Safety Distance Calculation
The first and by far the most important consideration is the calculation of the safety distance. There is a minimum safety mat size that should be placed between a worker and a hazardous motion. Many users will "eyeball" the application, look at the area where a machine operator would stand and say, "that looks like it needs a 24-inch wide safety mat." It may not be enough.
In standard B11.19 the American National Standards Institute ANSI) states that, "The safety mat device shall be located such that the operator cannot reach the recognized hazard before hazardous motion of the machine has ceased."
Unfortunately, the ANSI standard stops there. In order to figure out how much safety mat you need between a machine and a worker, it’s necessary to refer to the standard EN 999. This standard provides a formula for determining the correct safety mat size for a specific hazard. The formula is similar in nature to another calculation, which some readers may be familiar – the mounting distance formula for a safety light curtain.
The mat formula reads as follows:
S = (63 in./sec. x T) + (47.2 in. – 0.4H)
where:
S = The minimum distance from the danger zone to the detection zone in inches. This calculation assumes that the approach of a person toward a dangerous area is at walking speeds.
T = t1 + t2
T = The overall system stopping time.
t1 = The maximum time between the actuation of the safety mat and the controller output relays being in the de-energized state.
t2 = The response time of the machine being guarded. The time required to stop the machine or remove the risk after receiving the output signal from the safety mat system.
H = The distance above the reference plane (floor) in inches. When mats are mounted on the floor, H = 0.
