Re-install the light curtains at the correct safety distance, or farther, from the nearest pinch point. Curtain horizontally between the light curtain and the press to detect a person in this zone. Mount the light curtain at the knee-to-waist height.
29 CFR 1910.217(c)(3)(iii)(e): the SAFETY DISTANCE (Ds) fromthe sensing field to the point of operation shall be greater than the distancedetermined by the following formula:
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29 CFR 1910.217(c)(3)(viii)(c): The safety distance (Dm) between thetwo-hand trip and the point of operation shall be greater than the distancedetermined by the following formula:
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The minimum safety distance is defined as the minimum distance fromthe light curtain's plane of light to the closest hazard or danger point wherethe operator could reach into the hazard.
This minimum safety distance is based on the stopping ability of the machine anda hand speed constant. When the minimum safety distance is calculated, severalother factors must be taken into account, which are not included in the in theOSHA formula. These factors include the total system response time, the minimumobject sensitivity of the presence sensing device, and the hand or object speed.The total system response time includes the stopping time of the machine underworse case conditions, response time of the control system, response time of thepresence sensing device as stated by the manufacturer, the response timeof the interface, and, if applicable, additional time allowed for the brakemonitor to compensate for variations in normal stopping time.Another factor includes the penetration distance (Dpf), which isbased on the light curtain's MOS (minimum object sensitivity).The following formula is used to compute the minimumsafety distance (Ds) on mechanical power presses to meet the ANSI(American National Standards Institute) B11.1 Press Safety Standard:
ANSI Minimum Safety Distance (Ds) |
When determining the safety distance, a portable or built-in stop-timemeasuring unit must be used to check the stopping time (Ts) of themachine.
When determining the safety distance, a portable or built-in stop-timemeasuring unit must be used to check the stopping time (Ts) of the machine. TheSTM (stop-time measurement) device measures the time it takes a machine to stopafter a signal is given. It is mainly used on reciprocating (stroking orcycling) machines, such as mechanical and hydraulic presses or press brakes.With optional accessories, it can also be used on machines that rotate, such aslathes, mills, and drills.
Industry uses this type of device to find the stopping time of a machine beforeinstalling safeguarding devices such as a two-hand control or a presence sensingdevice. The stopping time measured by the STM device during the hazardousportion of the cycle is used in the OSHA or ANSI formulas to calculate thesafety distance. The safety distance is then used to establish the location ofthe safeguarding device in relation to the nearest hazard. This device can alsobe used to periodically check the machine's stopping time to ensure that thecurrent safety distance corresponds to the current condition of the machine'sstopping ability.