Disconnecting a machine from the power supply can be sufficient from a safety point of view if the isolation device is in the line of sight of the person working on the machine. It must however not be possible for another person to reconnect the machine to the electrical grid during the work. The safety issues of servicing and maintenance are of particular concern, as considerably more fatal work accidents occur during these processes than in production. According to statements by the German Trade Association for Wood and Metal (BGHM), 21% of fatal work accidents occur during servicing.

Niels Alpers

Customer Support Pilz GmbH & Co. KG

The Occupational Safety and Health Administration (OSHA), a division of the US Department of Labour, defines hazardous energies and describes how they are to be handled. The US Regulation 29 CFR 1910.147 clearly states that machinery and other work equipment in special operating modes such as cleaning, servicing and maintenance is isolated from the energy supply and secured in such a way that an unexpected switching on or an unexpected start-up of machinery and equipment, or the release of hazardous energy, is ruled out. The specifications are summarised under the term LoTo (Lock Out Tag Out). 

Photo: Pilz GmbH & Co. KG

Taking a closer look at energy sources

Traditionally, LoTo is associated with the isolation from electrical energy. All types of energy can be hazardous, however, which is why it is necessary to check whether LoTo can be used for all energy sources. For example, energy can be stored in mechanical parts that continue to move due to inertia (such as on vertical axes), capacitors, accumulators, pressurised fluids and gases as well as in springs.

If stored energy can cause hazards, facilities for dissipating or retaining stored energy must be integrated into the machinery. Examples of this type of facilities are: Resistors (for discharging electrical capacitors) or valves with corresponding line ventilation.

Components of LoTo: Lock and…

On the one hand, LoTo comprises a physical lock. This can be a main switch or an isolation device with which the transmission or release of energy is physically prevented, e.g. isolating switches, slide switches, valves, blocks and blank flanges. There is also a “personal” security lock. Meaning a lock that is handed over 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, all keys for a “personal” security lock must, for example, be kept by the person to whom the security lock was issued or stored in a suitable place. The company must determine whether there are additional keys and who has them.

The lock ensures that the machine can only be operated after this has been properly removed again. Furthermore, the operator is prevented from being able to inadvertently start the machinery. E-STOP pushbuttons are not categorised as isolation devices.

... tag

LoTo also includes the corresponding labelling of the isolation device by means of a sign or a tag on the lock: Why is the equipment secured against restarting and labelled accordingly? Who approved LoTo? Who carried out LoTo? How long does the lockout last? Who can provide additional information? 

LoTo is not just about attaching a lock and a label. It is a comprehensive programme that has far-reaching consequences in the company and the handling of machinery. The goal is a process with which safe handling of hazardous energy sources is guaranteed under normal operating conditions and other foreseeable conditions. 

As is always the case in the field of machinery safety, the first step is an assessment of the existing machines and energies. Specifically, this includes the determination and assessment of risks and hazards, the determination of sources of hazardous energy, the determination of cut-off points and the definition of additional required measures (e.g. vents, brakes). 

Step by Step 

At the beginning of the LoTo process, it is necessary to determine which people are responsible for LoTo and which people are participating in LoTo. It is also necessary to clarify which permissions and approvals are necessary for the work. Then a LoTo process tailored to the individual needs of the company must be created. The individual steps and responsibilities etc. are described below. 

Generally, a LoTo procedure comprises the following steps: 

1. Assessment and preparation of the task/work to be performed on the machinery
2. Handover of the equipment: The equipment (lock & tag) can be managed centrally (foreman) or locally (maintenance engineer)
3. De-energise and lockout plus apply tag
4. Check point 3
5. Performance of the task, such as maintenance
6. Approval for release and cancellation of the disconnection
7. Cancellation of the disconnection by removing the lockout and the tag
8. Examination  
9. Return of the equipment

Who releases the machinery again depends on the specific process in the company. Additional components of the process include the determination of the purpose, scope and rules of the LoTo procedure, the description and determination of the energy control process to be applied and the description of the means for the implementation of and compliance with the LoTo programme. 

Lock Out Tag Out is the systematic disconnection of machinery as well as securing it against restart. The LoTo system also includes the development of procedures for machinery isolation as part of specific tasks, as well as the training of machine operators. (Photo: Pilz GmbH & Co. KG)

The 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 isolation device. Installation devices such as manometers or test points are to be provided to check whether the parts of the machinery in or on which the interventions are to be performed are de-energised.

Assemblies that contain hazardous stored energy and that can be removed or disassembled are to be permanently labelled to warn about the hazards caused by the stored energy.

Software-supported documentation

When documenting Lock Out Tag Out processes, software tools can provide support to ensure machinery can be safely de-energised: Job specifications for dealing with hazardous energy sources can be produced and documented simply. Using the PASloto software, it is possible to produce LoTo reports and check the company’s own LoTo guidelines. PASloto produces a poster that documents a plant’s entire LoTo procedure and enables images of the machinery and energy sources to be added to the Lock Out Tag Out poster. 

Employee training is essential

It is critical for success: The personnel must be trained in this procedure. This is true for all personnel, irrespective of their role in the company, as all employees must understand what LoTo stands for. Authorised employees require intensive training and any other employees involved must be informed of LoTo and must not undertake any attempts to restart the machinery. All employees must understand the significance of a lock and even employees from external contractors must be involved in the training courses. The procedure is to be implemented across the entire company.

Finally, the system must be constantly monitored and checked to ensure that it functions properly and all elements are covered. In addition, a predictive detection of defects and weaknesses of isolating systems and the implementation of corrective actions can be enabled. The ability to react in the event of incidents should also be determined, as should the relationship between these incidents and organisational changes.

The feedback from all participants on the effectiveness and usefulness of the (LoTo) process should be continuously assessed. This is then incorporated into any continuous process improvement. There will always be changes, as new machinery will be added and existing machinery changed.