Power transmission guards

The U.S. Patent and Trademark Office issued the first patent for an interlock in 1868. The interlock was a mechanical arrangement. The agency issued the first electrical interlock on a power transmission guard in 1923. In 1899, the agency issued a patent for a press guard that prevented the machine from acting if the guard was not fiiUy closed. 

Figure 13-6. Examples of power transmission guards. (From MSHA s Guide to Equipment Guarding, 1980.)...

Openings in power transmission guards, partitions, or screens must prevent people from coming into contact with hazardous elements. Such openings must comply with data in Table 13-1 and Figure 13-3. 

The earliest set of standards for machine guarding appeared in 1914. The current series of ANSI machine guarding standards (B11 series) began in 1922 with the adoption of the first standard for power presses and foot and hand presses. The first edition of the standard for guarding power transmission apparatus (B15) appeared in 1927. ... 

Safeguards include guards, devices, distance, or location. Safeguards for machines fall into two major groups mechanical power transmission safeguards, and point-of-operation safeguards. 

Mechanical power transmission equipment that is out of reach of people may not require guards. Various standards set the minimum distance required from a floor or walking surface to overhead mechanical power transmission apparatus. The minimum distance is often about 8 ft. Most people would not be likely to contact or reach above this distance. Anthropometric reach data can also establish safe distances from people to danger points. Distances to danger points within reach require guarding. There may be overhead or enclosing screens, walls or fences that create safe locations. These barriers must be permanent and substantial. Only trained workers should have access to the enclosed locations. 

Machines Power Transmission Equipment Guards in place good condition Unguarded dangers Controls - Clearly identified coded - prevent unintended activation - emergency stops near workers Power transmission items guarded Energized equipment lock-out capable ... 

The mechanical-power-transmission apparatus section covers all belts, pulleys, and conveyors that are used in industry. It describes which ones need to be guarded. For specific applications, guidance is given for preferred actions. 

Power-transmission apparatus located in basements. All mechanical power transmission apparatus located in basements, towers, and rooms used exclusively for power transmission equipment shall be guarded in accordance with this section, except that the requirements for safeguarding belts, pulleys, and shafting need not be complied with when the following requirements are met ... 

Belts, gears, shafts, pulleys, sprockets, spindles, drums, fly wheels, chains, or other reciprocating, rotating, or other moving parts or equipment shall be guarded if such parts are exposed to contact by employees, or otherwise create a hazard. Guarding shall meet the requirements of the American National Standards Institute B 15.1-1958 Rev., Safety Code for Mechanical Power Transmission Apparatus. 

Question Does a guard that is held firmly in place without the use of screws or bolts, and cannot slide out of place, or be inadvertently jostled out of place, comply with the requirement in 1910.219(m) that guards on mechanical power transmission apparatus be securely fastened ... 

General Requirements for all Machines (Guarding) and 1910.219, Mechanical Power Transmission Apparatus. 

Guarding - Mechanical power-transmission apparatus (e.g., pulleys, drives, belts)... 

Some individuals in the material handling industry argue that the improvements in conveyor safety have not kept pace with improvements in other machines and processes. Some of the noticeable improvements, however, include full enclosures of pinch points such as chain and sprocket transmissions, perimeter pull cords for emergency stops, audible alarms and a delayed start-up function, pop-out rollers, improved warning labels, and interlock guards that are designed to shut off the power if removed. 

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