JLG Near Disaster

[MikePhua]

A Routine Lift Turns Dangerous
A rough-terrain aerial lift suffered a serious incident when it nearly toppled during a routine construction task. The machine was a telescopic boom lift rated for high reach and moderate lifting capacity, but the operator attempted to extend the boom well beyond the machine’s safe working envelope while the lift was positioned on uneven ground. The boom began to dip, and the machine shifted violently, forcing nearby workers to react quickly and prevent further escalation.
Although no one was injured, the event highlighted how large mobile platforms can fail when basic safety principles are ignored.
Boom lifts use hydraulic cylinders and counterweights to maintain balance. Their stability calculations assume flat terrain, controlled loads, and measured reach. Any change to those factors can drastically reduce the stability margin. In this case, the combination of boom extension, off-center load, and soft soil created the perfect conditions for instability.
Misjudging the load chart is one of the most common causes of accidents involving aerial devices. Studies from multiple construction equipment insurers suggest that over 40% of boom lift accidents involve improper use of load limits or positioning.

What Makes a Telescopic Boom Lift Vulnerable
An aerial lift looks stable because of its large chassis, but the physics behind it is extremely sensitive. When a boom is extended, the center of gravity moves far outside the wheelbase. Even small slopes can change stability dramatically.
Key factors that reduce stability include:

• Boom angle reduction
  
• Boom extension
  
• Side loading caused by swinging a load
  
• Soft or sloped ground
  
• Sudden operator inputs
  
• Wind loading
  

This particular incident involved several of these at the same time. The operator attempted a horizontal reach with insufficient counterweight support, causing the machine to “walk” on its tires and rock violently.
Operators sometimes assume that outriggers (if present) or foam-filled tires guarantee stability. They do not. They simply increase the safety margin when used correctly.

JLG Equipment Background
JLG Industries is one of the world’s leading manufacturers of aerial access equipment. The company was founded in the late 1960s and saw rapid growth in the 1970s due to increased demand for safe working platforms in construction and maintenance.
Important background points:

• JLG was an early pioneer in the boom lift market
  
• Their machines improved productivity compared to scaffolding
  
• They expanded globally in the 1990s and 2000s
  
• They reported multi-billion USD annual sales during peak construction cycles
  

Telescopic boom lifts, scissor lifts, and articulated booms became essential tools worldwide. Market studies show that over 150,000 aerial lifts are sold annually across all manufacturers, with a significant share attributed to JLG.
The company designs machines to meet strict safety standards, but operator misuse continues to be a leading cause of incidents.

Mechanical Response and Factors Leading to Failure
The machine behaved as expected from a physics standpoint. When the boom was pushed beyond its safe envelope, the hydraulic system attempted to compensate, but hydraulic pressure alone cannot counteract the moment created by an extended load.
Relevant terminology:

• Load Moment: the tendency of a load to cause tipping; product of weight and distance
  
• Counterweight: mass added to oppose load moment
  
• Tipping Axis: line between wheels about which a machine can topple
  

In emergency conditions, operators may attempt to retract the boom quickly, but rapid movement can make instability worse by shifting weight dynamically.
In this case, the operator stopped moving, the machine settled, and workers placed blocking material under low tires to prevent a full rollover before recovering the unit.

A Story from Another Worksite
A similar scenario happened at a manufacturing plant during a nighttime maintenance shift. A boom lift operator attempted to reach a high ventilation system over a truss beam. The worker extended the boom horizontally instead of working vertically, unknowingly operating at less than 25% of rated lifting capacity for that angle.
As the boom extended, the machine leaned toward a steel column, scraping it before stabilizing. That incident triggered a company-wide rule requiring load chart certification for all lift operators before they could work unsupervised.

Worksite Safety and Prevention
Near disasters like these are usually preventable. Most incidents stem from rushed work, lack of planning, or poor understanding of equipment limitations.
Common practices that reduce risk include:

• Conducting daily stability checks
  
• Inspecting ground conditions
  
• Verifying load charts before lifting
  
• Using spotters during critical operations
  
• Avoiding horizontal reaches when possible
  
• Training operators in platform physics
  

Many companies implement the “three-person rule” for aerial lift work: operator, spotter, and supervisor must agree before performing high-risk maneuvers.

Engineering Controls and Modern Technology
Modern lifts include features designed to prevent accidents:

• Automatic load sensing
  
• Boom angle sensors
  
• Tilt alarms
  
• Speed derating when limits are reached
  
• Hydraulic interlocks preventing unsafe movements
  

However, sensors cannot solve every problem. For example, load sensors may not prevent side loads or soft-ground sinking. Field studies show that sensor-based systems reduce incidents by 20–30%, but they cannot fully compensate for poor decision-making.
Future advancements may include:

• Real-time ground pressure monitoring
  
• AI-based operator guidance
  
• Auto-stabilizing outriggers
  
• Dynamic load prediction models
  

Lessons Learned
This event reinforces several key principles of safe lift operation:

1. Boom lifts become unstable quickly during horizontal reach
   
2. Uneven ground multiplies the risk of tipping
   
3. Load charts must be checked before any lift
   
4. Sensor warnings are not optional suggestions
   
5. Stopping movement is often safer than reacting aggressively
   
6. Team awareness prevents escalation
   

Construction workers often believe they can “feel” stability through experience. In reality, humans are terrible at intuitively judging load moment. Machines tip suddenly, with little warning.

Industry Recommendations
Based on safety data and accident analysis, the following practices are widely recommended:

• Use cribbing or mats on soft ground
  
• Keep the boom above 45 degrees whenever possible
  
• Never exceed horizontal reach limits to “just finish a job”
  
• Establish mandatory risk briefings before high lifts
  
• Enforce certification and recertification every 3 years
  
• Encourage reporting of near misses
  

Safety culture is strengthened not by avoiding discussion of mistakes, but by documenting and sharing them.

Conclusion
The near disaster involving a telescopic boom lift demonstrates the combined impact of physics, training, and site conditions. Heavy equipment is engineered with remarkable capability, but its stability envelope is narrow. Failure often results not from mechanical malfunction but from misjudged operation.
Accidents that “almost” happen are valuable warnings. They remind the industry that elevating workers tens of feet above the ground demands planning, communication, and respect for the physics that govern every movement of a multi-ton machine.