The science in all this is given below, corresponding to the respective individuals and situations.
A. One who has oil on his body: A person who has applied oil to his body; and has not taken bath has a high Raja component in his body.
B. One who has not washed his hands and mouth after eating: As the act of eating has just been performed and the hands and mouth are not washed as yet, his Raja component is in an increased state.
C. One who is clad in wet clothes: Less Sattva frequencies are emitted from such a person.
D. One who is ill: The Raja and Tama components in an ill person increase due to the illness.
E. One who has entered the ocean: A person who has entered the ocean is perpetually in danger. By doing namaskār to him we may also face the same danger.
F. One in despair: By doing namaskar to a person in despair, our mind can also be distracted and we may also experience despair. Also it is generally incorrect to do namaskar to a person in despair.
G. One carrying a load: The Raja component is predominant in a person carrying a load. Also doing namaskar to him will amount to keeping his (unnecessary) role model of carrying a load.
Courtesy: Forum for hindu awakening