The scheme will permit safety representatives, including union officials, to visit sites to check on safety records.
But Suzannah Nichol, the confederation's health and safety director, said it was not persuaded of the value of the pilot. She said there were better ways to involve workers in health and safety.
She claimed the trial scheme was flawed, crucially because there was no way to measure if health and safety standards had improved as a result of the pilot.
She said: "Safety representatives who move from site to site cannot build up relationships with managers and the workforce in the same way as site-based reps."
Nichol said the confederation would follow the progress of the trial and would re-examine the scheme's merits if fundamental changes were made.
It is understood that the pilot schemes were to have been launched late this month but they are now set to begin early in the new year.