Recent research has indicated that many safety upgrades are overlooking the pneumatic and hydraulic components in machinery safety control systems.
Where machinery safety is concerned, Standards like AS4024.1 Safety of Machinery (and overseas equivalents), require that all aspects of a machine's safety control system be addressed equally - electrical, electronic, pneumatic, hydraulic, mechanical etc. Unfortunately, the fluid power (hydraulic & pneumatic) components are often overlooked resulting in safety control systems with dangerously compromised integrity.
Whilst the electrical components may be cat 4 rated and installed, if they are feeding control signals to incorrectly specified pneumatic or hydraulic equipment, the whole safety control system integrity can be reduced to Cat B or Cat 1. In some cases, a great deal of effort and expense is unknowingly wasted on a "safety upgrade" that does little to improve safety.
Where risk assessment identifies the need for high-integrity safety control system components (Cat 3 or 4), it is imperative that the system integrity is not undermined by inferior components. If electrical devices are specified to be redundant/ monitored or fail-to-safe, then fluid power devices in the same system should be of the same integrity.
All too often, the onus for control system design falls to people with an electrical engineering approach who aren't properly qualified to address the fluid power or mechanical requirements of machinery safety controls. Many don't realise that quality products are available for safety-critical fluid power applications.
For more information on fluid power requirements for machinery safety, refer to AS 4024.1 (2006) or seek independant advice.