Are there any circumstances where I can refuse to hire an individual because of his/her disability?

An employer is not required to hire or retain a candidate or employee posing a "direct threat" to the health and safety of co-workers or themselves. The job must pose an imminent and substantial degree of risk. Still, the employer must first engage in the interactive process to determine if there is any reasonable accommodation that would allow the candidate or employee to perform the job without endangering his or her health or safety, or the health or safety of others or without causing undue hardship. There is a heavy burden of proof on the employer that rejects an employee because of an alleged direct threat to his or her own health or safety.