4.3 Weather, Temperature and Ground Conditions

Environmental conditions change the demand

A rigging plan must account for weather, visibility, temperature, chemicals and supporting ground. These conditions can change forces, capacity or the ability to control movement. A rated load limit is based on specified conditions; it does not automatically apply to extreme heat, an incompatible chemical or a crane set over an underground void.

Wind affects both the suspended load and lifting equipment. A broad light panel can be difficult to control even when its weight uses little crane capacity. Gusts, projected area, orientation and the manufacturer’s limits all matter. There is no universal safe wind speed of 20 or 30 mph for every load. Use the approved equipment and load-specific limits, then stop when the conditions exceed them or control becomes inadequate.

For the same shape, orientation and aerodynamic coefficient in a simplified model, wind force varies approximately with the square of wind speed. Doubling speed from 10 to 20 units can multiply force by four. This is a relationship useful for understanding sensitivity, not a field design calculation or permission to use a generic coefficient for a delicate panel.

Visibility and precipitation

Fog, glare, darkness and heavy rain can prevent effective signaling or hide a hazard. Ice can affect load surfaces, sling flexibility, walking conditions and footing. Wind-blown dust can impair sight and contaminate moving mechanisms. The relevant question is whether the required observations and controls remain effective, not whether work has traditionally continued in similar weather.

Set weather monitoring and decision responsibility in the plan. If measured conditions differ between ground level and the load’s working elevation, address the controlling exposure. Avoid a universal instruction that one anemometer location proves conditions everywhere. The manufacturer or approved project method determines how the required monitoring is performed.

Temperature limits are material and assembly specific

OSHA 1910.184 and 1926.251 identify several sling-temperature restrictions. Fiber-core wire-rope slings exposed above 200°F must be permanently removed from service. For non-fiber-core wire rope used above 400°F or below −60°F, manufacturer recommendations apply. These requirements are not a general derating table for all steel-core sling assemblies.

For nylon and polyester web slings, OSHA prohibits use above 180°F. Polypropylene web slings have a separate 200°F restriction. A polymer’s melting point is not its permitted sling operating temperature. Damage or strength loss can occur well below melting, and fittings or protective components may introduce additional limits.

Alloy chain exposure also requires the applicable standard and manufacturer’s instructions. Under OSHA 1910.184, chain slings heated above 1,000°F must be permanently removed, and use above 600°F requires manufacturer-recommended capacity reductions. A particular chain grade or assembly may have stricter limits. Do not transfer a temperature chart from one grade, brand or fitting to another.

Chemical compatibility is not a color choice

OSHA prohibits nylon web slings where acids or phenolics are present. Polyester and polypropylene web slings cannot be used where caustics are present, and aluminum fittings have their own caustic restriction. A broad claim that polyester is “acid resistant” is insufficient to authorize a particular exposure. Consult the manufacturer for the actual substance and conditions.

Unknown exposure is a reason to remove affected gear from use pending evaluation. Discoloration, stiffness, embrittlement or burns may indicate damage, but absence of visible change does not prove chemical safety. Do not try to restore capacity with an improvised rinse, coating or field heat treatment.

Ground support is a system

For construction cranes, OSHA 1926.1402 addresses ground conditions and responsibilities, including the controlling entity’s preparation duties and information about known underground hazards. The operator and responsible personnel must establish suitable support for the actual configuration. A mat spreads load only to the extent that it has adequate rigidity, effective contact and supported bearing area.

A simplified area calculation divides a supplied support reaction by an approved allowable bearing pressure. If reaction is 80,000 lb and the given pressure is 2,000 lb/ft², the theoretical area is 40 ft². That calculation does not prove a 40-ft² timber panel works. Mat bending, soil layers, slope, voids and effective contact still require evaluation. Do not round a required dimension downward or invent a generic soil capacity from appearance.

Stop condition

During a trial lift, one support settles unexpectedly. Stop safely and return the load to a controlled supported condition. The movement may signal soil failure, a void or inadequate distribution. Continuing because the crane display remains below capacity ignores the support condition that makes its rating valid.

Sources: OSHA 1910.184, 1926.251, ground conditions.