Hesi Safety srl

• UNI EN ISO 13855:2010  Safety of machinery -- Positioning of safeguards with respect to the approach speeds of parts of the human body
  

The safety distance "S" is the minimum distance between a photoelectric barrier and a hazard zone.
The safety distance prevents somebody from reaching the dangerous parts of the machine before its movement is stopped.
UNI EN ISO 13855/EN 999 specifies a formula to calculate this distance.

The synthetic formula described in that standard is:

S = K x T   + C                                       

Where:

• S = minimum safety distance between the safeguard and the hazard point, expressed in mm.
  

• K = approaching speed of the body or the limb, expressed in mm per second.
  

• T = total time needed to halt the machine, composed by:
  

• t1 response time of the safeguard device, in seconds
  

• t2 time needed by the machine to halt, in seconds
  

• C = additional distance in mm, that takes in consideration the possible approach of the body to the hazard zone before the safeguard device has been activated.
  

          




















Evaluation of the safety distance for the vertical installation




S = safety distance in mm
H1 = the lowest beam must not be placed more than 300mm from ground
H2 = the highest beam must not be placed less than 900mm from ground

The following formula allows to calculate the safety distance for the vertical installation:

S = (2000 x T) + 8 x (d – 14)

where d is the resolution of the photoelectric barrier in mm
K = 2000 mm/s is the speed of the hand
The expression (8 x (d – 14)) can never be lower than  0.
The minimum safety distance S is therefore 100mm.

If the safety distance calculated with the previous formula exceeds 500mm,
the following formula can be used as an alternative:

S = (1600 x T) + 8 x (d - 14)

where K = 1600mm/s is the speed of the body.  
The minimum safety distance S is therefore 500mm.