By increasing your knowledge and gaining experience. Forwarding effective recommendations to management is crucial if credibility is to be gained. Find out who has the ear of the CEO, and you find who has position power. The safety committee has the most position power when the Chairperson regularly meets with the person at the top who is making the decisions for the workplace. Communication is the key here.
Employees see the safety committee as a communications conduit to management.
When an employee informs or makes a suggestion to the safety committee representative, he or she expects to get some sort of feedback soon thereafter. They want to see action. Therefore, to gain credibility with employees, communicate regularly and often with them. If a hazard can't be fixed for a while, let the workers know the what's and why's behind the delay. They will appreciate it, even if it's not the answer they want to hear.