In lifting operations, precision and safety are inseparable. Every hook, rope, and hoist is designed not only to carry a load, but to do so safely within strict margins. These margins are defined by something fundamental to all mechanical design: the factor of safety (FoS).
The factor of safety determines how much stronger a component must be than the maximum load it is expected to carry. For RGM Cranes, it’s a principle built into every product – ensuring that overhead cranes, hoists, and lifting accessories perform safely and predictably, even in demanding conditions.
What Is a Factor of Safety?
In simple terms, the factor of safety is the ratio between the minimum breaking load (MBL) and the working load limit (WLL) of a lifting device.
For example, if a chain sling has a breaking strength of 50 tonnes and a safety factor of 5:1, it will have a WLL of 10 tonnes. That means the equipment is designed to hold five times its rated capacity before it reaches the point of failure.
The FoS exists because real-world conditions are rarely perfect. Wear, fatigue, shock loading, and environmental stress can all reduce the effective strength of a component. The safety factor provides the engineering buffer that accounts for those uncertainties.
Working Load Limit vs. Breaking Strength
A frequent point of confusion in lifting safety is the difference between a working load limit and a breaking strength.
- Breaking strength is a laboratory value – the point at which a component will physically fail under a static test.
- Working load limit (WLL) is the maximum load that can be safely lifted in service, taking into account the specified factor of safety.
Exceeding the WLL doesn’t just risk damage; it shortens service life and increases the likelihood of catastrophic failure. Respecting the WLL means working within the design’s safety envelope – not testing its limits.
Typical Safety Factors in Lifting Equipment
Different lifting devices are designed with different safety margins depending on their function and applicable standards.
- Chain hoists and blocks: 4:1 to 5:1
- Wire ropes and slings: 5:1 to 6:1
- Shackles and hooks: around 6:1
- Man-riding or personnel hoists: 10:1 (because no margin is too great when lives are at stake)
These ratios are guided by international and regional standards, including SANS 10375 and the Driven Machinery Regulations in South Africa, or LOLER 1998, BS EN 13155, and HSE Hoisting Guidelines in the UK. Regardless of jurisdiction, the intent is the same: to make sure that lifting equipment is always stronger than it needs to be.
Why the Factor of Safety Isn’t Over-Engineering
A common misconception is that high safety factors mean unnecessary bulk or cost. In reality, they’re about predictable performance — ensuring that even under shock loads, heat, vibration, or misuse, the equipment remains within a safe operating range.
Modern manufacturers like RGM balance safety and efficiency using advanced materials, fatigue modelling, and precision fabrication — creating equipment that’s both strong and smartly engineered.
Conclusion
Safety factors are the invisible safeguard behind every successful lift. They represent the discipline of engineering over assumption: the difference between working safely and working on borrowed time.
Understanding how the factor of safety, working load limit, and breaking strength interact is essential for anyone responsible for overhead lifting. Because in the world of cranes and hoists, true safety isn’t a product feature; it’s built into the design from the very first calculation.
