1. Safety requirements for confined spaces;American National Standards Institute,1989
2. Epi Info computer programs for epidemiology;Centers for Disease Control. (CDC),1988
3. Standard Industrial Classification Manual;Executive Office of the President, Office of Mangement and Budget,1987
4. Mathematical Evaluation of Controlling Hazards;Fine,1980
5. Criteria for a recommended standard;National Institute for Occupational Safety and Health,1979