They must be honest and fair. Their active and personal participation is essential, because it demonstrates real concern and commitment. Find and help correct problems. Help conduct facility inspections. Assist in the determination of accident preventability.
Enforcement is always the job of supervisors and managers.
They are not a 'cure all' or a device that management can use to absolve themselves of doing anything more. Just as you shouldn't use a wrench as a hammer, management shouldn't use Safety Committees to do their job. Roles of Safety Committees should be clearly defined and constantly monitored to prevent disuse and abuse. Don't meet 4 times a year just to meet a quota. Don't quit trying.