June is National Safety Month. It is observed every year and focuses on reducing the leading causes of injury and death at work, and in our non-work lives (on the roads, in our homes and communities). In conjunction with June being National Safety month, this newsletter will provide information on the proper use of Two-Hand Controls and some safety information about electrical power.
Two-hand Controls
Properly installed two-hand controls can reduce or eliminate the workplace injuries associated with metal-working presses, drilling/tapping operations, sheering processes, etc. These injuries include bruises, punctures, lacerations, and in worst cases – amputations. ANSI B11 and NFPA 79 are U.S. standards for applying two-hand control systems. In the NFPA 79 document, two-hand control requirements are summed up very well in section 9.2.5.6. The following information both paraphrases the section and adds pertinent information for your further understanding.
- Two-hand controls require the actuation of the two devices using both hands at the same time. While push-buttons are the commonly used device, there many new devices that do not require pushing and work by interrupting light beams or by capacitive proximity action. These devices have the added benefit of possibly reducing over-use injuries like carpal tunnel syndrome. The buttons should be placed at distances where one hand or the hand and elbow cannot successfully operate both buttons. A cover over the buttons may be a good idea to prevent tampering or accidental activations. [For ease of understanding the requirements, this article will refer to the activation devices as ‘push-buttons’.] 2. The two push-buttons must be activated within ½ second of each other by a single operator. 3. If the time limit is exceeded, both push-buttons must be released before the operation is re-initiated. To accommodate this requirement and the one above, two-hand control relays are commercially available. It is acceptable to wire your own logic schemes per the standard. 4. The push-buttons must be maintained during the hazardous parts of the process. You must not allow the operator to release the buttons and still have time to reach into the process while an injury is possible. Sometimes the push buttons are placed at a calculated distance from the hazards, such that the operator does not have time to release and move their hands into harms-way because of that distance. If this is the case, make sure that the push button distance is a fixed distance without adjustment. 5. Machine operation is stopped if the push buttons are released during the hazardous part of the process. You may need to consider drift and deceleration in the machine stopping time and consider the addition of a braking means. 6. The next machine operation is not possible until both push buttons are released. Once again, this is provided by the control scheme or two-hand control relay.
Machine designers must make reasonable efforts to prevent tampering or defeating the devices. The end-user should perform periodic checks to assure the safety feature is working according to the standard.
Electrical Myths Debunked (re-printed from ISA Niagara Frontier Section June issue of Transmitter)
Myth 2: Wood is a good insulator. Wood is a conductor, not a very good one, but still a conductor. High-voltage power has no problem moving through wood… So be careful when using wooden ladders around power lines. Myth 4: All power lines are well insulated. In fact, 90% of outside power lines are bare wires and not insulated. They may have a weather coating, but it provides no insulation or protection from electric shock. Myth 5: When a wire falls to the ground, any power going through gets automatically shut off. In most cases when a wire falls to the ground, it lands on materials that are poor conductors like snow, asphalt or a brick ledge. When this happens, the power company’s distribution system sees an increased request for electricity, not a broken circuit.