In this article, Hollie Dixon from leading machinery safety specialist Euchner UK highlights some of the often-overlooked aspects of machinery risk assessments.

Did you know that it is a legal requirement for every machinery manufacturer to carry out a risk assessment before anything is placed on the market? However, even when risk assessments are undertaken, they are often not of a suitable standard. Guidelines on risk assessments can be found in EN ISO 12100, a standard that describes basic risks that can occur and identifies steps with which a risk assessment can be carried out.

Content of a risk assessment

The risk assessment itself consists of the sections:

·       Risk analysis consisting of:

1.     Determination of the limitations of the machine

2.     Identification of the hazards

3.     Risk estimation

·       Risk evaluation

Risk assessment using EN ISO 12100

One of the central points of the standard is a general strategy on how to reduce the risk on a machine and here, the following three-stage process must be applied:

Step 1: The risk of injury must be reduced as far as possible by means of a suitable design. For example,  spoked wheels and pulleys can be designed with a solid infill to the prevent trapping and shearing fingers and limbs.

Step 2: If all hazards cannot be eliminated or adequately minimised with Step 1, technical measures for risk reduction must be applied where applicable. Generally, these measures involve physical guarding with control system interlocking to suit the risk/hazard involved. The safety related control functions also require an assessment to determine safety integrity. EN ISO 13849-1 gives further information on this aspect.

Step 3: Additional protective measures are the last option within the hierarchy requiring users of the equipment to protect themselves from harm through the use of PPE, training and warning signs. Unfortunately, there are too many instances where designers of equipment jump straight to this step without safeguarding or considering designing the hazard out.

This process should be well documented and included as part of the Technical Construction File (TCF) for all manufacturers of machinery and equipment covered under the Machinery Directive.

Machinery Lifecyle

EN ISO 12100 also provides guidance on which phases of the life of a machine must be considered and which of the various hazards must be assessed. These phases of life include transport, assembly and installation; commissioning; use; and dismantling, disabling and scrapping.

The erection and dismantling of a machine are included in the phases of life but often overlooked by many machine manufacturers, despite there being significant hazards during these phases, including:

·       Setting up

·       Teaching/Programming

·       Start-up and stopping the machine including emergency stopping

·       All modes of operation

·       Feeding and removal of the material from machine

·       Recovery of operation from jam or blockage

·       Restarting after unforeseen stopping

·       Fault finding/troubleshooting

·       Operator interventions

·       Cleaning and housekeeping

·       Maintenance (Preventative and corrective)

During all these tasks, hazards in the risk assessment must be taken into account and, if there is a danger, it must be reduced in accordance to the risk assessment. An additional point to the risk assessment that is frequently overlooked is the unintentional behaviour of an operator or the reasonably foreseeable misuse of a machine. Malfunctions on a machine, due to the failure of a component for example, are also to be considered.

It is not uncommon for hazards originating from a machine or installation to be missed during the risk assessment. For this reason, there are also examples for the various possible hazards in the Annex to the standard, including (but not limited to):

·       Crushing due to moving elements

·       Crushing due to lack of stability of the machine or part of the machine

·       Electrical shock or electrocution due to electrical equipment, parts of which become live under fault conditions.

·       Permanent hearing loss due to prolonged exposure to noise

·       Respiratory disease due to inhalation

·       Musculoskeletal disorders, e.g. repetitive activity

·       Burns due to contact with excessive temperatures or chemicals

Taken altogether, this can be a very complex task for the design engineer although there is wide range of external support available including training, risk assessments and safety concept design services from companies like Euchner.

Methodology for risk estimation

There are various factors that define the risk in a danger zone on a machine. Primarily, there is of course the possible extent of the harm. However, a risk is lower if the exposure to a hazard is only infrequent or brief, for example with fully automated machinery. The second factor is the frequency and duration of usage. The third factor is whether the person can avoid the hazard because, for example, the motion that causes the hazard is so slow that it is possible to leave the danger zone by simply moving away. A fourth factor is the probability of the hazard actually occurring.

In summary, EN ISO 12100 provides guidelines for the safety of machinery. It is intended to help manufacturers design safe machinery and to assist in the creation of national regulations for the safety of machinery. The standard covers a wide range of topics, including risk assessment, and is meant to help ensure the safety of machinery by reducing the risk of accidents and injuries to workers and other people who may come into contact with machinery.

As part of our feature series on safe machine design, Euchner’s Mark Staples answers some questions on the ISO 14119:2013 machinery safety standard and the procedures for the selection of a suitable interlocking or guard locking device.

What does the standard contain?

The standard describes the selection and usage of interlocking devices with/without guard locking on safety doors, safety covers and other movable safety guards. 

The term interlocking devices refers to safety switches fitted to safety doors that ensure machines/systems safely shut down on opening the door. Interlocking devices with guard locking (guard locking devices) only enable access once the risk of injury is eliminated (e.g. the hazard due to over-traveling machine movements, or machine rundown time due to inertia of moving parts, which could be something as simple as a rotating cutting blade).

The standard’s application, like all safety-related standards of this type, gives machine designers an assurance that the requirements of the Machinery directive are met.

Can it be used to obtain UKCA or CE marking?

To assign UKCA or CE marking to a machine/system, the law as applicable to machinery permits various possibilities, one of which is the use of harmonised standards. If all relevant standards are applied, ‘Presumption of Conformity’ can be assumed. 

One harmonised type B standard is ISO 14119, which is applicable independent of the machine type for the usage of safety switches on safety doors. Machine builders may find it difficult to defend themselves if applicable standards have not been followed and accidents occurred because of this.

What are an interlocking device’s component parts?

The standard defines the term “interlocking guard”, which includes the movable safety guard and the interlocking device. This generally has two parts, the actuator and position switch.

What are the guard locking principles?

ISO 14119 contains four principles of operation for guard locking devices:

1. Spring applied – Power-ON released

This is a closed-circuit current principle in relation to the function of guard locking. It means that guard locking devices are moved to the “locked” position by a spring on the removal of the power. Switching on the power opens the guard locking device.

2. Power-ON applied – Spring released

This principle operates in the opposite manner and is referred to as “electrical guard locking”. It’s an open-circuit current principle.

3. Power-ON applied – Power-ON released 

This is a principle that doesn’t change position on the removal of power. It’s also called the bistable principle. Power must be applied to change it to the other state. As the removal of power doesn’t change the position of the guard locking device, it’s considered a closed-circuit current principle.

4. Power-ON applied – Power-OFF released 

This corresponds to an open-circuit current principle as the guard locking device opens on the removal of the power. Typically used for electromagnets, e.g. on the CEM.

Which principle must be selected?

It’s possible to select from these options for the operation of the guard locking. Two of these are closed-circuit current principles where the guard locking device is closed (locked) in the event of a power failure. A guard locking device for personnel protection must use one of these two principles.

The standard permits a minor exception from this selection only if it can be shown that a closed-circuit current principle is an unsuitable method. The evidence for this will be very difficult to find. Often an open-circuit current principle is chosen for the access to the machine in the event of a power failure. However, this aspect can also be ensured using a closed-circuit current principle guard lock with an emergency release mechanism.

For process protection designers are free to decide which type of guard locking is selected as it doesn’t represent a safety function. The only requirement is that on guard locking devices for process protection, the safety of the interlocking device must not be degraded.

How must a guard locking device be controlled and how is the PL of the circuit determined?

The greatest change in ISO 14119 compared to its predecessor is the requirement to consider the control of guard locking as a safety function. This doesn’t mean that a guard locking device must always be controlled with dual channels with immediate effect, only that a risk analysis must be undertaken to determine the necessary PL. 

Guard locking devices like Euchner’s MGB function differently. These devices have a permanent power supply and the control of the guard locking is undertaken via inputs. Therefore, guard locking is not fully de-energised even on shutting down the two inputs. On these devices, the electronics contribute to the probability of failure of the control chain and a block must be added to the PL calculations.

Is the series connection of electromechanical guard locking devices safe?

Series circuits can be used without problems up to category 1. The situation becomes difficult if diagnostics on the individual safety switch is necessary. The problem here is that with a series connection, faults are masked by other safety switches. Unfortunately, this aspect is often overlooked and can lead to even relatively new equipment having guarding faults going undetected.

Euchner UK Limited has continued its recruitment drive with the appointment of Mark Tsang as a Machinery Safety Consultant. 

Commenting on the appointment, Euchner’s Managing Director (UK&I) David Dearden says: “As a TÜV NORD Certified Machine Safety Expert, Mark Tsang is a well-respected engineer and joins us with extensive knowledge and experience in machinery safety consultancy. He has an extensive portfolio of qualifications covering DSEAR, ATEX, PED and PSSR; combined with expert witness writing and 20+ years’ experience of training and mentoring in engineering consulting.”.

He goes on to say that with the introduction of new standards, the frequent amendments to legislation and the advances in safety technology, including UKCA marking and PUWER inspections, many companies choose to outsource their machinery safety services requirements. “Machine manufacturers and end users must comply with UK and European directives, as well as international standards. Euchner Safety Services can provide you with professional solutions for all aspects of machinery safety, anywhere in the world. We help machine manufacturers and users meet legal safety requirements at every stage of machine and installation life cycles.” says David.

Mark joins Euchner’s already highly-skilled team of machinery safety experts and has all the knowledge and skills required to assess the safety of machines and equipment, identify potential hazards, and offer practical advice to control or eliminate those hazards. This includes conducting risk assessments, developing safety plans and procedures, and providing guidance on compliance with relevant safety regulations and standards.

To book your safety consultation, call Euchner’s Safety Technology Centre on +44 (0)114 256 0123, email services@euchner.co.uk or click https://bit.ly/3OK32oR.

Machinery safety specialist Euchner UK Limited is continuing to strengthen its team with the appointment of Hollie Dixon in a business development role. Hollie’s roles have been product-focussed and customer-facing since joining Euchner, so she is already well-versed on the company and its portfolio of machinery safety products and training solutions. 

Commenting on the appointment, Managing Director (UK&I) David Dearden says: “Hollie’s all-encompassing role helps support our major growth plans by being a key contributor to UK sales and marketing strategies for both products and services for Euchner.

“Her role will include research and analysis of key trends in new and existing markets, collaborating with both internal and external resources on new product launches and working closely with the sales and services teams on growth strategies and the continued development of Euchner’s key accounts network.”

Industrial safety engineering specialist Euchner will use its stand at this year’s PPMA exhibition to launch two new and exciting products – the Industry 4.0 Ready CTS safety switch and CKS2 coded key system – and showcase its extensive range of guard locking products available for common fieldbus connections.

The all-new, one-fits-all CTS is Euchner’s first FlexFunction device and expands the company’s product range by sitting between the all-round CTP and specialist CTM safety switch solutions, by combining the best of both worlds in a single switch while offering maximum flexibility. A key innovation of the compact CTS – which is IO-Link compatible and Industry 4.0 ready – is the company’s new FlexFunction feature that, by using the transponder-coded actuator to determine the switch’s function, allows a single device to perform a wide variety of functions that would otherwise require several switch variants. Its compact dimensions, high locking force of 3,900N and suitability to mount in three orientations ensures the CTS is suitable for use across numerous safety engineering applications.

Combined with highly-coded, transponder-based keys, the new CKS2 from Euchner forms a safe system that meets the highest safety requirements for machine and installation lockout and starting. Thanks to the integrated evaluation electronics and depending on the key used, various safety engineering tasks are possible with the compact CKS2 key system. Additionally, combining it with Euchner’s IO-Link Gateways expands its applications and enables comprehensive diagnostic and communication functions. 

Unlike the CKS, the CKS2 can be integrated as a module within Euchner’s Multifunction Gate Box MGB2, expanding the functionality of the simple door interlocking solution to a small control terminal with access control.

Commenting, Euchner’s UK&I Country Manager David Dearden says: “The combination of MGB2 and CKS2 can be used across multiple sectors and for numerous applications to ensure process efficiency, create access rights flexibility, increase personnel and process safety, safeguard product quality and create transparency and traceability.”

The MGB2 is a unique interlocking or guard locking system for the protection of safety doors on machines and systems that, thanks to its modular approach, is more than simply a safety switch or bolt and offers a vast array of safety functionality. By incorporating additional safety modules to the MGB2, machine builders can include numerous functions, including guard locking, escape release, start/stop, emergency stop, etc. Its modular design also means the MGB2 can remove the additional need for a separate operator panel. And with networking opportunities available, it also reduces wiring and installation time. 

The MGB2, CKS2 and CTS are just three examples of the safety devices available from Euchner. For further information on these and other machinery safety solutions, the company’s technical and product support team will be on stand E68 at PPMA 2022 from 27th to 29th September.