Mean (±standard error) maximum daily PRISM temperatures on 2006–2021 HRI claims DOI and 5 days prior, stratified by: (A) whether or not claims occurred on cluster days; (B) whether or not claims occurred during the 2021 heat dome; (C) whether or not claims occurred on the first day (e.g., 7/11/2007, 7/28/2009, 6/27/2921) of a cluster. Error bars are ±standard errors. Workers were not directly observed on each day leading up to the DOI. DOI, day of illness (DOI - X denotes the DOI minus X days); HRI, heat-related illness; PRISM, parameter-elevation regressions on independent slopes model.