There are two types of psychiatric commitments -- voluntary and involuntary. During a voluntary commitment, the patient agrees they are having a mental health problem that is serious and consents to an evaluation in a psychiatric ward. Many people with mental health problems do not realise that they are ill however, and commitment against the patient's free-will must be considered. Although rules differ, in most states, at least three mental health professionals -- including one medical doctor -- have to agree that the patient is a threat to himself or others for an involuntary commitment to be pursued.
Convince the patient that they should see a doctor for evaluation. This can be conducted on an outpatient basis, but it is also commonly done after-hours in an emergency room.
If you have difficulty reasoning with them, use the least restrictive method to get them to comply. If they believe that Martians are invading the earth, for example, ask them if they would like to talk to the authorities to share what they know. Then, bring them to see the doctor.
You cannot physically force them. If the patient is threatening to hurt himself or others, you can call the police, who will transport the patient to an emergency room for evaluation.
Tell the doctor evaluating the patient about any specific threats made against others.
To meet the criteria for involuntary commitment, the threats have to be specific to a person and intent.
The statement: "I am so mad I could kill someone," does not meet the specificity requirement for either person or intent.
The statement: "I am so mad I could kill my boss," meets the person-specific requirement, but not the requirement with regard to intent.
The statement: "I am going to stab my boss" meets the requirements for specificity of both person and intent.
Note any recent comments the patient has made about harming herself. Again, the comments must be specific with regard to intent.
If the patient says: "I wish I could blow myself up," this statement does not meet the specificity for intent -- unless she has a bomb.
If the patient says she is going to cut herself, this statement qualifies, because it is realistic that she could carry out this threat.
Tell the doctor about any history of life-threatening behaviour. Include everything the patient has done in the past that is dangerous. Behaviours such as spending all of his money, being delusional or drinking a lot, do not necessarily meet the criteria to be considered life-threatening; although they certainly are self-destructive and possibly harmful to others: Behaviors such as setting fires or trying to jump off of a high building however, meet the criteria.
In most states, the person can only be held for psychiatric evaluation for 72-hours whereupon the criteria for commitment is reviewed by a judge.