Intermittent Stabilization Anchor Systems
How do intermittent stabilization anchors work?
Intermittent Stabilization Anchors (ISAs) secures platform, or boatswain chair or seat board against the building facade to prevent the worker platforms from damaging the facade by high winds.
This is done with a lanyard attached from suspended platform rope to the building’s intermittent stabilization anchor with “quick connect” or detent pin. As the suspended platform descends, the workers stop to insert the “quick connect” pin to stabilize the platform. The pins may be inserted and removed at each level where the stabilization anchors are located. To maintain continuous stabilization as required at heights above 300 feet, the suspended platform must be roof rigged which is typically accomplished by roofed rigged davits (see roof rigged davit section for more information).
Are intermittent stabilization anchors necessary?
See how suspended platform performs in high winds when intermittent stabilization anchors are not used.
The Weather Channel Video of Suspended Platform caught in high winds:
Single Intermittent Stabilization System with Anchor in Curtain Wall Mullion
2. Permanent I.S.A. mounting block
3. Push button to detent the lock balls and remove/insert eye
4. Stage suspension cable
5. Connect lanyard from this eye to stage suspension cable
6. Lanyard lenght adjuster
7. Lanyard used to attach to the suspension should not configured to snag or bind
8. Removable eye/pin
Single, Intermittent Stabilization System with Anchor in Concrete
Is intermittent stabilization required?
Stabilization in some form is required for suspended work. While suction cups are commonly used by rope descent workers for positioning and stabilization by attaching to the building’s glazing, these devices can cause damage to the seals and worse. Therefore, stabilization should be part of the design process for suspended access, not an afterthought. See OSHA’s requirement for stabilization:
Stabilization is provided at the specific work location when the [rope] descent are greater than 130 (OSHA Subpart D. Section 1910.27 section (OSHA Subpart D. Section 1910.27 section (b)(2)(x)
[permanently installed swing stage] System utilizing angulated roping and building face rollers. The system shall keep the equipment in continuous contact with the building facade, and shall prevent sudden horizontal movement of the platform. This system is acceptable only where the suspended portion of the equipment in use does not exceed 130 feet (39.6 m) above a safe surface or ground level, and where the platform maintains no less than 10 pounds (44.4 n) angulation force on the building facade. (OSHA 1910.66(e)(2)(iii)(C)
If angulated roping is employed, tie-in guides required in paragraph (e)(2)(i) of this section may be eliminated for not more than 75 feet (22.9 m) of the uppermost elevation of the building, if infeasible due to exterior building design, provided an angulation force of at least 10 pounds (44.4 n) is maintained under all conditions of loading. (OSHA 1910.66(e)(2)(ii))
Supplementary information to OSHA Walking and Working Surfaces, on the subject of suction cups in subpart D, page 86:
Glass is a brittle material and, as such, can break without warning and vacate the window framing system. Glass installed in commercial and residential buildings is designed to withstand external loads, primarily wind events, with a certain safety factor. . . . In other words, breakage cannot be eliminated in brittle materials like glass. There is no way to guarantee a specific lite of glass will not break under the loads exerted by workers as they move vertically and horizontally back and forth across the glass lites. . . . The use of suction cups may be sufficient in certain conditions to cause the glass to break and vacate the opening, particularly in the event the RDS fails and the worker is left to rely upon the suction cups used for stabilization . . . to support his/her weight. View PDF of pages 85, 86, and 87
What are OSHA’s requirements for stabilization systems?
Typically, ISAs will be installed in pairs at the top of the building in-line with the support system above, e.g.: davit bases, rigging sleeves, and outriggers. The location can be either between the platform or just outside the suspension ropes, but, not both outside and inside the suspension ropes. The maximum vertical spacing for intermittent stabilization is 3-floors or 50 feet, whichever is less. See OSHA’s requirement for ISA systems below:
- “Intermittent stabilization system. The system shall keep the equipment in continuous contact with the building facade and shall prevent sudden horizontal movement of the platform. The system may be used together with continuous positive building guide systems using tie-in guides on the same building, provided the requirements for each system are met.” (OSHA 1910.66(e)(2)(iii)(A)(1)
- “The maximum vertical interval between building anchors shall be three floors or 50 feet (15.3 m), whichever is less.” (OSHA 1910.66(e)(2)(iii)(A)(1))
Intermittent Stabilization Anchors at two per floor vertically in-line
What is OSHA load requirements for ISAs?
Intermittent stabilization anchors must be capable of sustaining an ultimate design load of at least 600 pounds and 4 times the maximum anticipated load in any direction the load may be applied against facture of detachment. It’s worth considering designing above the minimum 600-pound ultimate strength because a swing stage could get hung-up on an ISA and cause damage to the facade that may be difficult to repair. See OSHA’s interpretation letter on ISA loading requirements as follows:
What is the ANSI Standard load requirements for ISAs?
“Building anchors shall be capable of sustaining without failure at least four times the maximum anticipated load to be applied or transmitted to the anchors. The ultimate design load for each anchor shall be a minimum of 600 lbs. (270 kg; 4:1 safety factor), applied laterally or perpendicularly.” (ASME A120.1-2014, Safety Requirements for Powered Platforms and Traveling Ladders and Gantries for Building Maintenance, sec. 220.127.116.11 Intermittent stabilization systems (b)”)