“Small business” means a corporation or a concern, including its affiliates, that is independently owned and operated, not dominant in its field, and employs fewer than 50 full-time employees or has gross annual sales of less than $4,000,000. For purposes of a specific rule, an agency may define small business to include employment of 50 or more persons if it finds that such a definition is necessary to adapt the rule to the needs and problems of small businesses and organizations.