Why can non-contact safety features, for radiation shielding doors, not compensate missing limitation of closing forces
Compared with common power operated doors, radiation shielding doors possesses two additional safety-relevant features. On one hand, Door leafs can have a depth of more than 300 mm, up to 2000 mm and on the other hand, door leafs weight more than 10 kN, up to 1300 kN.
These enormous depth of the leaf grant space for a person to stand in between the inner and outer end of the sliding door leaf, without being recognized by a non-contact safety feature. Non-contact safety features are installed before, and, or behind the passage. The intermediate space is not monitored. Without a working force limitation, a person would be crushed between the closing edge and the wall.
Also narrower door leafs are not safe with a solely non-contact safety protection. Given the case that a person grabs into the area of the doors front edge near to the shearing edge, while the door is closing, and triggers the non-contact safety device, because of the significant mass the stopping distance could be too long to prevent a crushing or shearing of limbs.
Complementary be mentioned, that someone grabbing into the danger spot isn’t unusually. Maybe you’ve already seen someone grabbing into closing elevator doors, trying to trigger the light curtain and reopening the door for another person. With light elevator doors that may only lead to a mild clamping, but in case of heavy shielding doors this may result in serious injuries.
A relief for both cases is a limitation of the closing forces, in compliance with EN 12453, using contact stripes.
A present risk assessment, which has examined the described issue, comes to the following conclusion. “The operational safety can’t be solely implemented by non-contact safety features. An effective safety feature is the limitation of the closing forces, triggered by contact stripes. The resultant closing forces have to meet the restrictions of EN 12453.”