What 29 CFR 1904.5 requires (plain English)
29 CFR 1904.5 supplies the first prong of the recordability test in §1904.4, whether a case is work-related. The standard sets a broad "geographic presumption": an injury or illness is work-related if an event or exposure in the work environment either caused or contributed to it, or significantly aggravated a pre-existing injury or illness, and work-relatedness is presumed for conditions resulting from events or exposures in the work environment.
That presumption is rebutted only by the specific, closed list of exceptions in §1904.5(b)(2): for example, injuries at the workplace solely from eating or drinking one's own food, from personal grooming or self-medication, from voluntary participation in a wellness program, from a personal task outside working hours, or symptoms surfacing at work but resulting solely from a non-work event. If no listed exception fits, the case is work-related.
"Work environment" is defined broadly: the establishment and other locations where employees work as a condition of employment. Because the presumption favors recording and the exceptions are narrow and specific, most cases that occur at work are work-related, and employers must be able to point to a listed exception, not a general belief that a case was "personal."