OSHA and its lawyers have for years cited the NWS heat index chart as evidence that employers exposed their employees to excessive levels of heat, in violation of the OSH Act’s catch-all provision, the General Duty Clause.
In 2016 and 2017, OSHA issued five such citations to the United States Postal Service (USPS), alleging violations in San Antonia and Houston, Texas; Des Moines, Iowa; Charleston, West Virginia; and Benton, Arkansas. OSHA introduced the NWS heat index chart into the trial record and pointed to it as evidence.
USPS argued, however, that the chart’s second layer should be disregarded as lacking a scientific basis. (Ogletree Deakins represented USPS in this matter.) It argued that the NWS had based the chart’s second layer on a 1981 article in a popular magazine on weather and climate. The article cited, however, no sources for its assertions that certain heat index values indicated caution, extreme caution, danger, and extreme danger. USPS also showed that the co-authors of the article were a meteorologist and a climatologist with no apparent qualifications in human physiology. It also introduced expert testimony rebutting the idea that the chart had any scientific validity.