It's not as simple as Severe Mental Impairment. It's a quadruple test. It's a test of all of the following criteria (if one fails, the whole claim fails):
Severe Mental Impairment
and
Severe Impairment of Social Functioning
and
Severe Behavioural Problems
and
In receipt of High Rate Care.
SMI: ADHD is specifically excluded in the Decision Makers' Guide:
"61359 It is not possible with the current state of medical knowledge to attribute the condition attention deficit hyperactivity disorder (commonly known as ADHD) to a state of arrested development or incomplete physical development of the brain within the meaning of the regulation.
1 SS (DLA) Regs, reg 12(5)
61360 In cases involving attention deficit hyperactivity disorder, the DM should make sure that the person has no other disability which could satisfy the severely mentally impaired test. Difficult cases should be referred to Medical Services for advice." pg. 57
The SMI bar is set high. In IQ terms it would be an IQ of 55 or less. IQ is not necessarily the determination, though:
"The DM should consider whether there
- is difficulty with communication so that
1.1 speech may be severely impaired, often only monosyllabic or grunting noises or
1.2 reading or writing skills may be absent or very poor or
- are severe learning difficulties or
- is a lack of understanding of everyday living.
People with severe impairment of intelligence are likely to need specialized schooling, and supervision of all activities. In cases of doubt and where the IQ is over 55 the DM should refer the case to Medical Services for expert advice." Pg. 58
Severe Impairment of Social Function is set similarly high:
"some people who have a low intelligence can relate to other
people and perform basic social skills once they are shown how to do them. But others who have a low intelligence are not able to perform basic tasks or relate to others. It is the latter who would display severe impairment of intelligence and social functioning." p.59
Severe Behavioural Problems is set extremely high:
"61376 People are treated as having severe behavioural problems if they exhibit disruptive behaviour that
- is extreme and
- regularly requires another person to intervene and physically restrain them
2.1 to prevent them injuring themselves or others or
2.2 damaging property and
- is so unpredictable that they require another person to be present watching over them whenever they are awake.
It is essential that all three conditions are satisfied. The disruptive behaviour does not need to be displayed at all times but it must be extreme. The word “extreme” is an ordinary English word which here refers to behaviour which is wholly out of the ordinary." p. 59
"61379 The claimant’s behaviour must be so destructive and unpredictable that they require the presence of another person to watch over them whenever they are awake. This is in all aspects of the claimant’s life both indoors and out. If a claimant displays
behavioural problems at home but elsewhere, for example at school, is well behaved then the test will not be satisfied." p. 61
It's a very, very hard test, and no sense of danger is not sufficient to pass it.