Specialized Lifts, Multi-Crane Operations, and Critical Lifts

Introduction to the Chapter

This chapter covers lifting situations that go beyond the ordinary: specialized lifts, multi-crane operations, and critical lifts. For the Red Seal exam, you must not only understand the physical principles involved, but also the planning procedures, load calculations, and applicable regulatory requirements. This chapter prepares you to identify risks, perform the required calculations, and apply best practices in accordance with Canadian standards.

1. Definitions and Classification of Lifts

1.1 Specialized Lift

A specialized lift is a lift that requires particular precautions due to the nature of the load, the work environment, or the equipment used. It is not necessarily a heavy lift, but rather a lift that presents unusual challenges.

Common examples:

Oversized loads (excessive length, width, or height);

Loads with an offset or unknown centre of gravity;

Fragile or high-value loads (transformers, turbines, nuclear components);

Submerged or partially buried loads;

Lifts in confined spaces or near power lines.

1.2 Critical Lift

A critical lift is a lift where a failure could result in serious injury, loss of life, major property damage, or significant environmental consequences. The classification of a lift as critical depends on several factors:

Factor	Example of Criticality Threshold
Load mass	Greater than 75% of the crane's rated capacity
Risk to personnel	Lifting over occupied areas
Load value	Irreplaceable equipment or very high replacement cost
Operation complexity	Multi-crane, cantilever lift, load rotation
Environment	Proximity to power lines, high wind, unstable ground

1.3 Multi-Crane Operation

A multi-crane operation involves the use of two or more cranes to lift the same load. This configuration is used when:

The load mass exceeds the capacity of a single crane;

The geometry of the load requires precise orientation control;

The site does not allow positioning a single crane of sufficient capacity.

2. Planning Specialized and Critical Lifts

2.1 Mandatory Planning Steps

In accordance with best practices and applicable CSA standards (CSA Z150 for mobile cranes), every critical lift must be the subject of a written lift plan. The steps are:

26.Load analysis: determine the exact mass, centre of gravity, anchor points, and stability.

27.Crane analysis: verify capacity at the planned configuration (boom length, angle, radius, counterweight, outriggers).

28.Site analysis: soil bearing capacity, slopes, obstacles, power lines, wind.

29.Selection of rigging hardware: slings, shackles, spreader bars, equalizer beams, jacks.

30.Determination of angles and tensions: calculate the forces in each sling leg.

31.Drafting the lift plan: a written document detailing all steps, responsibilities, and emergency procedures.

32.Pre-lift meeting (tailgate meeting): communicate the plan to the entire team.

2.2 Calculating the Centre of Gravity

The centre of gravity of a load is the point where the total mass is considered to be concentrated. For a load composed of multiple elements, the overall centre of gravity is calculated as follows:

CG overall = (Σ (mᵢ × dᵢ)) / Σ mᵢ

Where:

mᵢ = mass of each element (kg)

dᵢ = distance of each element from a reference point (m)

Example: A beam 8 m long, composed of two sections: the first weighing 3,000 kg over 3 m, the second weighing 5,000 kg over 5 m.

CG = (3,000 × 3 + 5,000 × 5) / (3,000 + 5,000) = (9,000 + 25,000) / 8,000 = 34,000 / 8,000 = 4.25 m from the reference point.

Exam trap: The centre of gravity must be located between the rigging points. If it is not, the load will tip. Always verify that the CG is within the polygon formed by the attachment points.

2.3 Calculating Tensions in Slings

For a load suspended by two slings forming an angle θ with the vertical, the tension in each sling is:

T = (m × g) / (2 × cos θ)

Where:

T = tension in each sling (N)

m = mass of the load (kg)

g = 9.81 m/s² (gravitational acceleration)

θ = angle between the sling and the vertical (degrees)

Table of tension factors based on the included angle (angle between the two slings):

Included angle (α)	Angle with vertical (θ)	Multiplier factor per leg
0°	0°	0.50
30°	15°	0.52
60°	30°	0.58
90°	45°	0.71
120°	60°	1.00
150°	75°	1.93
180°	90°	∞ (prohibited)

Rule of thumb: The included angle between two sling legs must never exceed 120°. Beyond this, tension increases exponentially and load stability decreases.

3. Multi-Crane Operations: Principles and Procedures

3.1 Load Distribution Between Cranes

In a multi-crane operation, the load is distributed between the cranes based on the position of the centre of gravity and the attachment points. The load supported by each crane is inversely proportional to the distance between the CG and the attachment point of the other crane.

Formula for two cranes:

F₁ = (m × g × d₂) / (d₁ + d₂)

F₂ = (m × g × d₁) / (d₁ + d₂)

Where:

F₁ = force supported by crane 1 (N)

F₂ = force supported by crane 2 (N)

d₁ = distance between the CG and the attachment point of crane 1 (m)

d₂ = distance between the CG and the attachment point of crane 2 (m)

Example: A load of 20,000 kg, CG at 2 m from crane A and 3 m from crane B.

F_A = (20,000 × 9.81 × 3) / (2 + 3) = 588,600 / 5 = 117,720 N ≈ 12,000 kg

F_B = (20,000 × 9.81 × 2) / (2 + 3) = 392,400 / 5 = 78,480 N ≈ 8,000 kg

Verification: F_A + F_B = 12,000 + 8,000 = 20,000 kg ✓

3.2 Golden Rules for Multi-Crane Operations

70.Reduced capacity: Each crane must never be loaded to more than 75% of its rated capacity in a multi-crane operation. This safety margin compensates for dynamic variations and distribution inaccuracies.

71.Single lift director: One person must direct the operation. The signalers of the other cranes relay instructions to the lift director.

72.Slow and coordinated movements: All movements must be slow, synchronized, and planned. No independent movement is permitted.

73.Constant communication: Use two-way radios on dedicated channels. Voice commands must be standardized.

74.Monitoring of boom angles: The boom angles of each crane must be continuously monitored to avoid boom collisions.

75.Mandatory written lift plan: Any multi-crane operation is automatically classified as a critical lift.

3.3 Load Transfer Techniques

Load transfer between two cranes is a delicate maneuver carried out using three methods:

Method	Description	Advantage	Risk
Vertical transfer	Crane A lifts the load, crane B attaches, then crane A slowly releases	Simple, precise control	Requires perfect coordination
Horizontal transfer	Both cranes move horizontally to transfer the load	Allows moving the load over a long distance	Risk of swinging
Rotation transfer	The load is pivoted around a vertical axis, each crane supporting one end	Ideal for changing orientation	Requires cranes of different capacities

4. Specialized Lifts: Techniques and Equipment

4.1 Lifting Loads with an Offset Centre of Gravity

When the CG is not at the geometric centre of the load, adjustable spreader bars or equalizer beams are used. The spreader bar allows positioning the attachment points so that the CG is directly under the hook.

Calculating the attachment point position on the spreader bar:

x = (L × m₂) / (m₁ + m₂)

Where:

x = distance of the attachment point from the end of the spreader bar (m)

L = total length of the spreader bar (m)

m₁ = mass of the load on side 1 (kg)

m₂ = mass of the load on side 2 (kg)

4.2 Lifting Long and Flexible Loads

For long loads (beams, pipes, piles), the main risk is buckling or deformation under bending stress. The rules are:

Use a spreader bar or lifting beam to keep the slings vertical;

Space the attachment points at approximately 1/4 and 3/4 of the load length;

If the load is flexible, add intermediate support points;

Calculate the maximum allowable deflection: δ_max = (5 × w × L⁴) / (384 × E × I) where w = linear load, L = length, E = modulus of elasticity, I = moment of inertia.

4.3 Lifting Submerged or Buried Loads

These lifts present a major risk: the adhesion or suction force that adds to the load mass. The total force to be lifted is:

F_total = m × g + F_adhesion

The adhesion force can reach 30 to 50% of the load mass. Safety rule: If the load does not release after an attempt at 100% of the crane's capacity, stop immediately. Never exceed the rated capacity to attempt to pull a load free.

4.4 Lifting in Windy Conditions

Wind affects the stability of both the load and the crane. Typical limits are:

Wind speed	Effect	Required action
0 – 30 km/h	Negligible effect	None
30 – 45 km/h	Noticeable swinging	Reduce load by 10%
45 – 60 km/h	Significant swinging	Reduce load by 25%; stop lifts of large-surface loads
> 60 km/h	Risk of loss of control	Complete stop of operations

Calculating wind force on a load:

F_wind = 0.5 × ρ × V² × A × Cd

Where:

ρ = air density (≈ 1.2 kg/m³)

V = wind speed (m/s)

A = projected area of the load (m²)

Cd = drag coefficient (0.8 to 1.2 for flat shapes)

5. Regulatory Requirements and Canadian Standards

5.1 CSA Z150-18 — Safety Code on Mobile Cranes

This standard is the primary reference in Canada for mobile cranes. The relevant articles for this chapter:

Article 4.3: Lift plan — every critical lift must have a written plan approved by a competent person.

Article 4.4: Mandatory pre-lift meeting before any critical lift.

Article 5.2: Verification of crane capacity at the planned configuration.

Article 7.1: Inspection of rigging hardware before each use.

Article 9.2: Load limits for multi-crane operations (75% of capacity).

5.2 CSA B167-16 — Overhead Cranes and Gantry Cranes

Although this standard applies primarily to overhead cranes, it contains requirements on slings and rigging hardware that also apply to mobile cranes.

5.3 Canada Labour Code — Mobile Crane Regulations (SOR/88-69)

This federal regulation applies to mobile cranes in federally regulated businesses. Key articles:

Article 14: Operator training and certification.

Article 17: Daily inspection before use.

Article 21: Load limits — never exceed the rated capacity.

Article 24: Multi-crane operations — requirement for a designated supervisor.

5.4 Canada Occupational Health and Safety Regulations (COHSR)

Article 12.10: Minimum distance of 3 m between any part of the crane and a power line of less than 75 kV.

Article 12.11: Minimum distance of 5 m for lines from 75 kV to 250 kV.

Article 12.12: Minimum distance of 10 m for lines over 250 kV.

Table of minimum distances from power lines:

Line voltage	Minimum distance
≤ 75 kV	3 m
75 kV – 250 kV	5 m
> 250 kV	10 m

6. Advanced Calculations for Critical Lifts

6.1 Dynamic Load Factor

During lifting, the load is subjected to dynamic forces due to acceleration, braking, and crane movements. The dynamic load factor (or impact factor) is:

F_dynamic = F_static × (1 + v² / (g × δ))

Where:

v = lifting speed (m/s)

g = 9.81 m/s²

δ = elastic deflection of the system (m)

In practice, a factor of 1.1 to 1.25 is commonly used for normal lifts. For critical lifts, a factor of 1.5 is recommended.

6.2 Calculating the Effective Capacity of a Crane in Multi-Crane Operations

The effective capacity of each crane in a multi-crane operation is:

C_effective = 0.75 × C_rated

Where C_rated is the crane's capacity at the planned configuration and radius.

Example: A crane has a capacity of 50,000 kg at a radius of 10 m. In a multi-crane operation, its effective capacity is 0.75 × 50,000 = 37,500 kg.

6.3 Ground Stability Verification

The pressure exerted by the outriggers on the ground must be less than the soil bearing capacity.

Pressure = F / A

Where:

F = force exerted by the outrigger (N)

A = effective contact area (m²)

Typical bearing capacities:

Soil type	Bearing capacity (kPa)
Compact rock	2,000 – 5,000
Compacted gravel	300 – 500
Compacted sand	200 – 300
Firm clay	150 – 250
Soft clay	50 – 100
Peat / fill	< 50

If the pressure exceeds the bearing capacity, use load-spreading plates (plywood or steel mats) to increase the contact area.

7. Emergency Procedures and Risk Management

7.1 Emergency Plan for Critical Lifts

Any critical lift plan must include:

Evacuation procedures for the lifting area;

Emergency services contact information;

Rescue procedures for working at height;

Emergency load lowering procedures;

Responsibilities of each team member in the event of an incident.

7.2 Risk Analysis (FMEA)

Failure Mode and Effects Analysis (FMEA) is a systematic tool for identifying potential risks. For each step of the lift, evaluate:

168.Severity (S): from 1 (minor) to 10 (catastrophic)

169.Occurrence (O): from 1 (unlikely) to 10 (frequent)

170.Detection (D): from 1 (certain) to 10 (impossible)

Criticality Index (CI) = S × O × D

A CI > 200 requires immediate corrective action. A CI > 100 requires a revision of the plan.

7.3 Human Factors

Human error is the leading cause of lifting accidents. To reduce errors:

Verify that the operator is certified and well-rested;

Ensure that signalers are trained and visible;

Establish a clear communication code before the lift;

Prohibit any alcohol or drug consumption;

Apply fatigue management: regular breaks, task rotation.

8. Pitfalls to Avoid

Here are the most frequent errors on the Red Seal exam on this topic:

183.Forgetting the 0.75 factor in multi-crane operations. The effective capacity is always 75% of the rated capacity, never 100%.

184.Confusing the included angle with the angle from vertical. The tension factor table uses the included angle (between the two slings), not the angle from vertical.

185.Neglecting the adhesion force for buried or submerged loads. It can represent 30 to 50% of the mass.

186.Using weight (lb) instead of mass (kg) in calculations. In Canada, loads are expressed in mass (kg) and forces in newtons (N).

187.Forgetting that the centre of gravity must be under the hook. If the CG is not aligned with the hook, the load will tip.

188.Ignoring minimum power line distances. The values of 3 m, 5 m, and 10 m are absolute minimums.

189.Not verifying ground bearing capacity. Uncompacted soil can give way under outriggers, even with a light load.

190.Confusing the standards. CSA Z150 applies to mobile cranes, CSA B167 applies to overhead cranes. Do not mix them up.

191.Forgetting the written lift plan for critical lifts. This is a mandatory requirement, not a recommendation.

192.Calculating sling tension without accounting for the weight of the rigging hardware (shackles, spreader bars, hooks). Their mass adds to the load.

9. Summary

A critical lift is classified as such based on relative mass, risk to personnel, load value, complexity, and environment.

Any multi-crane operation is automatically a critical lift and requires a written lift plan.

The effective capacity of each crane in a multi-crane operation is 75% of its rated capacity.

Load distribution between two cranes is inversely proportional to the distance between the CG and the attachment point of the other crane.

The included angle between two slings must never exceed 120°.

Minimum power line distances are 3 m (≤ 75 kV), 5 m (75–250 kV), and 10 m (> 250 kV).

The reference standards are CSA Z150 (mobile cranes) and the Mobile Crane Regulations (SOR/88-69).

Wind, ground bearing capacity, and dynamic forces must be integrated into capacity calculations.

A single lift director must direct any multi-crane operation.

Submerged or buried loads present an adhesion risk that can reach 50% of the mass.

The emergency plan and risk analysis (FMEA) are mandatory elements of planning.

10. Self-Assessment Questions

208.A load of 15,000 kg is lifted by two slings forming an included angle of 90°. What is the tension in each sling?

209.Two cranes lift a load of 30,000 kg. The CG is 1.5 m from crane A and 2.5 m from crane B. What load does each crane support?

210.A crane has a capacity of 40,000 kg at a radius of 8 m. In a multi-crane operation, what is its effective capacity?

211.An outrigger exerts a force of 250 kN on firm clay soil (bearing capacity 200 kPa). The load-spreading plate has an area of 1.5 m². Is the pressure acceptable?

212.What is the minimum distance to maintain from a 138 kV power line?

Answers: 1) 10,605 kg; 2) F_A = 18,750 kg, F_B = 11,250 kg; 3) 30,000 kg; 4) Pressure = 166.7 kPa < 200 kPa, acceptable; 5) 5 m.

Specialized Lifts, Multi-Crane Operations, and Critical Lifts