A request for help about prime health hazard (8)

I believe the answer is:

asbestos

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'health hazard' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

'a request for help about prime' is the wordplay.
'request for help' becomes 'sos' (I've seen this in another clue).
'about' is an insertion indicator.
'prime' becomes 'best'.
'sos' placed around 'best' is 'sbestos'.
'a'+'sbestos'='ASBESTOS'

Can you help me to learn more?

(Other definitions for asbestos that I've seen before include "retardant" , "Old fire-retardant" , "fire protection" , "risky material" , "'Fireproof substance, dangerous to health (8)'" .)

I've seen this clue in The Times and The Sunday Times.

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