Once again, OR-OSHA has put out a high quality publication! This one is on Lockout/Tagout (LOTO) and is a MUST have for every facility. Yes I know, it only counts in Oregon, but this publication explains LOTO like none other and can be used by any workplace struggling with LOTO regardless of what state you are in. This publication EXPLAINS the myths behind “minor servicing exception”, “out of service” locks, etc. Here is a one of their explanation…
Can I use control circuit type devices such as start/stop push buttons, e-stops, selector switches, presence sensing devices, or limiting switches instead of energy-isolating devices for equipment lockout? No. These control circuit type devices do not physically isolate equipment from the equipment’s energy source. Unanticipated circumstances such as welded contacts or a loose wire shorting out can cause unexpected energization or startup. For this reason, 1910.147 explicitly rejects control circuitry in the definition of an energy-isolating device. However, under the “minor servicing” exception provided in 1910.147(a)(2)(ii), circuitry meeting the control reliability requirements of ANSI B11.19 provides the alternative safeguarding measures required under the exception. Control reliability is the capability of the control system and related interfacing to achieve a safe state in the event of a failure. For example, an interlock or e-stop having a dual channel (redundant) circuit with a self-monitoring safety module typically meets the control reliability requirements.
On the other hand, a basic start/stop circuit, used for decades and fulfilling the traditional e-stop function, is simply equipped with a single-contact button (single channel), even though it may be “safety-rated” (positive contacts). Although the probability of a single failure is low – due to the number of times the e-stop is cycled and the simplicity of the circuit – there are still several chances for a single component failing, leading to circuit failure. Because of the lack of redundancy and self-checking circuitry, this single channel e-stop circuit is not considered control reliable.
If you are considering incorporating control reliable safety control circuits, a thorough risk assessment must be done to document and verify the necessary integrity and performance levels of the control system. This ensures you are providing equivalent and effective employee protection.
Additional control circuit type device references:
- Oregon OSHA Program Directive A-156 Control of Hazardous Energy – Enforcement Policy and Inspection Procedures (Lockout/Tagout)
- ANSI B11.19 Performance Criteria for Safeguarding
- ANSI/RIA 15.06 Safety Requirements for Industrial Robots and Robot Systems
- ANSI/ASSE Z244.2 Control of Hazardous Energy – Lockout/Tagout: Alternative Methods
- ISO 13849-1 Safety of Machinery – Safety-related parts of control systems
CLICK HERE (pdf) to see all of OR-OSHA’s LOTO Guide