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Re: Fall Protection - Safety Factors

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I used to do a lot of this and if you are OSHA Qualified person, you can design the system for the actual anticipated loads with a minimum factor of safety of two.  I haven't check the OSHA regs in a long time but below is what I saved to justify the approach.  You can take the arresting force as 1800 lbs. as that is the limit that OSHA will allow on the body when you use a harness.  If you use a self retracting lanyard, I believe the force is limited to 900 lbs.
If you are a PE then OSHA will take you as a Qualified person as long as you are working in your competencies.

OSHA Regulations (Standards - 29 CFR)

1926.502.d.15 -- Anchorages used for attachment of personal fall arrest equipment shall be independent of any anchorage being used to support or suspend platforms and capable of supporting at least 5,000 pounds (22.2 kN) per employee attached, or shall be designed, installed, and used as follows:

(i) as part of a complete personal fall arrest system which maintains a safety factor of at least two; and

(ii) under the supervision of a qualified person.

1926.502.d.16 -- Personal fall arrest systems, when stopping a fall, shall:

(i) limit maximum arresting force on an employee to 900 pounds (4 kN) when used with a body belt;  [body belts no longer allowed for fall arrest]

(ii) limit maximum arresting force on an employee to 1,800 pounds (8 kN) when used with a body harness;

(iii) be rigged such that an employee can neither free fall more than 6 feet (1.8 m), nor contact any lower level;

(iv) bring an employee to a complete stop and limit maximum deceleration distance an employee travels to 3.5 feet (1.07 m); and, (v) have sufficient strength to withstand twice the potential impact energy of an employee free falling a distance of 6 feet (1.8 m), or the free fall distance permitted by the system, whichever is less.

Note: If the personal fall arrest system meets the criteria and protocols contained in Appendix C to subpart M, and if the system is being used by an employee having a combined person and tool weight of less than 310 pounds (140 kg), the system will be considered to be in compliance with the provisions of paragraph (d)(16) of this section. If the system is used by an employee having a combined tool and body weight of 310 pounds (140 kg) or more, then the employer must appropriately modify the criteria and protocols of the Appendix to provide proper protection for such heavier weights, or the system will not be deemed to be in compliance with the requirements of paragraph (d)(16) of this section.