According to Pilz Australia , safety measures that are worked into the design of the manufacturing plant boost productivity. The best safety systems make work easy and lines efficient at every stage from project planning to operation and maintenance. Otherwise, safety system risks are bypassed.
Behaviour based safety (BBS) proponents cite a DuPont study suggesting that up to 96% of incidents are caused by unsafe acts. On the other hand, Australian statistics suggest that more than 90% of fatalities and injuries involving machinery and fixed plant are due, at least in part, to design. Pilz Australia believe both design and behaviour play a role in OHS.
Many administrative controls are time consuming and, when the pressure is on, are the first safety measures to be short-circuited. Injuries often occur when someone with the best intentions thinks they will quickly fix a hiccup on the line without needing to shut down the machinery.
As they feel that following the correct safety procedure slows things down and productivity suffers, the only way to make things safe is to combine maximum safety with maximum efficiency.
When safety is a part of the design, it does not compromise production or easy use, for example, guarding slapped on as an afterthought sometimes does. Pilz Australia point to controls integrated into the operation of the production line, such as programmable safety technology, as the answer.
Using programmable safety systems with safe field bus and/or software configurable safety relays that include the PNOZmulti, engineers can automate safety, so that the line watches out for the operators, provides fast access when needed, and clear diagnostics so that downtime is minimised.
Keeping safety in step with changes to manufacturing lines is also streamlined. Rather than hard wiring inputs and outputs, such digital technology allows plant engineers to design safety systems with drag and drop icon-based software, making configuration and alterations swift and low cost. Replicating the system is also simplified, as the configuration can be copied from one controller to the next.
The best safety systems also accommodate circumstances where guards must be legitimately bypassed when plant must continue to run while adjustments are made. Normally, safety gates offering access to these areas trigger a shut down of the matching zone as soon as they are opened. When these need to be suspended (not simply bypassed as often happens if the design has not catered for these circumstances) so that workers can interact with the machine in operation, a second tier of safeguards is vital.
Working on the safe suspension of safety gate operation, the system logic involves the following steps:
- Users should choose operation mode: maintenance
- Users should plug in a maintenance safety device at the segment or the door they want to open
- This device must over-ride the standard controls and be part of the appropriate safety control system
- Users should open the door at the plugged segment
- Users should use the maintenance safety device to run the machine (safe slow, limited inch and jog are common safe run modes for this application)
- If a door opens in another safety segment, the machine must stop since the maintenance person, who is operating safely, could now unwittingly injure another person who is unobserved and unprotected
There are two categories of maintenance safety devices:
- Those that constrain the user and
- Those that constrain the machine
The first group aims to keep the worker from the hazard by only operating when the user's hands are placed on the controls, such as two-hand controls and hold to run or 'dead man' switches. The second group makes the hazard avoidable and includes safe speed controls and inching timers.
Logic-based controllers, similar to the PNOZmulti, simplify the process, as operators key the requirements into speed monitoring modules and allow the software to make the computations. Each PNOZmulti can oversee the safe standstill and/or speed of up to eight drives.
The PNOZmulti is a component of programmable safety devices. Benefits for engineers include:
- Less wiring
- Installation work for fast and economical commissioning
- Troubleshooting and fault evaluation right down to I/O level
- Maximum plant availability
- For employers and employees, the outcome is a safer and productive workplace