29 CFR 1910.217(c)(3)(iii)(e): the SAFETY DISTANCE (Ds) from
the sensing field to the point of operation shall be greater than the distance
determined by the following formula:
| Safety Distance
(Ds)
|
| |
Ds = 63 inches/second x
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). |
|
29 CFR 1910.217(c)(3)(viii)(c): The safety distance (Dm) between the
two-hand trip and the point of operation shall be greater than the distance
determined by the following formula:
| Safety Distance(Dm) |
Dm = 63 inches / second x Tm
where:
|
Dm = minimum safety distance (inches):
|
63 inches / second = hand speed constant; and
|
|
Tm = die closure after it has been tripped (seconds). For full
revolution clutch presses
with only one engaging
point, Tm is equal to the time necessary for one and
one-half revolutions of
the crankshaft. For full revolution clutch presses with more than
one engaging point, Tm shall
be calculated as follows: |
| |
|
[ |
|
1 |
] |
x |
time necessary to complete one revolution of the crankshaft (seconds) |
| Tm |
= |
1/2 + |
|
|
|
|
|
Number of engaging points per revolution |
|
|
| Safety
Distance Chart |
|
|
|
|
.055 |
|
-- |
|
3½" |
|
.317 |
-- |
|
20" |
|
.063 |
|
-- |
|
4" |
|
.325 |
-- |
|
20½" |
|
.072 |
|
-- |
|
4½" |
|
.333 |
-- |
|
21" |
|
.079 |
|
-- |
|
5' |
|
.341 |
-- |
|
21½" |
|
.087 |
|
-- |
|
5½" |
|
.349 |
-- |
|
22" |
|
.095 |
|
-- |
|
6" |
|
.357 |
-- |
|
22½" |
|
.103 |
|
-- |
|
6½" |
|
.365 |
-- |
|
23" |
|
.111 |
|
-- |
|
7" |
|
.373 |
-- |
|
23½" |
|
.119 |
|
-- |
|
7½" |
|
.380 |
-- |
|
24" |
|
.126 |
|
-- |
|
8" |
|
.388 |
-- |
|
24½" |
|
.134 |
|
-- |
|
8½" |
|
.396 |
-- |
|
25" |
|
.142 |
|
-- |
|
9" |
|
.404 |
-- |
|
25½" |
|
.150 |
|
-- |
|
9½" |
|
.412 |
-- |
|
26" |
|
.158 |
|
-- |
|
10" |
|
.420 |
-- |
|
26½" |
|
.166 |
|
-- |
|
10½" |
|
.428 |
-- |
|
27" |
|
.174 |
|
-- |
|
11" |
|
.436 |
-- |
|
27½" |
|
.182 |
|
-- |
|
11½" |
|
.444 |
-- |
|
28" |
|
.190 |
|
-- |
|
12" |
|
.452 |
-- |
|
28½" |
|
.198 |
|
-- |
|
12½" |
|
.460 |
-- |
|
29" |
|
.206 |
|
-- |
|
13" |
|
.468 |
-- |
|
29½" |
|
.214 |
|
-- |
|
13½" |
|
.476 |
-- |
|
30" |
|
.222 |
|
-- |
|
14" |
|
.484 |
-- |
|
30½" |
|
.230 |
|
-- |
|
14½" |
|
.492 |
-- |
|
31" |
|
.238 |
|
-- |
|
15" |
|
.500 |
-- |
|
31½" |
|
.246 |
|
-- |
|
15½" |
|
.507 |
-- |
|
32" |
|
.253 |
|
-- |
|
16" |
|
.515 |
-- |
|
32½" |
|
.261 |
|
-- |
|
16½" |
|
.523 |
-- |
|
33" |
|
.269 |
|
-- |
|
17" |
|
.531 |
-- |
|
33½" |
|
.277 |
|
-- |
|
17½" |
|
.539 |
-- |
|
34" |
|
.285 |
|
-- |
|
18" |
|
.547 |
-- |
|
34½" |
|
.293 |
|
-- |
|
18½" |
|
.555 |
-- |
|
35" |
|
.301 |
|
-- |
|
19" |
|
.563 |
-- |
|
35½" |
|
.309 |
|
-- |
|
19½" |
|
.571 |
-- |
|
36" |
|
The minimum safety distance is defined as the minimum distance from
the light curtain's plane of light to the closest hazard 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 Device
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. The
STM (stop-time measurement) device measures the time it takes a machine to stop
after a signal is given. It is mainly used on reciprocating (stroking or
cycling) machines, such as mechanical and hydraulic presses or press brakes.
With optional accessories, it can also be used on machines that rotate, such as
lathes, mills, and drills.
Industry 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. The safety distance is then used to establish the location of
the safeguarding device in relation to the nearest hazard. This device can also
be used to periodically check the machine's stopping time to ensure that the
current safety distance corresponds to the current condition of the machine's
stopping ability.
|
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