2The time of onset is generally a few minutes after decompression has

2 The time of onset is generally a few minutes after decompression has been completed, but may be delayed as much as 4 hours, occasionally a case may occur during decompression. Forms of compressed air illness 3 The different forms that compressed air illness may assume are very numerous, and any illness or unusual symptoms after compression should be investigated at once with a view to eliminating compressed air illness. 4 If any doubt exists, it is wise to place the person concerned under a small pressure to ascertain if there is any alleviation of the symptoms.