger cycle to start or continue when the worker disengaged the STOP button.

Controlling risks

The best approach to controlling risk is to follow this order:

1. Eliminate the hazard (the pinch point).
2. Install engineering controls to reduce the risk (such as guards and safety switches).
3. Use administrative controls such as training and written safe work procedures (such as using lockout and replacing guards before activating machinery). Administrative controls can only reduce the risk of workers being caught in a pinch point; they do not eliminate it. Keep in mind that workers can inadvertently forget to follow a safe work procedure if they are distracted or encounter something unusual.
4. Personal protective equipment (PPE) such as hard hats and safety boots may reduce the risk to workers from some hazards, but with large moving pieces of machinery, PPE is ineffective.

Hazards and control measures

This fatal accident showed that there were two hazards that could be found in many workplaces: unguarded pinch points and incorrectly programmed STOP buttons.

Unguarded pinch points

The best way to control risk is to eliminate the hazard. In some operations employers can eliminate the pinch point altogether by changing the design of the equipment. By using instructions, guards, signs, and training, employers do not eliminate the risk of the worker being caught between moving parts of machinery, they can only reduce the risk.

If it is impossible to eliminate the pinch point, a guard preventing entry is an effective way of reducing the risk of a worker being caught in a pinch point. In addition, the risk will be further reduced by placing safety switches that render the machinery inoperable if the guard is removed. Using the guard and safety switches will help prevent serious injury and death.

After the fatal accident, this plywood mill installed a guard so that no one could inadvertently fall or put any body part into the pinch point. In addition, when the top half of this door is opened, it causes the machinery to shut down. The bottom half acts as a guardrail to the elevated work platform and can't be opened unless the top half is open (which means that the machinery has already shut down before the bottom half can be opened).

Safety devices must be inspected and maintained regularly to make sure they are working properly.

Incorrectly programmed STOP buttons

STOP buttons should not activate machinery. Examine your workplace to determine whether or not any of your local STOP/START buttons or emergency stops are set up in the same way they were in this plywood mill. Look for switches that are "relayed"- that is, look for switches in sequence that will power up the machinery.

Pay particular attention to the STOP button near the machinery. If the STOP button can also be used as a START button to activate the machinery, change the configuration. Make sure the sequence will protect workers when machinery is started. The correct start-up sequence will ensure workers are a clear distance away from a pinch point as the cycle starts.

Suitable control measures

In summary, to control the hazards of pinch points:

• Guard all pinch points on machinery against inadvertent or deliberate worker access.
• Install a safety switch on the guard so that if the guard is removed, the safety switch will deactivate local machinery. Install a second switch as a back-up switch (for redundancy). No buttons should be able to start the machinery while the guard is removed.
• The START CYCLE button to activate machinery should be located on a control panel a safe distance from all pinch points.

Specific recommendations for this type of charger/press system

If your workplace has a system similar to the one in this plywood mill, these specific recommendations may be helpful:

1. The START CYCLE button on the press charger control panel is located a safe distance away from any pinch point. Depressing this button is the only way the cycle will begin.
2. The only way the press charger will restart after any safety switches have been activated is after two things happen in succession:
(a) The guard has been put back into place, allowing reconnection of the safety switches so electrical current flows for machine startup, and
(b) The START CYCLE button (located a distance away from the pinch point at the press charger control panel) is depressed by a worker.
3. The pinch point is guarded in such a way that the machine guard must be opened to make any adjustment within the pinch point area.
4. Two safety switches are installed on the guard (one is a back-up switch), both of which shut down the machinery any time any portion of the guard is removed.
5. The guard is configured so that no body part can access the pinch point with the guard in place.
6. When an elevated work platform provides access to the panels, the guard (with required safety switches) is attached to the work platform. A two-tiered guard, divided between an upper half and a lower half, allows the bottom half of the guard to act as a guardrail when the top half is open.
7. Program the programmable control system to prevent a cycle from occurring until manually restarted if an expected event has not occurred within an assigned time.
8. In case a worker is ever caught in the machinery, it must be configured to prevent further harm to the worker when they are being extracted.
9. Make sure that all areas adjacent to the pinch point area (such as walkways and platforms) are free of tripping hazards.
10. Provide workers with written safe work procedures at all times and train them to follow these procedures at all times, for example, making sure that all workers are clear of any pinch points before starting up machinery.
11. Ensure supervisors enforce the use of safe work procedures.
12. Review the engineering controls and safe work practices on an ongoing basis to ensure they are adequate.