Tips for tackling the space constraints of a legacy plant when retrofitting its safety system
Legacy plants rarely resemble the marketing photos of modern production sites, which feature wide aisles, spotless floors and high-tech operator stations. Instead, the average legacy plant is cramped and “well-used” (a euphemism for “dirty”), with harsh conditions and minimal automation – if there’s any automation at all.
The lack of automation in older production sites means that there must be significant manual interaction between operators and equipment. For instance, an operator might need to manually feed parts to machines or hold each part during a process step. Some equipment, like a drop hammer, might even be human-powered rather than machine-powered.
What challenges do safety engineers face in these situations?
The process of retrofitting safety systems in legacy plants is anything but straightforward. Safety engineers need to work around multiple suboptimal characteristics, most notably the widespread lack of automation. With the majority of tasks being performed manually, significant changes must be made to keep operators out of harm’s way.
In addition, the harsh environments of older manufacturing facilities create a need for safety devices that can maintain their functionality in the midst of oil, dust, dirt, high heat and other conditions that could hasten their breakdown. The use of non-ruggedized devices can lead to premature replacement and raise the incidence of false alarms.
Last but not least, legacy plants typically feature cramped layouts. It can be quite frustrating to install safety products within spaces that are not designed to accommodate them. Safety engineers must be mindful of the limited footprint available for their safety solutions that will, by necessity, take up a significant amount of valuable real estate.
Overcoming the constraints with standards, research and creativity
The lack of available real estate is no excuse for failing to provide a safe work environment. Fortunately, safety standards can help you determine the required placement for most safety devices. ANSI B11.19 provides a straightforward way to calculate the minimum distance from the hazard at which safety presence devices (such as light curtains and safety scanners) must be located.
Since these devices do not physically prevent an individual from reaching into a hazard zone, they need to be far enough away from hazardous machine motion that this motion will halt before an individual’s full body, hand or arm can traverse the distance from the safety presence device to the danger zone. The safety distance is calculated via the formula Ds = K(T), whereby:
- Ds = the safe distance,
- K = 63 inches per second (this is a constant), and
- T = the stopping time (in seconds) of the hazardous motion.
For example, if a safety solution involves the installation of light curtains at a point of operation for a machine that has a stopping time of 0.5 seconds (which isn’t unrealistic for an older machine), the minimum safe distance would be approximately 32 inches.
It’s also important to do your research and find safety products that can withstand harsh conditions. Numerous safety products on the market today are rated IP67 with oil resistance and high immunity to dust. There are also many different options for guarding against hazards, so it’s a good idea to investigate alternatives for tougher environments.
Be sure to get creative and work closely with your installation team. It may be necessary to fabricate custom brackets (aluminum extrusion will become your best friend). First, you’ll need to do stop time measurements and safe distance calculations. Second, do a mock-up of the factory floor to show where the safety devices will need to be installed to assess the impact on the plant floor layout.
Finally, if the impact is too great, don’t be afraid to choose interlocked hard guarding over a safety presence device. Hard guarding may not be high-tech, but it’s often the best solution. As a general rule of thumb, we don’t recommend a safety presence solution if a machine’s stop time is greater than 0.5 seconds, since the sensor’s placement could be troublesome for factory operations and operators could still come between the sensor and the danger zone.
Although it’s likely to be a more cumbersome process than working with a modern plant, upgrading the safety system of your legacy facility is still an essential undertaking that will pay off in the long run. By educating yourself on the relevant standards and researching the types of safety devices that will work well with your environment, you can keep the challenge under control.
Originally appeared on Smart Industry Forum on August 27, 2019 at https://www.smartindustry.com/articles/2019/how-am-i-supposed-to-fit-the-safety-in-there/