"Incumbent worker programs commonly include at least one of four testing triggers. Under 'reasonable cause' testing, an individual worker may be tested if her behavior reasonably gives rise to the suspicion of drug use. 'Comprehensive' testing involves the periodic, scheduled testing of all employees, such as during routine physical exams. 'Random' testing involves testing all employees (or particular groups of workers) on an unannounced and variable schedule (Hartwell et al., 1996). Finally, 'post-accident' drug testing (PADT) subjects any employee who reports a workplace accident (and sometimes co-workers who were directly involved) to a drug test at the time the report is made, regardless of whether the reporting worker’s conduct precipitated the incident."
Morantz, Alison D., & Mas, Alexandre, "Does Post-Accident Drug Testing Reduce Injuries? Evidence from a Large Retail Chain," American Law and Economics Review (Cary, NC: American Law and Economics Association, August 23, 2008) , Vol. 10, No. 2.