Nicholas A. Petrucci, P.E., C.S.P.
According to the National Safety Council, in 2013 175,790 people were injured severely enough while using a ladder to require treatment at a hospital1. Although the cause of these unfortunate incidents often involves some type of misuse, ladder defects are frequently causative or contributory factors.
Portable ladders are generally classified as either step ladders or extension ladders. Articulating ladders have become popular in recent years, as they can be setup as a step ladder, an extension ladder or other useful configuration.
The most common types of ladder misuse are selecting the wrong ladder, using a damaged ladder, improper ladder setup and acting in an unsafe manner while on the ladder.
Examples of improper ladder selection include choosing a ladder that is too short and requires excessive reaching to perform the task at hand, or does not enable an extension ladder to extend three feet beyond the roof line. Use of a ladder with a weight capacity less than the weight of the user and anything that he or she may be carrying is another example of improper ladder selection.
Ladders should be inspected before each use. Damage or excessive wear generally renders the ladder unsafe and warrant its disposal.
Ladders should only be setup on dry, level, flat, firm, stable and high friction surfaces. All locking mechanisms should be checked for full engagement and the ladder should be inspected for stability before it is ascended. It is often wise to secure an extension ladder to the structure that it is leaning against. Before the ladder is setup the surrounding environment should be assessed for any hazards (e.g., low hanging power lines, foot traffic, door swings, high winds, etc.).
Ladders should only be used as intended by the manufacturer. Once on the ladder, the user should keep their center of gravity near the center of the ladder, and not stand above a safe working height. Excessive reaching and sudden movements should be avoided. Three points of contact should be maintained (i.e. only one hand or foot not in contact with the ladder) while using a ladder, especially when ascending or descending it.
For the most part ladder defects can be characterized as a design defect, manufacturing defect or inadequate warning.
A design defect occurs when a ladder is not reasonably safe for not only it intended, but its reasonably foreseeable, use due to the deficient specification of its geometry, material, manufacturing process, etc. Design defects are most problematic as they affect all ladders of a certain make and model.
A manufacturing defect occurs when a ladder is not reasonably safe for its reasonably foreseeable use due to an unacceptable deviation from its design specifications. Manufacturing defects are generally not as problematic as design defects as they typically only involve a batch or a smaller number of ladders.
Inadequate warnings fail to warn of hazards associated with using the ladder, or fail to instruct the user how to use or setup the ladder in a safe manner. Labels containing these instructions and warnings are affixed to the ladder. Ladder labeling requirements are specified by ANSI2.
Design Defect and Improper Inspection before Use
A worker in a warehouse was standing on a step ladder while waiting for the next pallet of items to stack on a storage shelf. The ladder suddenly became unstable and he fell from it. My inspection of the ladder revealed that its sudden instability was the result of the failure of one of the rivets that secured a rail to the top cap. My analysis determined that the design of how the rivets connected the ladder front rails to its top cap was defective. I agreed with opposing counsel that the ladder met all applicable industry standards and design verification tests; however, this did not relieve the manufacturer of the duty to properly design the ladder rail to top cap connections. A complicating factor was that the ladder was badly worn, in a way that weakened the rivet, and should have been discarded prior to the incident.
Design Defect and Manufacturing Defect
A homeowner was using an articulating ladder in the extension ladder configuration to change an exterior light. While ascending the ladder, its top section separated from the rest of the ladder, resulting in the homeowner suddenly falling to the ground. After inspecting the ladder, I determined that the cause of the incident was the failure of the locking mechanism that secured the top section of the ladder. Upon inspecting the locking mechanism more closely I determined that it was exposed to excessive stress levels due to a loose fit with its receiving hole, and with a help of a metallurgist determined that there was an inclusion (defect) on the fracture surface that weakened the locking mechanism.
Design Defect and Misuse
A retail store worker fell from a step ladder. After examining the ladder, I determined that depending how the ladder was removed from its storage position, its spreader bars could become inverted when the ladder was opened. This configuration, difficult to describe without photographs, prevented the spreader bars from being locked when the ladder was setup for use, which reduced its stability. I attributed this anomaly to a design defect that allowed the inversion of the spreader bars to occur under reasonably foreseeable conditions. However, I also determined that the worker was standing on the wrong side of the ladder (i.e., the side without the steps) at the time of the incident.
It is essential for ladder manufacturers to adhere to applicable industry standards. However, it is not, and cannot be, the intent of industry standards to specify all design and manufacturing requirements for ladders. It should be understood that if a ladder fails to meet the requirements of an applicable industry standard, it can be deemed defective. However, meeting all of the requirements stipulated in applicable industry standards alone does not prove that the ladder is not defective.
Nicholas A. Petrucci, P.E., C.S.P., is president of Petrucci Engineering Consultants, LLC, www.petrucciengineering.com. He analyzes equipment and machinery failures, and conducts safety assessments. Mr. Petrucci can be reached at email@example.com or 724-327-0529.
- “Ladder Safety One Rung at a Time.” Ladder Safety One Rung at a Time. National Safety Council, n.d. Web. 16 May 2016. <http://www.nsc.org/learn/safety-knowledge/Pages/Ladder-Safety-One-Rung-at-a-Time.aspx>.
2. American National Standard Safety Requirements for Portable Metal Ladders. ANSI Standard A14.2-2007.