For human body protection, Bruce said: (12-05 07:44)

>I'll bow to Richard's input of 12/04, 12:45 advocating use of a light
>beam to detect an obstruction. His idea makes mores sense than >trying to fabricate and hang movable "bumper doors".

And later (two messages down) Jay made a good point that light beam cannot be trusted fully.

I must agree with Jay on this issue. In an outdoor environment, there are just too many matters can impact the effectiveness of an optical instrument, such as sunlight, snow, dust, bird dropping, and other insects.

If the "bumper doors" style of an elevator is too complex to fit, I have a simple solution. Tie a string of wire across the closing edge of one door (or both doors for double safeguarding). To avoid the string to be clampped by the closing doors, the string can be installed a few inches away from the door edge and inside the doom. Such that in case an object is in between when the doors are closing, the object will trip the wire and pull the (kind of) circuit breaker to cut off the power to the motors.

Regards, Oliver