Your browser is currently set to block JavaScript.

For full functionality of this site it is necessary to enable JavaScript. Here are the instructions how to enable JavaScript in your web browser.

After enabling javascript, please refresh the page to go back to site with full functionality

Would you turn off/on JavaScript?

It's a widely used language that makes the web what it is today, allowing for websites to be more responsive, dynamic, and interactive. Disabling JavaScript takes websites back to a time when they were simple documents without any other features.

What are the advantages of using JavaScript?

Speed. Since JavaScript is an 'interpreted' language, it reduces the time required by other programming languages like Java for compilation. JavaScript is also a client-side script, speeding up the execution of the program as it saves the time required to connect to the server.

banner ad
Experts Logo


Stepladder Instability Testing

By: Dr. Irving Ojalvo

Tel: (800) 358-9909
Email: Technology Associates

View Profile on

According to Consumer Product Safety Commission (CPSC) accident estimates, tens of thousands of stepladder accidents requiring emergency room treatment occurred annually in the United States. Approximately 85-90% of these accidents involve the user falling from the ladder and 8-9% of these injuries are serious enough to require that the victim be admitted to a hospital. In addition to posing a severe health concern, these accidents have significant loss-of-wages and high medical expense implications.

Having investigated numerous stepladder falls over the years, we have found it very common to learn that ladder accident victims are unaware of the cause of their falls and it is typical for them to respond to questions regarding causation with answers such as: "The ladder just gave way", or "It was sudden, I don't know what happened", or equivalent statements. One possible cause of such accidents is associated with use of the common four legged A-shaped stepladder, which can easily be accidentally positioned such that only three of its legs are contacting the ground. This situation can also go unperceived until it is too late to avoid an accident.

Three-leg contact can develop under a number of situations such as set-up on an uneven surface or when climbing, sliding, pivoting or "walking" a flexible ladder along the ground as the user's work progresses. Dr. John Morse has cited a subtle type of unperceived three-leg stepladder contact named "Type-II racking", which occurs during climbing as follows. After the climber has one foot on the floor with his other foot on the first step, and one or both hands on the front rails at chest height, he pulls himself upward with one arm and attempts to keep his body straight. This imposes a torque about a vertical axis to the ladder. This torque, combined with the climber's pulling force (which is necessary to raise his weight to the next step), tends to unload the rear legs. With these legs offloaded, and while this torque is still applied, the ladder twists or "racks" in the direction of the applied torque. When the climber's foot then leaves the floor and reaches the first step, weight is shifted back onto the rear legs of the racked (slightly twisted) ladder. When this occurs, only one of the ladder's rear legs can contact the ground. If this goes undetected, the climber has unknowingly created a three-legged ladder and the potential for instability, should center of gravity diagonal-crossover occur later after subsequent climbing or use.

The danger of falling arises when the unsuspecting climber shifts his center of gravity, causing the ladder's elevated rear leg, to impact the ground. This is likely to occur when the user lifts one foot while stepping from one level to the next or shifts his weight while working. When this happens, large and rapid forces and the user's overcompensating reflexes can cause him to lose his balance and fall.

In the sample test video linked here, a harnessed test subject climbed a 6 ft metal ladder, in the three-legged condition. The climber ascended the first step of the ladder and applied a hand force to the right side-rail, creating a three-leg stability condition. The climber then continued ascending, in a normal manner, to the fourth step. Upon reaching that step, the climber shifted his entire weight onto his right foot, which was located near the right side rail. This shifted the climber's weight over the diagonal stability line and the ladder moved suddenly. Once the ladder crossover motion was initiated, the climber attempted to maintain and regain his balance.

Falling Ladder Climber

The above sequence of photos is representative of the ladder-climber system response to the crossover event. The ladder initially rocks to the climber's right (because the right rear leg is initially off the ground) until the right rear leg strikes the ground. After the right rear leg strikes the ground, the climber's feet and the ladder continue to move to the climber's right causing the climber's body to move into an almost horizontal position with his head pointed away from the side of the initially raised leg (in this case towards the climber's left).

Based on our research, Type II racking can easily lead to the previously described three-legged condition, even when a stepladder meets the present ANSI (Type-I) racking standard. Based on dynamic testing, a vertical rear leg lift of as little as 1 inch is sufficient to cause a ladder user to fall upon unanticipated crossover. This scenario is consistent with many accident investigations and offers a likely explanation for stepladder fall accidents when there is no obvious cause. We have found that the minimum leg lift-off required to cause a ladder user to fall upon crossover is less than 1 inch and also depends greatly on the agility of the ladder climber.

Dr. Irving Ojalvo was, at the time of this article's publication, the Chairman of Technology Associates (, a forensic engineering firm with offices in New York City and Connecticut. The firm's technical personnel, all of whom have advanced degrees, perform accident reconstruction involving issues of biomechanics, mechanical, traffic, and human factors engineering.

©Copyright - All Rights Reserved


Related articles


7/14/2009· Forensic Analysis

Slip and Fall Accidents

By: Dr. Irving Ojalvo

Second to automobile accidents, accidents due to falls are the leading cause of injury and death. Of these, accidents due to slipping (not tripping) form a large proportion. Slipping may occur on floors, walkways, and stairs or steps. For Introductory purposes, however, the present discussion will be limited to slipping on flat surfaces such as a floor or sidewalk.


2/27/2017· Forensic Analysis

Forensic Document Examination Reveals Altered Deed of Trust in Divorce Dispute

By: Mike Wakshull

The divorce had been finalized 15 years earlier. The husband had moved on with his life. He was happily remarried and enjoying his retirement years. The ex-wife could not let go. She sued in the Superior Court of Los Angeles claiming the husband would not relinquish rights to real property and other interests that had been part of the divorce settlement.


7/14/2009· Forensic Analysis

Golf Car Hazards

By: Dr. Irving Ojalvo

According to the Consumer Products Safety Commission (CPSC), there are approximately 10,000 golf car related injuries requiring emergency room treatment in the US each year. One significant mode of injury in golf car accidents is passenger ejection, which can lead to serious injuries, especially of the head. Based on CPSC statistics, roughly 35% of golf car accidents involve a person falling out of the car. In addition to ejection accidents, at least 10% of golf car accidents involve a rollover and statistics indicate that such accidents are roughly twice as likely to lead to injuries requiring a hospital stay as non-rollover accidents.

; broker Movie Ad

Follow us

linkedin logo youtube logo rss feed logo