Canada –
“…the province’s government-owned gas supplier, was called in the following day to investigate after the town became aware of the player’s symptoms.
There were deficiencies detected with two furnaces, so the arena was shut down…”
No mention of installed CO detection or the intent to install any.
Sask. rink carbon monoxide leak: Teens fall ill at tournament | CTV News

Faulty ice-cleaning machine blamed for carbon monoxide poisoning at Sask. hockey tournament

“The furnace was initially suspected to be the problem, but the Saskatchewan Health Authority said it was likely caused by a faulty ice-cleaning machine. It’s unclear whether the rink had a functioning carbon monoxide detector.”
Faulty ice-cleaning machine blamed for carbon monoxide poisoning at Sask. hockey tournament | CBC News