Scaffold Per-Leg Load and OSHA 4:1 Check
The load on each scaffold leg and whether it clears the OSHA 4:1 safe working load.
Example
You enter
- Platform + scaffold dead load in the bay (lb) 100
- Workers on the bay (count) 2
- Weight per worker with tools (lb) 250
- Stored material load (lb) 500
- Legs sharing the bay (count) 4
- Leg / frame ULTIMATE capacity (lb; a published ALLOWABLE leg load already includes 4:1 -- enter 4x it) 2500
You get
- Total load (lb) 1100
- Load per leg 275 lb (OK)
- Swl (lb) 625
- Utilization 0.41
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
Scopetotal = platform dead + workers x 250 lb + material; leg load = total / legs; OSHA asks the leg to carry its own share of the dead load plus 4 x the intended (workers and material) load, against its ULTIMATE capacity (a published allowable load already has the 4:1 in it). A bay with two workers, 500 lb of material, and a 100 lb platform puts 275 lb on each of four legs - 41% of a 2,500 lb capacity, but load it heavier and it crosses the 4:1 line. Feeds the mudsill bearing check; a competent person verifies.
Formula or tabletotal_load_lb = platform_dead_lb + num_workers x worker_lb + material_lb; leg_load_lb = total_load_lb / n_legs; swl_lb = component_rating_lb / 4; utilization = (platform_dead_lb / n_legs + 4 x intended load per leg) / component_rating_lb (component_rating_lb is the ULTIMATE capacity); pass = utilization <= 1.
Source and editionOSHA capacity rule by name (safe working load = rating / 4; leg load = total intended load / legs); first-principles load distribution.
Free accessThe 4:1 rule and 250-lb-per-person basis are public OSHA requirements; the component rating comes from the manufacturer.
What governsEstimate. AHJ and licensed professional govern.
API field namesplatform_dead_lb, num_workers, worker_lb, material_lb, n_legs, component_rating_lb, total_load_lb, leg_load_lb, swl_lb, utilization
- Intended load 250 lb per worker (with tools) + stored material; the platform/scaffold dead load is carried at 1x, not 4xOSHA 1926.451(a)(1); OSHA interpretation 2013-12-06
- Capacity check dead load per leg + 4 x intended load per leg <= the component's ultimate capacity, shared evenly over the legsOSHA 1926.451(a)(1) / manufacturer