Thank you for asking at HCM.
I went through your history and would like to reply you as follows:
1. Following can cause an asthma
b. Irritants in the air - dusts, smokes, air pollution, fumes, perfumes, etc etc
e. Some drugs such as Beta-blockers group, NSAIDs group (analgesics)
f. Psychological stress
2. From the above mentioned triggers, testing is available only for allergy causing substances. So I would suggest him allergy testing, which can help him identify the substances causing allergies.
3. If he is on any other long-term medications, please consult his doctor to know whether they can cause/trigger asthma attack.
4. Apart from avoiding the above triggers, I would suggest him regular breathing exercises which improve his lung capacity to benefit asthma.
Hope above suggestions will be helpful to him.
Should you have any further query, please feel free to ask at HCM.
Wish your father the best of the health.
Thank you & Regards.