[lessnonymous]

(Ignoring all the safety stuff in other replies)

These are tunnels over 3km long. You can't have cops down there without breathing apparatus - even if the extractors were safely operating.

[ghshephard]

Why would it be safe for people driving vehicles, but not for police officers?

[DrStalker]

In a vaguely sealed container with air being supplied through filters for a few minutes vs. standing in the fumes directly for hours.