Rigging Hardware, Slinging, and Load Control

Rigging Hardware, Rigging, and Load Control

Introduction

This chapter covers all the knowledge required for the Red Seal exam concerning rigging hardware, rigging techniques, and load control. Mastering these concepts is essential: the majority of incidents in mobile crane operations occur during rigging or lifting, not during travel. You must know the applicable Canadian standards, load factors, failure modes, and inspection procedures.

1. Slings: Types, Construction, and Selection Criteria

1.1 Wire Rope Slings

Wire rope slings are composed of strands wrapped around a core (fibre or steel). The strength depends on the configuration factor (CF) that applies according to the rigging mode.

Fundamental formula:

Working Load Limit (WLL) = Minimum Breaking Load (MBL) ÷ Safety Factor (SF)

For wire rope slings, the safety factor is 5 according to CSA Z150 (Safety Code for Mobile Cranes).

Table 1 — Configuration Factors for Wire Rope Slings

Caution: the configuration factor applies to the working load limit, not to the breaking load. A frequent error is multiplying the MBL by the CF — this is incorrect.

1.2 Synthetic Web Slings (Textiles)

Synthetic web slings are made of polyester, nylon, or polypropylene. Polyester is the most common because it resists acids and abrasion well. Nylon resists alkalis but loses 10 to 15% of its strength when wet. Polypropylene is lightweight and floats, but degrades under UV exposure.

Configuration Factors for Web Slings:

Important note: for web slings, the safety factor is 7 (standard CSA Z150). The sling's label indicates the working load limit for each mode; if the label is illegible or missing, the sling must be removed from service.

1.3 Chain Slings

Chains are used for abrasive, high-temperature, or cutting loads. Their safety factor is 4 according to CSA Z150. Grade 80 (T) and grade 100 (V) chains are the most common in crane service.

Table 2 — Common Diameters and Working Loads (Grade 80)

Chain Inspection: measure wear at the contact point between links. If the diameter reduction exceeds 10%, the chain must be removed. Also check for elongation: a link stretched more than 5% from its original length indicates plastic deformation.

2. Rigging Hardware

2.1 Shackles

Shackles are classified by type: screw pin shackles and safety bolt shackles. The working load limit is stamped on the body. The safety factor is 5 for shackles conforming to CSA B167 (standard on lifting accessories).

Usage Rules:

2.2 Hooks

Lifting hooks must be equipped with a functional safety latch. Removal-from-service criteria include:

2.3 Rings and Swivels

Master links and swivels must be inspected for wear, corrosion, and cracks. A swivel that no longer rotates freely must be removed from service.

2.4 Sheaves and Blocks

The sheave must have a minimum diameter of 18 times the rope diameter for 6 × 19 rope, and 21 times for 6 × 36 rope (CSA Z150). A sheave diameter that is too small causes accelerated rope fatigue.

3. Rigging Techniques

3.1 Rigging Modes and Angles

The rigging angle is the angle formed between the sling leg and the vertical. The greater this angle, the higher the tension in each leg.

Formula for calculating tension per leg:

T = (P ÷ N) × (1 ÷ cos Ω)

Where:

Table 3 — Tension Multiplier by Angle

Rule of thumb: the angle between two legs of the same sling must never exceed 90° (i.e., 45° from the vertical). Beyond this, the working load limit is reduced disproportionately and the risk of failure increases.

3.2 Basket Hitch

The basket hitch distributes the load over two legs. The configuration factor is 0.7 per leg for wire rope. The load must be centered; if the load is off-center, each leg supports an unequal load and the calculation must be redone with the maximum load on a single leg.

3.3 Choke Hitch

The choke hitch grips the load. The configuration factor is 0.75 for wire rope and 0.80 for web slings. The choke angle (angle between the two parts of the sling at the contact point with the load) must not exceed 120°. Beyond this, the load may slip and the sling may deform.

Golden rule: the choke point (the knot) must always be positioned on the load, never on the hook.

3.4 Multi-Leg Rigging with 3 and 4 Legs

For 3 legs: configuration factor = 2.1 (wire rope). For 4 legs: factor = 2.8. Important: these factors assume the load is rigid and all legs are tensioned equally. In practice, with a flexible load or uneven ground, a single leg may support most of the load. The prudent rule is to consider that only 2 out of 4 legs support the load under real conditions.

4. Load Calculations and Centre of Gravity

4.1 Determining Load Weight

The weight must be known before any lift. Sources include: drawings, invoices, weighings, or calculating volume × density.

Table 4 — Common Densities (kg/m³)

Calculation example: a steel beam measuring 6 m × 0.3 m × 0.5 m has a volume of 0.9 m³. Weight = 0.9 × 7,850 = 7,065 kg.

4.2 Centre of Gravity (CG)

The centre of gravity is the point where the total mass of the load is concentrated. For a stable lift, the hook must be directly above the centre of gravity. If the CG is offset, the load will tilt until the CG is under the attachment point.

Method for calculating the CG of a composite load:

Total CG = (Σ (weightᵢ × distanceᵢ)) ÷ Σ weightᵢ

Where distanceᵢ is measured from an arbitrary reference point.

Trap to avoid: for a load with an unknown CG, perform a test lift of 150 mm maximum, check the balance, then adjust the attachment points before continuing.

4.3 Safety Margin and Load Factor

The working load limit (WLL) of an accessory is the maximum load it can support under normal conditions. The proof load is generally 1.25 × WLL. The breaking load is the point of failure. The safety factor is the ratio between the breaking load and the WLL.

Table 5 — Safety Factors by Accessory Type (CSA Z150)

5. Inspection and Removal from Service

5.1 Inspection Frequency

5.2 Removal-from-Service Criteria — Wire Rope

According to CSA Z150, a rope must be removed if:

5.3 Removal Criteria — Synthetic Web Slings

5.4 Removal Criteria — Chains

6. Load Control During Lifting

6.1 Stability and Sway

Load sway is a major hazard. Causes include: improperly positioned CG, excessive wind, sudden acceleration or deceleration, or abrupt braking. The operator must:

6.2 Communication and Signals

Communication between the operator and the signaler (rigger) is essential. Standardized hand signals are defined in CSA Z150. In the event of loss of communication, the operator must stop all movement immediately and hold the load in a stable position.

6.3 Lifting Loads in Wind

The maximum wind speed for a lift depends on the exposed surface area of the load and the manufacturer's specifications. As a general rule, wind exceeding 32 km/h (20 mph) requires increased caution. Beyond 48 km/h, lifting must be stopped, unless the manufacturer indicates a higher limit.

6.4 Submerged or Frozen Loads

A partially submerged or frozen load presents a risk of load surprise: the force required to break it free is greater than its apparent weight. The operator must:

7. Safety Rules and Applicable Standards

7.1 Relevant Canadian Standards

7.2 Golden Rules of Rigging

7.3 Operator Responsibilities

The mobile crane operator is responsible for:

8. Traps to Avoid

9. Summary

10. Self-Assessment Questions

This chapter covers the essential theoretical and practical knowledge for the Red Seal exam in mobile crane operation. Mastering the calculations, factors, and inspection criteria is essential. Review the factor tables, removal thresholds, and safety rules until they become automatic. Good luck with your preparation.