In the USA, our Occupational Safety and Health Administration (OSHA) allows for MINOR tasks that are ROUTINE, REPETITIVE, and INTEGRAL to the operation of the machinery to be done using ALTERNATIVE SAFETY MEASURES in lieu of Lockout/Tagout (LOTO). These “alternative measures” include using a safety control system (e.g., interlock). But one must read into OSHA’s Compliance Directive for LOTO to find any attempt to define requirements for these “safety systems.” Below is what employers in British Columbia have to meet when using these “alternative safety measures,” I thought it was so well written and laid out that all employers could adapt these measures to aid in their “alternative measures” for those minor servicing tasks.
emphasis added by me
What is a control system isolating device?
A control system isolating device (CSID) is a device that physically prevents the activation of a system used for controlling the operation of machinery or equipment. The system in this definition means the control system used for controlling the operation of machinery/equipment where work is being undertaken. As per the definition, a CSID operates physically to a mode or position to override or disable the control system to prevent the risk of injury to workers from the movement of the machinery/equipment or exposure to an energy source.
A switch can be an acceptable CSID if it is rated in the amperage and voltage of the circuit in which it is installed AND is capable of interrupting its rated current at the rated voltage. The switch must be used per the manufacturer’s specification and instructions (e.g., a switch rated only for a dry environment cannot be installed in a wet environment, switches used in a hazardous environment must bear the appropriate approval markings, etc.).
For machinery and a piece of equipment designed and equipped with effective energy isolating devices, the devices MUST BE LOCKED OUT before work is done on the machinery or equipment.
An electronic switch (e.g., light curtain, photo eye, and software logic generated output) is NOT considered to meet the requirements for a CSID since it does NOT physically prevent activation. IEEE Standard 100 defines a ‘physical system’ as a part of the real physical world that is directly or indirectly observed or employed.
A dual-channel safety interlock switch as a control system isolating device
A dual-channel safety interlock switch (SIS) that is:
(i) safety rated (as defined in CSA Z460-05 Control of Hazardous Energy — Lockout and other methods*),
(ii) has a direct opening action, and that
(iii) is used in the positive mode of operation
can be an acceptable CSID.
*CSA 460-05 states that safety-rated switches are tamper-resistant AND mechanically actuated devices with positively driven multiple contacts. Magnetic switches can be safety rated if they are coded and have monitored contacts.
To be acceptable, the SIS MUST be installed as part of a control system that uses safety-certified control components meeting the design architecture of ISO 13849-1 Safety of Machinery category 3 or 4. These are called control reliable control systems and are described in CSA Z432-04 Safeguarding of Machinery.
The safety-related parts of the control system (defined in ISO 13849: 2006 Safety of Machinery, referenced in Guideline G19.36(1)) MUST provide acceptable risk-reduction for the task that is being performed under its protection. An SIS installed as above is excluded from a fault of non-opening of the contact and/or non-actuation of the switch due to mechanical failure.