The Director may grant a temporary or permanent variance from a State occupational safety and health standard upon application by a public employer to the Director. The Director may grant a variance from a standard or portion of a standard if the Director determines that the variance is necessary to permit an employer to participate in an experiment approved by the Director designed to demonstrate or validate new and improved techniques to safeguard the health or safety of workers. A variance from a State occupational safety and health standard may only have future effect.