Because the practice of industrial hygiene encompasses such wide variety of knowledge areas, it was felt that, initially, there would need to be separate evaluations made of persons who restricted their practice to a narrow areas. Aspect examinations were created t certify a minimum standard of knowledge short of am comprehensive test of all areas. These aspect examinations have been dropped, except for that of analytical chemistry, in favor of a comprehensive evaluation of an applicant's knowledge. However, recently, a sub-specialty examination has been offered to provide a test of specific knowledge in the area of Indoor Environmental Quality (IEQ). It allows an already certified individual to demonstrate added depth of their knowledge in IEQ.

Because the tests evaluated technical knowledge and not actual practice, it was felt that some minimum time in actual performance of industrial hygiene duties would be essential for entry into the process. Therefore, a period of five (5) years experience is necessary before a person may take the examination. An intermediate level examination (a CORE examination) was developed to recognize persons who were undertaking this voluntary certification, but who did not yet have the five years experience, and to ensure that those testing in the former "aspects" maintained a core knowledge in all areas of practice. Also, an allowance was made for graduate education, recognizing the contribution that education has toward developing a mature practitioner. The contribution of education has been further recognized in that currently an appropriate Bachelor's Degree is required to qualify to take the examinations, and the ABIH is considering a requirement that a Master's Degree be a prerequisite for sitting for the examinations in the future.

However, rote knowledge is not the sole quality that identifies a competent Industrial Hygienist. There is an "art" to applying the technical principles in a manner that provides a reasonable solution for a workplace health issue. This is the real value behind the experience requirement for certification. A relationship with a practicing "Certified Industrial Hygienist" (CIH) is the key to learning the nuances in applying knowledge to work out the best solution. A "mentor" to show a new IH how to apply the book knowledge in the real world is valuable. Also, experience in as wide a practice as possible is imperative when you must demonstrate your knowledge in these sixteen rubics. This has become extremely difficult for "specialist" or those who practice in narrow areas. Limiting your experience to indoor environmental quality, or lead abatement, or confined spaces control can be a disadvantage when trying to demonstrate competency in other areas only know through a textbook or an " examination review course."