The most common and most likely answer to this crossword clue is the 5 letter word RADON
I've seen this crossword clue in The Daily Telegraph
R
A
D
O
N
More clues leading to the result RADON
- Gas attack announced, and taking place
- Controlled squeezes make gas
- Bolted boxes gathering gas
- Managed to suppress party as a health hazard
- . Gas managed to overwhelm cook
- Managed to cook – bottled gas
- Retrospective acknowledgement: argon is noble gas
- Right bit of trouble with northern element
- Gunners tacitly agree to lift unhealthy gas
- Foul and/or noxious gas
Buddy explains!
The straight part
We know that "Dangerous element" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dangerous element = radon.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RADON mean?
RADON noun- The chemical element (symbol Rn, formerly Ro) with atomic number 86. It is an odorless, colorless, chemically inert but radioactive noble gas.