Castell Safety - Trapped Key Safety Interlocks, Lockout Tagout Equipment and Drive-away PreventionSafetyLegislation

The purpose of this document is to give outline details regarding new European Legislation and the selection of interlocks for your machinery.

If you manufacture or supply machinery of any type, the Supply of Machinery Regulations apply to you :-

Supply of Machinery (Safety) Regulations 1992 (SMR)

These regulations implement, in the U.K, the European Machinery Directive. Similar legislative controls apply in other E.C. Countries. The regulations came into force on 1st January 1993. A two year transitional arrangement was made to enable machinery manufacturers and suppliers to meet the requirements. From 1st January 1995 it is an offence to supply a new machine unless :-

• it meets the essential health and safety requirements. A detailed list of these is given in the regulations. Machines must be safe to install, operate, clean, adjust, maintain and decommission, during normal use and foreseeable misuse
• the conformity assessment procedures have been completed. This is the means by which suppliers demonstrate compliance with the regulations and involves the preparation of technical files. These will show how the essential safety requirements have been met and include risk assessment / risk reduction analysis
• it has a declaration of conformity. This is issued to the user and contains information stating the name of the manufacturer, the machine serial number / type / description and harmonised standards to which it complies. It declares conformity to the Supply of Machinery (Safety) Regulations
• it has a CE Mark affixed. This is to signify that the relevant essential health and safety requirements and requirements of other E.C. directives have been met
• it is, in fact, Safe

For some types of machinery (e.g. agri-foodstuffs, portable / hand held, woodworking and analogous materials, moulding and presses with manual feeding, etc.) special procedures are required.

Except for the requirement to have a CE mark, the regulations also include the supply of Safety Components. Castell despatch a declaration of conformity with all orders.

If you are a user of any type of machinery the Provision and Use of Work Equipment Regulations apply to you :-

Provision and Use of Work Equipment Regulations 1992 (PUWER)

These regulations implement, in the U.K, the European Use of Work Equipment Directive. They came into force on 1st January 1993. A transitional period of four years has been given. Machinery users have until 1st January 1997 to update or replace any sub- standard machinery.

"Work Equipment" is broadly defined to include any machinery, appliance, apparatus or tool. It includes assemblies of components and complete plant such as a refinery.

"Use" means any activity involving work equipment and includes starting, stopping, programming, setting, transporting, repairing, modifying, maintaining, servicing and cleaning.

The regulations give a detailed list of requirements for employers. These cover general and specific requirements. General requirements include aspects such as :-

• ensuring the suitability of the work equipment for its use
• maintenance of the work equipment
• provision of adequate information, instruction and training regarding the use of the equipment and regarding health and safety
• provision of equipment that conforms with relevant EC product safety directives

Specific requirements include aspects such as :-

• guarding and interlocking of dangerous machinery
• ensuring that work equipment is provided with a suitable means to isolate it from all of its energy sources. It is also necessary to take appropriate measures to ensure that re-connection of any energy source does not expose any person using the work equipment to any risk
• ensuring that maintenance operations are carried out safely
• ensuring protection against work equipment and articles / substances at high or very low temperatures
• ensuring protection against specific hazards. These are listed in the regulations and include, for example, any article or substance falling or being ejected from the work equipment and explosions. - provisions regarding work equipment control systems and control devices

Harmonised Standards

The Machinery Directive and the Use of Work Equipment Directive are supported by Harmonised European Standards. These standards will, as the name suggests, be applied throughout the E.C. Many of these are currently being written by CEN (Comit? Europ?en de Normalisation) technical committees. The purpose of these standards is to show how the above regulations (SMR, PUWER) can be met. In the U.K. they are published with numbers prefixed by BS EN. A document prefixed by pr EN indicates a standard that is currently in draft format and not yet completed. They are split into three basic categories :-

Type A Standards

These are fundamental safety standards giving basic concepts, principles for design and general aspects that can be applied to all machinery. For example,

• BS EN 292 Safety of Machinery--Basic Concepts, General Principles for Design. Parts I & II
• pr EN 1050 Safety of Machinery--Principles for Risk Assessment

Type B Standards

These "Group" safety standards deal with either one safety aspect or a device/ devices that can be applied across a range of machinery. Examples of subjects covered in this category include Noise, Emissions, Emergency Stops, Guarding of Machinery and Interlocks. For example,

• pr EN 1088 Safety of Machinery--Interlocking Devices associated with Guards. Principles for Design and Selection
• We are members of the CEN Committee producing this standard. It is scheduled for completion in 1996
• pr EN 954 Safety of Machinery--Safety Related Parts of Control Systems Parts I & II

Type C Standards

These form specific Machine Safety Standards giving detailed safety requirements for a particular machine or groups of machines. Examples include Food Processing Machinery, Machine Tools and Rubber Mixing Machinery. Many of these standards are currently under development.

Risk Assessment and Risk Reduction

A complete risk assessment is necessary (as described in pr EN 1050) to ascertain whether or not a machine is safe. If it is not safe then a risk reduction analysis followed by the selection of appropriate safety measures is required. A detailed list of hazards generated by machinery is given in BS EN 292-1 section 4. For example, this includes, amongst others, mechanical (crushing, shearing, entanglement, impact, etc), electrical, thermal, noise, vibration and radiation hazards. The essential safety requirements (SMR) should be met by applying the following principles in the order given :-

• eliminate or reduce risks as far as possible by inherently safe machinery design and construction
• take the necessary protection measures in relation to risks that cannot be eliminated, for example, interlocking
• inform users of any residual risks due to any shortcomings of the protection methods. Advise if any particular training is required or any personal protection equipment

Selection of Interlocks

One aspect of the risk reduction process is the selection of the correct integrity of interlocks for the machinery. The most important criteria to be considered when selecting interlocks are listed in Section 7 of pr EN 1088 :-

• the intended use of the machine (see BS EN 292-1 Section 3.12). This also takes into account conditions of use e.g.environment
• the hazards present at the machine ( see BS EN 292-1 Section 4)
• severity of the possible injury
• probability of failure of the interlock device
• stopping time and access time
• frequency of access
• duration of exposure to the hazard(s)
• performance considerations of the interlock device

When selecting interlocks "The risk to be assessed is that risk that would occur if the safety function of the interlocking device was not performed." (pr EN 1088 Section 7.2)

Upon completion of the risk assessment and risk reduction processes the correct type of interlock can then be selected to achieve the required safety. The integrity of the electrical (or pneumatic / hydraulic, etc) system into which the interlock is fitted is an important consideration. A single channel control system will rely upon the operation of a single components. If the relay / contactor was to become stuck in the CLOSED position the machine would continue to operate regardless of the status of the interlock. A single channel system is only acceptable for very low risk applications. For increased integrity and for applications of greater risk higher classifications of control systems are required. This may include, for example, dual control systems and dual control systems with cross-monitoring. (See pr EN 954-1 Safety Related Parts of Control Systems).

An interlock of suitable integrity can be used to break the machinery / motor three phase power circuit directly. This is suitable for high risk applications and is termed Power Interlocking (pr EN 1088 Section 4.1.1). Often, Power Interlocking is also the easiest way to achieve the required safety for lower risk applications.

For full information regarding machinery safety and risk assessment we recommend that you read the relevant regulations. Guidance books are also available from the Health and Safety Executive.

The following sheet describes the main areas in for which Castell Trapped Key Interlocks are particularly suitable. Please do not hesitate to contact us if you would like to discuss the interlocking of your machinery. We would be pleased to offer a free site visit by one of our Engineers, literature and details of an interlocking scheme to suit your safety requirements.

Safety of Machinery - Trapped Key Interlocking

Castell Trapped key Interlocks are used to achieve the required safety on numerous types of machinery in a complete range of industries. They are particularly suitable for :-

1. both Power Interlocking and all types of Control Circuit interlocking
2. machinery with different types of power source. e.g. pneumatic, hydraulic
3. machinery with fixed or variable run-down times
4. harsh environments. Castell have a range of material specifications and weatherproofing
5. areas requiring full-body access. If the guard swings shut during access the interlocked electrical circuit is not re-made as wiring is not required to the guards
6. full-body access within the guarded area but out of sight from the gate / control panel. In such areas persons could be accidentally trapped inside the danger area and the machinery re-started. Castell Personnel Keys can be released upon access to prevent this from happening
7. robot compounds where access must be restricted to the end of a cycle and where safe "teaching" is required from inside the guarded area
8. interlocking of mechanical devices needed to ensure safe access. e.g. "scotch pins"