What is the capacity of the lifeline? How many posts do I need for a 60' system?

Good Afternoon, 

The capacity of single span systems is two persons. The capacity of multiple span systems is two persons secured on each span with a maximum of six people installed on the system. The maximum weight of each person, including tools and clothing, is 310 lbs (141 kg). See below link for Instructions. 

You can also call 3M for additional assistance at 1-888-3M-HELPS. 

https://multimedia.3m.com/mws/media/1420668O/dbi-sala-securaspan-horiz-lifeline-system-i-beam-stanchion-ui.pdf&fn=IFU_5903032_SecuraSpan_HLL_Steel_Beam_EN.pdf

Thank you