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The Imperative of Understanding Rating Charts: A Look at Safety and Environmental Impacts

Updated: Sep 10, 2023

Safety and operational efficiency are paramount in crane operations, particularly critical and complex lifts. Misunderstandings around the interpretation and application of crane rating charts can lead to compromised safety and environmental consequences. Here is a thorough look at this multifaceted issue.

Rating Charts - 75% Reductions
Rating Charts - Its Complicated

Rating Charts: Global Standards and Local Context

Crane rating charts are influenced by international norms such as DIN/ISO and ANSI/ASME, which typically use 75% and 85% rating charts respectively. The Pressure Equipment, Cranes and Passenger Ropeways Regulation (PECPR) and Approved Code of Practice for Cranes (ACOP Cranes) recommend a 78% tipping load capacity in New Zealand. However, due to the absence of 78% charts from manufacturers, a 75% chart is commonly used for static cranes.

Special Conditions: A 66% rating chart applies according to ACOP for Cranes guidelines for pick-and-carry and crawler cranes in non-stationary states. Tracking or walking.

Let's Break Down these numbers.

Crane operators and project managers should know that the chart displayed on crane safe load indicators and in rating charts in New Zealand have a range between 0 and 100% of safe lifting capacity where 100% is a 75% reduction or 75% chart. So effectively the crane has a maximum lift that equates to 75% of tipping load. On the 75% charts, this is shown as 100% of capacity. The following drawing works to illustrate this.

Crane Chart Rating Reductions
Crane Chart Rating Reductions

Arbitrary Capacity Reductions

There is a prevalent practice among some project managers to add a further 20% safety buffer on the crane's rated capacity. This reduces the 100% failure point, already conservative at 75%, to an even lower 60%. Effectively, 80% of the crane's rating chart.

This thinking appears to be based on increasing the safety factor of each lift. However, very little consideration is taken to step back and consider the overall project risk.

Reduced Rating Chart by Site to 80%
Reduced Chart by Site to 80%

Such a decision can result in unintended consequences. Have we really made the site safer? Let us look at some unintended consequences.

Unintended Consequences:
  • Reduced Operational Efficiency: A larger crane demands more time and equipment for setup.

  • Higher Risks: A larger crane often results in greater ground-bearing pressure. A larger crane may introduce more moving parts, requiring greater resources to establish the crane. You may also require more people interactions, increasing risk as equipment moves and prepares for lifting.

  • Environmental Impact: Utilising larger cranes often involves additional on-the-road movements, increasing greenhouse gas emissions. Two trucks may become three trucks, etc.

  • Increased Costs: A larger crane normally has a higher rental cost.

A Balanced Approach: Safety, Efficiency, and Environmental Considerations

Focusing on specific safety metrics and controls would yield better outcomes than an arbitrary capacity reduction. Key areas of focus could include:

  • Site / Job Planning

  • Lift Planning

  • Rigging Plans

  • Load Weight Calculations

  • Operator Competency / Rigger Competency

  • Ground Bearing Calculations (Geotechnical Advice)

Are we lifting the load down from height? Are we lifting it from the ground? Are we gaining weight instantly or slowly increasing the weight to a known level?

The Need for a Comprehensive Risk Assessment

The decision to reduce capacity by a blanket figure should not be made lightly, as it often requires larger cranes with their risks and environmental implications. The question arises: Are we enhancing safety or shifting risks and environmental burdens?

Stop the press. Don't discard a larger crane.

The argument works the other way too. But should be made on its own merits. A larger crane may have considerable advantages. However, the message here in this post is that these advantages should be weighed against safety, efficiency, and environmental considerations.

So what's the Key?

Have the conversation. Get in touch with McLeod and let's talk through the options and the key parts of the project. There is a sweet spot and we are keen to help you find it.

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