Sliding gate systems present a variety of hazards that can cause significant injury if not properly guarded and maintained. Whether motorized or manually-powered, these systems typically include heavy moving parts, pinch point hazards, and wear components that require periodic inspection and maintenance.
This article provides an introduction to the design and physics of cantilevered sliding gates. It also discusses known hazards and describes potential mechanisms of failure by revisiting the fact pattern from an actual case investigation. The experts at Robson Forensic have investigated a broad range of incidents involving physical security features, such as sliding gates, barrier arms, and overhead doors.
SLIDING GATE INJURIES - EXPERT ARTICLE
ANATOMY OF A CANTILEVERED SLIDING GATE
A cantilevered gate operates by sliding along a set of upper and lower roller assemblies that are mounted to counter balance posts. These posts are of a heavier construction than standard fence posts (often 3”-4” in diameter) as they must support the dynamic loads of the sliding gate assembly.
The longitudinal pipe members of the gate assembly ride in, and are held captive by, the roller assemblies. Regardless of position (opened or closed), the gate is in constant contact with the two upper and lower pairs of rollers. The gate is only in contact with left-most lower roller when the gate is partially to fully open.
Failure of any of these rollers, or structural failure of the sliding gate assembly, will affect the sliding motion of the gate and can cause the system to become inoperable and/or potentially dangerous.
SLIDING GATE HAZARDS
The following hazards relevant to sliding gates are well known within industry and have viable engineering solutions that provide effective protection. Other hazards may exist in your case depending on the specific system arrangement or environment where the gate is operated.
Crush Hazards - Crush hazards exist where it is possible to be caught in or between two objects in a system. The weight of the sliding gate assembly and the momentum of the gate both potentially present crush hazards.
The weight of the sliding gate assembly can be substantial, depending on the height of the fence, width of the opening, and the materials used to construct the gate. In the case described later in this article, our experts examined a chain link gate that measured 45 feet long by 6 feet tall, weighing approximately 800 pounds. The incident gate is not atypical: many of these devices are of a size and mass capable of causing significant crush injuries.
The momentum of the sliding gate assembly also presents a potential crush hazard where it meets the stationery latch post. Similar to residential garage doors, light curtain and automatic reverse protection can be incorporated into motorized sliding gate systems.
Pinch & Nip Point Hazards - Pinch and nip point hazards occur when a moving part contacts or rubs against or in close proximity to another part or surface. These hazards commonly exist in machinery and equipment that incorporate gears, pulleys, or rollers.
The points where the sliding gate assembly interfaces with the roller assemblies presents a pinch point hazard that should be guarded. Other pinch and nip point hazards may exist in motorized systems around the motor and drivetrain.
PRODUCT DESIGN HIERARCHY
Product manufacturers must ensure that hazards are engineered out of the product during the design process. If a hazard is inherent and cannot be designed out of the product, system, or process, the hazard must be properly safeguarded. In all cases, the user must be properly warned or instructed about dangers of the product. These steps form the fundamental principles and rules of practice for the safe and appropriate engineering of products, and are sometimes referred to as the hierarchy of hazard control.
The requirement for guarding and, more broadly, product safety is reinforced by a number of government and industry oversight organizations. In keeping with the intended security function of a gate, the mass and forces of the sliding mechanism cannot be eliminated, but in many instances it is possible to protect against exposure to the related forces.
MAINTENANCE & INSPECTION REQUIREMENTS – CASE EXAMPLE
Even well-designed systems can fail if proper maintenance is neglected. Our experts investigated one such case where a manually powered sliding gate failed catastrophically. In this incident, one of the rollers detached from the lower assembly, causing the ~800 pound sliding gate to tip over and fall on the plaintiff.
Deposition testimony from both plaintiffs and defendants in the case supported that the incident gate had become increasingly difficult to operate leading up to the date of the incident. Rather than remedying the condition, the facility utilized a group of employees to collectively slide the gate opened and closed. The plaintiff was working with a team of two other coworkers to open the gate at the time of the incident.
Inspection by our expert revealed signs of scuffing at the rim of the detached roller, consistent with it dragging at the pavement for an extended period of time, and consistent with prolonged bearing failure. At least one of the roller’s bearings showed signs of flattening.
The two remaining lower rollers were both “looking down,” i.e. angled downward toward the ground in the unloaded condition, consistent with prolonged bearing failure.
All rollers, including and especially the lower rollers, showed signs of inadequate lubrication: insufficient grease, dirty grease, and hardened grease. The failed roller bearings showed signs of corrosion and flattening, further indicating inadequate lubrication. As a result of inadequate maintenance the bearings in the lower rollers had failed.
Our expert was able to demonstrate that a lack of maintenance on behalf of the property manager created a dangerous condition that caused the plaintiff’s injury. His opinions were supported by industry standards, including manufacturer guidelines to periodically grease the roller bearings.
In line with our expert opinion, our client obtained a favorable outcome on behalf of the plaintiff.
SLIDING GATES, VEHICLE BARRIERS & OVERHEAD DOOR INVESTIGATIONS
The experts at Robson Forensic work with counsel for both plaintiffs and defendants to investigate a broad range of injuries involving physical security systems, including sliding gates, barrier arms, and overhead doors. These cases frequently rely on experts from our Facilities Engineering practice group, but depending on the fact pattern will sometimes involve experts specializing more specifically in mechanical or electrical engineering.
Contact us directly or submit an inquiry to be connected with an expert whose qualifications align with the technical demands of your case.
Facilities & Marine Engineering Expert
Christopher Fogarty is a Facilities Engineer with over 40 years of experience as a Maintenance Engineer and Chief Engineer at a large, state-of-the art public sports and entertainment facility. In the course of his career, he has been responsible for all technical aspects of Facilities Operations & Management, including equipment and building systems; health, safety, environment (HSE); and security.