Canadian Occupational Safety

before the machine shuts down completely. "There are two zones on a camera system. If anyone comes into the fi rst zone, the machin- ery would slow down, but not stop. That sends a warning to the person that they're encroaching too close to the dangerous area. If they go further, then it would emergency-stop the equipment or stop it all together. That's what the cameras are looking for," Tucker says. Cameras systems, which are more expensive than other presence-sensing devices, replace other struc- tural guarding systems. The safety manager programs exactly which areas are danger zones and which are safe. That ability to defi ne hazardous areas more specifi cally can increase usable area and reduce pro- duction stoppages. "You can program the cameras according to how fast the movement of the machinery is and how fast a person could approach that area. That defi nes the danger zones," says Andreas Sobotta, CEO and general manager at Pilz Automation Safety Canada. "You have more freedom to program the safety area. You can have a forklift go in and out without stop- ping the process. That can all be programmed." The installation of presence-sensing devices should start with a risk assessment, Gordon says. "That way you have a clear understanding of the pro- cess, how close the operators need to get and what stopping time you need to have. If someone breaks a zone, how quickly will the machine stop? Where does the device need to be placed so that a person can't receive a residual hazard?" Safety managers should refer to CSA Z432-16 Safeguarding of Machinery and, if applicable, CSA Z142-10 Code for Power Press Operation. CSA Z432- 16 outlines a comprehensive risk analysis procedure, as well as design and operation requirements. Engi- neers use a formula to calculate minimum allowable safe distances. Plant says it's very important for workers to be trained by their employer on the limitations of presence-sensing devices. Work- ers should know how the sensors work, when the device is not func- tioning properly and what to do if a malfunction occurs. "A worker needs to be trained by the employer on: What is the sensor for? What are we trying to prevent? And how do I work safely around it?" With presence-sensing devices, workers must follow certain work practices. For example, where a light curtain is muted or blanked for a production run, operators should be trained to check the device to ensure it has been prop- erly adjusted before starting a new task. This was not done in the case of the operator who was injured using a power press brake. Most critically, Gordon says, workers must be fully aware of the hazards the devices are pro- tecting them from. They may have a false sense of security if, during AUGUST/SEPTEMBER 2017 27 object, it senses a change in pressure and sends a signal to stop, start or reverse a motor. Edges are commonly located at automatic gates, machine doors and tables, conveyors and facility doors. There are also pressure-sensitive bars: An operator leans into the bar, the sensor detects the person is too close to a hazard and shuts down the machine. The main advantage of presence-sensing over phys- ical guards is effi ciency, Plant says. For example, an operator loading pieces into a stamping machine and punching out 10 parts per hour can use a light curtain to access one particular spot in the machine. This is much more effi cient than having to remove the guard each time a piece has to go into the machine. "Or if a forklift has to come in and remove a full pallet and put in an empty one," Plant adds, "you can have a presence-sensing device shut down just the zone where the fork truck is and let the rest of the machine keep running. That's a defi nite advantage to not having to remove guarding." Moreover, Plant says, while it is hard to deceive most presence-sensing devices, a worker can remove a physical guard and leave it off permanently. There is also less need to deceive a presence-sensing device. If there's a guard in the way, the worker may want to remove it. But if the light curtain can be programmed to meet production needs, there's no need to shut the machine off, so there's less likelihood anyone will want to deceive the safety device. The main downside of presence-sensing devices, Plant says, is that they do not protect a worker from something coming out of a machine. If a hose breaks and sprays someone or a part is ejected out of the machine, a light curtain will not stop it fl ying through the beam. If you have a machine that's stamping out parts and that part could be ejected at the worker, then a light curtain is not feasible because the worker could get hurt. Another disadvantage is that presence-detecting devices don't actually prevent a person accessing the hazardous zone. They rely on there being enough time for the device to shut down the machine before a worker reaches it. A worker who puts a hand through a light curtain or walks into an area covered by a laser scanner and who reaches the hazardous part faster than the machine can shut down may be injured. "But when you have a physical guard on a machine, the worker can't get through it until they take the guard off. And if the guard is installed properly, the worker can't get it off without specialty tools. There's a lot more involved in getting into a machine," Plant says. NEW TECHNOLOGIES One new technology is the hand detection sensor, installed at the point of operation. A sensor is mounted in the corner of an opening and refl ective tape is mounted along the inside frame, creating a safety window. The device, which can sometimes be used instead of light curtains, is designed for smaller areas. Unlike light curtains, it aligns automatically and can be used in openings of various shapes. Another new presence-sensing technology is the camera vision system. Cameras are installed at roof or ceiling height, looking down on the work space. Sensors detect any intrusion, whether it's a person walking into an area or a hand or arm reaching into a danger zone. They can be programmed according to zones, providing the intruding worker with warning training, they are told the light curtain will stop if they reach their hand in. "So I start reaching closer and closer and the machine is stopping every time. But I'm counting on it being designed correctly: If I reach into an area the machine is going to stop," Gordon says. "Workers need to be told, 'This thing is protecting you from some- thing that can cut your fi ngers off.' Not to be scared of it, but to have a clear understanding not only of the safeguard but also of what it is protecting them from." Linda Johnson is a freelance journalist based in Toronto. She can be reached at lindajohnson@ sympatico.ca. LOOKING FOR A SUPPLIER OR VENDOR? Visit hrreporter.com/hr-vendors-guide 1 2 4 3 4 limitations when selecting presence-sensing devices Presence-sensing devices alone may not provide suffi cient safeguarding. Additional barrier guarding may be required to protect workers other than the operator. Presence-sensing devices must never be used to safeguard a machine with a full-revolution clutch. No attempt should be made to install a presence-sensing device until the requirements of the relevant standards have been reviewed. Presence-sensing devices are to be used during normal production only. They are not a substitute for lockout. Source: WorkSafeBC

• Cover