Can other trades work on a low sloped roof if they use a 6’feet warning line from the edge...

Fall Protection requirements for workers other than roofers, working on low-slope roofs.

Can other trades work on a low sloped roof if they use a 6’feet warning line from the edge and not have to be secured with safety harness or guard rails?

no.

OSHA’s fall protection for construction 29 CFR subpart M beginning at (1926.500), generally requires fall protection when there is a fall distance of 6 feet or more in a few, very specific situations low-slope roof work, some leading-edge work, precast concrete erection and residential construction; see 1926.501(b)(2)(12) and (13), because of feasibility limitations, the standard permits the use of a warning line, in combination with other measures, instead of conventional fall protection guardrail systems personal fall arrest systems or safety net systems to keep workers away from this edge. 

Installation of equipment, mechanical, electrical, plumbing does not fall within the categories listed; leading-edge work, precast concrete erection or residential construction.  Therefore, the warming line at the 6 foot option does not apply.

Where certain conditions are met, the use of a warning line 15 feet back from the edge will be considered by OSHA as a de minimis violation of the guard rail criteria in 1926.502 b.  The conditions that must be met for the application of OSHA is policy are as follows.

  1. A warning line is used 15 feet or more from the edge.
  2. The warning line meets or exceeds the requirements in 1926.502(f)(2).
  3. No work or work-related activity is to take place in the area between the warning line and the edge.
  4. The employer effectively implements a work role prohibiting the workers from going past the warning line with out safety harnesses or guard rails.

Therefore other trades, where these conditions are met, you may use a warning line 15 feet back from the edge to protect workers from a fall hazard.  If you have any questions contact Phil Mercuris, Vice President of Safety Services, Master Builders of Iowa 515-288-8904 / 515-250-7001 or 800-362-2578.