Accidents on machines and systems often occur because the energy supply was not switched off properly. For this reason, both the US federal regulation 29 CFR 1910.147 and the European workplace directives require that machines and other work equipment are disconnected from the power supply and secured in such a way that the machine does not start up unexpectedly due to stored energy or that machine parts do not move unexpectedly.

Disconnecting a machine from the power supply may be sufficient in terms of safety if the disconnecting device can be seen by the person carrying out the work. However, it is crucial that no other person can reconnect the machine to the power supply. The topic of maintenance is particularly important from a safety point of view, as there are significantly more fatal accidents at work here than in production. According to the Employer's Liability Insurance Association for Wood and Metal (BGHM), 21% of such accidents occur during maintenance!

In Germany, repair and maintenance work on machinery and work equipment is subject to the requirements of the German Ordinance on Industrial Safety and Health (BetrSichV). Section 10 "Maintenance and modification of work equipment" is relevant. Paragraph 3 states that the employer must take all necessary measures to ensure that maintenance work can be carried out safely. Paragraphs 6 to 9 go on to specify: "In particular, he shall:

■ avoid hazards from moving or lifted work equipment or parts thereof and from hazardous energies or substances (No. 6).
■ Ensure that devices are available to remove energy that is still stored after the work equipment to be maintained has been disconnected from energy sources; these devices must be labeled accordingly (No. 7).
■ Establish safe working procedures for working conditions that deviate from normal conditions (No. 8).
■ Provide the necessary warnings and hazard information relating to maintenance work on the work equipment (No. 9).

Furthermore, the five basic safety rules according to DIN VDE 0105-100 for safe working on electrical systems apply in Germany:

■ disconnect;
■ Secure against reconnection;
■ Check that there is no voltage;
■ earth and short-circuit;
■ cover or isolate neighboring live parts.

The USA is more specific

The BetrSichV does not provide more specific guidelines for implementation. The situation is different in the USA: the Occupational Safety and Health Administration (OSHA), a division of the US Department of Labor, defines hazardous energies and describes how they should be dealt with.

Lockout Tagout is the systemic separation of machines and protection against restarting. The LoTo system also includes the development of procedures for machine separation and the training of machine operators.

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The US federal guideline 29 CFR 1910.147 specifically stipulates that machinery and other work equipment in special operating modes such as cleaning, maintenance and servicing must be disconnected from the power supply and secured in such a way that unexpected activation or unexpected start-up of machinery and equipment or the release of hazardous energy is excluded. The specifications are summarized there under the term Lockout Tagout - LoTo for short. Or in German: restart lockout and tagout.

Traditionally, LoTo is associated with the disconnection of electrical energy. However, all forms of energy can be dangerous, so all energy sources must be examined to determine whether the lockout/tagout should be applied. For example, energy can be stored in mechanical parts that continue to move due to inertia (such as vertical axes), capacitors, accumulators, pressurized liquids and gases, and springs.

If stored energy can cause hazards, devices for dissipating or retaining the stored energy must be integrated into the machine accordingly. Examples of such devices are resistors (for discharging electrical capacitors) or valves with corresponding line venting.

Components of LoTo: Locks and ...

On the one hand, LoTo consists of a physical barrier. This can be a main switch or an isolating device that physically prevents the transfer or release of energy - for example isolating switches, sliders, valves, barriers and blind flanges. There is also a 'personal' safety lock. In other words, a lock that is given to a person so that they can lock a main switch in the 'off' position or a valve in a fixed, closed position. Depending on the company rules, for example, all keys for a 'personal' safety lock must be kept by the person to whom the safety lock was issued or stored in a suitable place. Whether there are additional keys and who has them must be regulated within the company.

The lock ensures that the machine can only be operated after it has been properly released. It also prevents an operator from starting the machine at random. Emergency stop buttons are not part of disconnecting devices.

... mark

LoTo also includes the corresponding labeling of the disconnecting device via a sign or a tag on the lock: Why is the equipment secured against reconnection or labeled accordingly? Who approved LoTo? Who carried out LoTo? How long does the lockout last? From whom can further information be obtained?

However, LoTo is not just about fitting a lock and a sign. It is a comprehensive program that has a far-reaching impact on the company and its handling of machines. The goal is a process that ensures the safe handling of hazardous energy sources under normal operating conditions and other foreseeable conditions.

As always in the area of machine safety, the first step is an assessment of the existing machines and energy sources. Specifically, this includes the identification and assessment of risks and hazards, the identification of sources of hazardous energy, the determination of separation points and the definition of additional necessary measures (such as venting, brakes).

At the beginning of the LoTo process, it must also be determined which persons are responsible and which persons are involved in LoTo. It must be clarified which permits and approvals are required for the work. The next step is to create a LoTo process tailored to the individual needs of the company. Among other things, this describes the individual steps and responsibilities.

As a rule, an LoTo procedure consists of the following steps:

1. assessment and preparation of the task/work to be carried out on the machine;
2. handover of the equipment: the equipment (lock & tag) can be managed centrally (foreman) or decentrally (maintenance technician).
3. disconnect power and apply restart lock plus tag;
4. check point 3;
5. carrying out the task, such as maintenance;
6. authorization to release and cancel the disconnection;
7. canceling the disconnection by removing the restart interlock and the marking;
8. testing;
9. return of the equipment.

Who releases the machines again depends on the specific requirements of the company. Other elements of the process include defining the purpose, scope and rules of the LoTo procedure, describing and defining the energy control procedures to be used, and describing the means of enforcing and complying with the program.

In principle, disconnection from an energy supply must be visible (visible interruption of the energy supply circuits) or indicated by the clear position of the manual control (actuator) of the disconnecting device. Built-in devices such as pressure gauges or test points must be provided for checking the energy-free state of parts of a machine in or on which work is to be carried out. In addition, assemblies that contain hazardous stored energy and can be removed or dismantled must be provided with permanent markings warning of the hazards due to the stored energy.

Software-supported documentation

Software tools such as Pasloto from Pilz can help with the documentation of lockout-tagout processes: Among other things, this software can be used to create LoTo reports and check the company's own LoTo rules. In addition, the tool creates the poster to document the entire LoTo procedure of a plant and allows photos of the machine and energy sources to be added to the lockout tagout poster.

With appropriate software for documenting lockout tagout processes, job descriptions for handling hazardous energy sources can be easily created and documented.

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Ultimately, however, the decisive factor for success is that staff must be trained in this process. This applies to all staff, regardless of their role in the company, as all employees must understand what LoTo stands for. Authorized employees require intensive training, involved employees must be informed about LoTo and must not attempt to reconnect. Other employees must know the meaning of a lockout and employees from external companies must also be included in the training.

In short, the procedure must be implemented throughout the company. - Finally, the system must be continuously monitored and checked to ensure that it is working properly and that all elements are covered.

As a side effect, it is possible to proactively identify deficiencies and weaknesses in separation systems and implement corrective measures. Last but not least, the ability to respond to incidents and how these incidents relate to organizational changes should be determined.

To support the implementation of a LoTo system, Pilz, for example, offers a complete package consisting of two stages: lockout-tagout analysis and individual lockout-tagout procedure development.

In addition, security experts support companies in the assessment of existing LoTo programs. Although a lockout-tagout program is not mandatory under European law, this procedure can be used to meet the requirements of the BetrSichV.

Author: Niels Alpers works in Customer Support at Pilz.