Definition of Reasonable Diligence as stated in 1910.1096(d)(1).

April 17, 1991

The Honorable John McCain
United States Senate
[Recipient address omitted]
Dear Senator McCain:

This is in further response to your letter of February 11, to the Occupational Safety and Health Administration (OSHA) concerning radon.

My letter of January 17, to Mr. Craig I. Willison of American Radon Corporation, related that an employer must conduct the survey described at 29 CFR 1910.1096(d)(1) of the ionizing radiation standard if he or she knows, or could have known with the exercise of reasonable diligence, of the existence of artificially enhanced concentrations of environmental radon-222 in the workplace. You seek a clarification of the term "reasonable diligence" in relation to knowledge of the existence of artificially enhanced concentrations of environmental radon-222. You described a theoretical situation in which ten percent of the structures surveyed in an Environmental Protection Agency (EPA) study area were found to exceed the radon standard, and inquired whether the exercise of "reasonable diligence" would lead an employer to conduct a survey to determine concentrations of radon in his or her workplace. Additionally, you inquired as to what incidence of radon found in surrounding buildings would trigger the exercise of "reasonable diligence" on the part of the employer, if ten percent was not the threshold requirement.

The answer to your question concerning the definition of "reasonable diligence" depends upon facts specific to each individual case. In this case, OSHA's definition would not be based solely on the percent of structures found to contain levels of radon exceeding the standard. However, given a situation in which an employer is provided with a copy of the referenced EPA report, it could be argued that knowledge of this incidence of radon, plus the fact that his workplace is within the confines of the geographical area surveyed, could give rise to a duty to test, or at a minimum, to make further inquiry. In addition, an employer could know of a potential hazard with the exercise of reasonable diligence if the media has reported excessive radon exposure in the area where the workplace is located.

We appreciate the opportunity to clarify this matter for you.

Sincerely,

Gerard F. Scannell
Assistant Secretary

[Requester letter reproduced on OSHA page; omitted here.]