Are your safety engineering practices really safe?

Facilities must be safe in accordance with applicable laws, but do we consider the effect management style and company culture can have in a workplace, shaping employees' attitudes and behaviour towards safety? With cost and productivity pressures affecting every organisation, many employees feel pressurised into finding ‘shortcuts’ to save seconds, such as overriding door interlocks with little consideration of the consequences.

Modern safety devices, including light-curtains and scanners, can reduce the need for physical guarding but need careful consideration as they do not prevent accidentally ejected parts or materials and do require periodic inspection and testing to ensure they are working correctly. Guidance can be found in the free-to-download HSE Guidebook HSG180.

Engineering principles

Good engineering principles should be the starting point of any design or modification. However, many engineers don’t know where to find information on what good principles are or aren’t. The best place to start is with the many national and international standards that detail an engineer’s approach. An additional benefit is the presumption of conformity to the relevant legislation using designated or harmonised standards. Incorrect specification or selection of equipment is one of the biggest causes of failure/unreliability in the factory and consequences resulting from incorrect selection of a safety component could result in injury/death.

Specification Standards for safety related controls include BS EN ISO 14119-2013 and BS EN ISO 13849-1:2015. Safety interlocks are designed/installed to prevent unsafe operation/startup, e.g. when an operator requires access for cleaning. Not all interlocks are the same, e.g. the relevant standards wouldn’t suggest a washing machine door switch for a power press access panel. For door locking, there are generally three methods:

- Energise-to-Lock (Open circuit principle)

- Energise-to-Unlock (Closed circuit principle)

- Bi-stable operation (Energise to lock and unlock).

Incorrect locking is often used in machinery with residual risk, i.e. ramp-down times. Here, it would normally require an energise-to-unlock solution meaning if power is lost or the isolator switched off, doors will remain locked, preventing access to the hazard. This is documented within EN14119-2013, although unfortunately often overlooked.

Another consideration where door locking is used is the protection of others. Could someone be locked inside a manufacturing cell unnoticed? Solutions could include devices with a clear escape release being adopted, like Euchner’s CTA range of interlocks.

Interlock selection also needs careful consideration. Characteristics including operating environment, water ingress, door holding/retaining force, size, material, and electrical characteristics including coded or non-coded, solid state, electro-mechanical and RFID all make a difference to device performance and ease with which it can be overridden or manipulated.

Prevention of device manipulation

In safety engineering terms, manipulation refers to intentionally defeating a safeguard or related component by, for example:

- Removing/unscrewing components or actuator

- Using a second or incorrectly mounted actuator

- Bridging contacts.

The machinery directive considers the prevention of manipulation at design level with the operating principle in 14119:2013, which specifies how to select the correct level of coding through the actuator arrangement. This helps designers remove potential frustrations or possible motivation to defeat the safety systems, leading to safer environments for operators.

We often see guarding systems overridden by removing the actuator from the door or flap therefore actuators should be positively mounted using rivets, positively fixed by welding, or use safety screws that can only be removed using special tools. Other safeguard measures should also be considered to reduce manipulation, including strategies like hold-to-run controls or reducing machine speed if access to the dangerous zone is required.

Another area of concern is with physical guarding itself, which is often seen as an afterthought and outsourced to a local fabricator to produce and who may not consider relevant standards when designing/manufacturing guarding.

Guarding has many unknown characteristics to the general fabricator, and these can be found in relevant standards including 14120:2015 or 13857:2019. For example, simple considerations like horizontal mesh sections should always be fitted inside the guard to prevent their use as a foot grip for climbing. The standards also specify the gaps around the guarding, an often-overlooked consideration. E.g. for most applications of perimeter guarding the gap should be no greater than 180mm. In many cases, this is too big, leaving potential access for human intervention. If you can roll a football through, it’s too big!

Adequate training

Anyone working with safety systems, from design concept through to maintaining safety related aspects, must be competent. But what makes them competent? Competency is defined within many of the guidance documents but essentially it is made up from experience, formal/informal training, and knowledge.

Engineers and designers also need to keep abreast of new technologies and legislation changes. A recent example is the transition from European requirements to local regulations, e.g. UKCA. Employers have a legal duty to undertake a suitable/sufficient risk-assessment and for organisations employing five or more people, this must be well-documented. It may be beneficial to include different departments to undertake assessments and include the operators and maintenance teams too, which will ensure future safety concepts will be adopted by all.

Hollie Dixon is business development manager at Euchner

www.euchner.de