29 CFR Part 1630, Regulations to Implement the Equal Employment Provisions of the ADA (Title I Regulations with amendments issued through May 2016)

(r) Direct Threat means a significant risk of substantial harm to the health or safety of the individual or others that cannot be eliminated or reduced by reasonable accommodation. The determination that an individual poses a “direct threat” shall be based on an individualized assessment of the individual's present ability to safely perform the essential functions of the job. This assessment shall be based on a reasonable medical judgment that relies on the most current medical knowledge and/or on the best available objective evidence. In determining whether an individual would pose a direct threat, the factors to be considered include:

(1) The duration of the risk;

(2) The nature and severity of the potential harm;

(3) The likelihood that the potential harm will occur; and

(4) The imminence of the potential harm.