OSHA 1910.217 – Requires that stop time on mechanical power presses must be checked on a regular basis and it is the responsibility of the employer to establish and follow a program of periodic inspections to their power presses to ensure that all parts, auxiliary equipment, and safeguards are in a safe operating condition and adjustment. Requires that each two hand control or safeguarding devices be located at the proper safe distance from point of operation and shall be greater than the distance determined by the following formula.
Ds = 63 inches/second × Ts;
where:
Ds = minimum safety distance (inches); 63 inches/second = hand speed constant;
and
Ts = stopping time of the press measured at approximately 90° position of crankshaft rotation (seconds).
The minimum safety distance is defined as the safety distance (Ds) from the sensing field to the point of operation or danger point where the operator could reach into the hazard.
This minimum safety distance is based on the stopping ability of the machine and a hand speed constant. When the minimum safety distance is calculated, several other factors must be taken into account, which are not included in the in the OSHA formula. These factors include the total system response time, the minimum object sensitivity of the presence sensing device, and the hand or object speed. The total system response time includes the stopping time of the machine under worse case conditions, response time of the control system, response time of the presence sensing device as stated by the manufacturer, the response time of the interface, and, if applicable, additional time allowed for the brake monitor to compensate for variations in normal stopping time. Another factor includes the penetration distance (Dpf), which is based on the light curtain’s MOS (minimum object sensitivity). The following formula is used to compute the minimum safety distance (Ds) on mechanical power presses to meet the ANSI (American National Standards Institute) B11.1 Press Safety Standard:
ANSI Minimum Safety Distance (Ds)
Ds = K x (Ts + Tc + Tr + Tbm) + Dpf
where:
K = Hand speed constant (63 inches/second)
Ts = Stop time of equipment measured at the final control element
Tc = Response time of the control system
Tr = Response time of the presence sensing device and its interface
Tbm = Additional time allowed for the brake monitor to compensate for variations in
normal stopping time
Dpf = The added distance due to the penetration depth factor (MOS). Note: If the
channel blanking feature is used on light curtains, additional safety distance
must be enforced based on the number of channels blanked.
When determining the safety distance, a portable or built-in stop-time measuring unit must be used to check the stopping time (Ts) of the machine.
Stop time measurement services provided by I. M. Services includes the following
We uses this type of device to find the stopping time of a machine before installing safeguarding devices such as a two-hand control or a presence sensing device. The stopping time measured by the STM device during the hazardous portion of the cycle is used in the OSHA or ANSI formulas to calculate the safety distance.
- Our trained technicians will perform the stop time test using the same meter as OSHA at your facility.
- Document your compliance to the above requirements.
- Make any simple adjustments needed to achieve compliance.
- Make recommendations when compliance cannot be achieved.
If your present machine control is not capable of performing a stop time measurement you should be performed on an semiannual basis in order to insure that the machine stop time has not changed. Machine maintenance, brake wear, machine alterations and other factors can extend the machine’s stopping time. If the machine stops slower than the last recordstop time, then the current safety components will need to be adjusted to continue providing the correct level of safety. For these and other reasons it is important to perform an semiannual stop time analysis.
I. M. Services provides stop time measurement service on various reciprocating “stroking/cycling” machines such as mechanical or hydraulic press and press brakes. We can also provide stop-time measurements on most machines like; four-slides, multi-slides and conveyor system.
Our trained technician will visit your facility using the same stop time measurement device as OSHA to measure the time it takes a machine to stop after a signal is given. The compiled information is then used in the OSHA and ANSI safety formulas to calculate the minimum safety distance required for the location of the machine operating controls/safeguarding device in relation to the nearest hazard.
Our stop time measurement services can also be used periodically to check the machine’s stopping time to ensure that the current safety distance corresponds to the current condition of the machine’s stopping capability. We recommend that stop time measurements be done on a regular basis, at least twice a year.
Please contact us for a pricing, scheduling or for more information.
For more information on Safety Distance: https://www.osha.gov/etools/machine-guarding/presses/safety-distance#dm