BMI level for men which is considered as lethal is:
Ref. Foundations of Community medicine. Page. 293
 
Body mass index (BMI) is an estimate of total body fat mass

Simply an index of weight for height.

● Formula: Weight in kilograms divided by the square of height in meters.
● Uses:

Body mass index = Weight (kg)/(Height)2 (m)
Used to classify and define underweight, overweight & obesity in adults.
BMI value considered lethal for Men is 13 and for female is 11
11
13
12
15