Posted By Graham Glenn
An accident has occurred while using an extension ladder and I wonder if anyone has experience or a theory of how it could have happened.

It involved a double extension ladder extended by a rope fitted to one stile. The catch between the two parts of the ladder was in two pieces, each spring-loaded to pass over a rung automatically and both were found to be in good order after the accident. The ladder was held away from the wall by one man while a second pulled on the rope to extend it to the required height. The ladder was then placed against the wall and 'bounced' into position. One man climbed the ladder and described the ladder swaying.

When the man reached the upper part of the ladder, the extension slid downwards to the unextended position. The movement caused the man to fall.

The ladder did not break and after careful examination was returned into service.

Can anyone suggest a mechanism for such an incident?

Posted By Graham Glenn
These points have occurred to me. The first check that the catch has engaged is that the extension stays up. Each part of the catch is independently spring-loaded towards the engaged position. Bouncing the ladder into position and the report of the ladder swaying in use suggest to me that it is highly unlikely that the catches would both remain in precarious positions.

To release the catches, the extension is raised part way to the next rung. A deflector beneath the catch strikes the rung during downward movement and pivots upwards to close the opening to the catch. A pause between rungs allows the deflector to fall so that the catch can move into the engaged position.

The deflector has no effect when raising the ladder.

I am struggling with an explanation for this incident.

Posted By Robert K Lewis
I would look more closely at the statement of events again. This sounds suspiciously like the ladder was not properly erected and the extension catch engaged. Bouncing ladders is not good practice and one must question other work practices.

Bob

Posted By Graham Glenn
Bob,
Thank you for your comments. I agree with you, but I still have difficulty explaining how the ladder remained extended long enough for a man to climb it. Before coming to a conclusion, I am keen to fully investigate the description that I have been given, hence my request for comments.
Graham

Posted By Graham Glenn
Ron,
Thank you for your comment. The ladder could not be used upside down, because the catches could not engage at all. It occurred to me that it could have been used back to front so that the upper part was behind the lower and was effectively pushed away as the man climbed it, but that is not supported by the witness descriptions.
Graham

Posted By Graham Glenn
Martin,
That is an interesting thought. Thank you.

Graham

Posted By Chris Bridle
Sounds very much like the ladder extension was not suitable engaged to begin with,not to blame the workers they may have been unaware of this. Best thing that has been mentioned earlier would be to contact the manufacturer to help solve this. Alternatively try all ways of extending the ladder and repeating the failure of the locking device. Most importantly until you've reached the source of the problem and ruled out a mechanical failure rather than an operators mistake, I would remove the ladder from service immediately.
Good Luck!

Posted By Fred Pratley
How is the catch designed to operate when collapsing the extension?

After being disengaged, does it permit movement past several stiles at a go or does it need to be relesed to pass each stile? Is this current design or have you got an "old" ladder?

Clearly the locking device was not engaged - checking the extension stays up could mean the extension has simply "stuck" in place as ladders are prone to do.

I would mark the underside of the catch with bright paint so that it can be seen to be past the relevant stile when extended into position.

Posted By Granville Jenkins
Well, the warning signs were there that something was not quite right and people were either not paying attention or chose to ignore the facts- as soon as the operative on the ladder commented that the ladder 'felt like it was swaying' he should have stopped ascending the ladder and slowly made his way back down - then the ladder should have been thoroughly checked out.

From what has been described it is likely that during the 'bouncing' operation the top and bottom sections had jumped and the latching mechanism was not engaged fully - which would explain why the ladder was swaying, especially as the ladder still functions correctly after the event. The only other likely 'defect' to make a ladder sway is where the connections between the rung's and stiles have loosened with use and age and as the ladder is ascended a motion is set in place which causes the ladder to sway (fact based on practical experience)- if the swaying is too bad the ladder should be condemned.

Hopefully the person who fell was not too badly hurt and the events can be put down to experience - hindsight being a wonderful teacher!

Regards
Granville