A Smorgasbord of Safety Topics
In anticipation of June being National Safety month, this month’s newsletter will consist of a variety of safety topics related the field of industrial control and electricity. If you need to reduce the safety risks at your facility, you may get a few good ideas. The discussion will include: what’s new in the 2018 edition of NFPA 70E, a brief introduction to ISO 13849, and a list of some common safety devices employed on the plant floor. The National Safety Council’s logo sums it up perfectly – ‘No one gets hurt!’
What’s New in NFPA70E – 2018 Edition This is the standard for electrical safety in the workplace and has seen many revisions since introduced in the 1970’s. Changes that are note-worthy follow. 1) Hazard elimination should be considered when developing work procedures. For example, you perform electrical maintenance that requires a PPE category 4 rating. In contrast to writing a procedure that includes donning the proper PPE; consider implementing a change to the circuit protective device that reduces the PPE category to a 1 or none. 2) Your safety program should require follow-up inspections of new electrical installations or changes to them. 3) Your safety program should require investigation of electrical incidents. 4) Two new steps were added to the process for Establishing and Verifying an Electrically Safe Work Condition. These steps are release stored electrical energy and release or block stored mechanical energy. 5) Informative Annex Q is new. It is titled ‘Human Performance and Workplace Electrical Safety’.
Intro to ISO 13849 Wikipedia describes this standard as follows. “ISO 13849 is a safety standard which deals with safety-related design principles of employed control system to establish different safety Performance Levels (PL).” It can be summed up by saying a risk assessment is used to determine a risk score. Based on the risk score, a defined type of control system is then required. The controls systems are rated from lowest complexity (PLa) through highest complexity (PLe). These replace the old ratings of Categories B and 1- 4. A lower-level complexity may be an old-fashion MCR relay with door guard switch. A higher-level of complexity requires input and output redundancy. Even higher levels require fail-safe systems and fool-proof designs that eliminate the possibility of incorrect operation. It is a good idea to receive training and/or qualified assistance with implementing this standard.
Common safety devices 1) Two-hand Control Relays are used for operator-attended equipment which require the operator to keep both hands on the push-buttons while the hazardous parts of the cycle are underway. The relay incorporates all the logic required for two-hand control. Go to our June 2106 newsletter for more detail on this subject. 2) Safety Light Curtain systems are used to detect that a body part (usually hand or fingers) has entered a dangerous area of a machine and then provides a signal which can be used to interrupt the machine cycle before an injury can occur. See our June 2014 newsletter for more details. 3) Safety Laser Scanners can detect that humans have walked into a dangerous area of the factory. These scanners have view distances of several meters and view ranges of approximately 270 degrees. The scanners have configuration software that enables fixed items in the view to be ignored (for example, building columns). Same as light curtains, they provide a signal to a control system to interrupt a machine or process.