I've heard it said that once a second employer arrives on site, with just one employee, the accident risk factor for everyone on site just went up by as much as 40 percent.

In reality, budget and schedule often supersede safety concerns. On the multi-employer construction sites I've audited, hazard communication is Spartan within any one company and all but non-existent between prime and subcontractors. There might be weekly job meetings scheduled, but attendance is usually weak across the board. Few, if any, cross-contract safety issues are thoroughly reviewed and resolved in detail. It just seems that the written, site-specific safety and emergency action plans for every contractor are far from a project-wide reality. Everyone admits to gaps in safety policies, but no one takes the time or expense to upgrade policy, purchase equipment or train personnel to correct the deficiencies.