Five Ways to Compromise your Machinery Safety

1.       Use any old switch

Switches and other sensors can have welded contacts which will defeat your safety circuit. Standard switches are not designed to force separation of welded contacts.

Ensure correct selection of switches and contacts by having your safety circuit implementation validated.

2.       Don’t keep it simple

The more devices that have to operate successfully to make your machine safe the less likely it is to work reliably. If each device is treated as a lottery ticket with the win being an unsafe machine, your odds of winning increase with each additional ticket. You don’t want to win!

A well designed safety system should require reliable operation of as few devices as possible.

3.       Rely on energise-to-trip actuators with one unmonitored supply

With an energise-to-trip actuator, every protective device (fuse or circuit breaker) can defeat a safety circuit by operating correctly.

Always monitor the supply to such actuators and provide capacitor or battery backup supplies to ensure tripping on loss of supply. A much better option is to redesign the circuit to be de-energise-to-trip.

4.       Assume your pneumatics or hydraulics are perfect

Only electrical equipment goes wrong, doesn’t it? A solenoid valve never sticks, hoses never burst, pipe joints never leak and accumulators hold pressure forever.

Ensure that fluidic systems are designed to achieve the same level of reliability as the electrical systems. This may mean that redundant solenoid valves or load locking valves are required.

5.       Don’t test or maintain your safety systems

Leave your safety devices to rust solid, they’re bound to work when you need them.

Is this a gamble you want to take?

If not, ensure that you have an ongoing maintenance and testing program in place to make sure that these devices are inspected and function tested regularly so they are kept operational.

For further information on this and other matters related to Machinery Safety,  contact Mike Dean at Alberfield Risk on (08) 9221 4396 or at

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