A carbon monoxide leak is very unlikely to explode. While theoretically, it's possible that it could build up in an enclosed space without catching fire, the odds are overwhelmingly in favor of it catching fire long before it explodes.

Can you ignite carbon monoxide?

Carbon monoxide is a colorless, odorless gas. Prolonged exposure to carbon monoxide rich atmospheres may be fatal. It is easily ignited. It is just lighter than air and a flame can flash back to the source of leak very easily.

Is carbon monoxide highly explosive?

Flammable Properties: EXTREMELY FLAMMABLE GAS. ... Explosive rupture and a sudden release of large amounts of gas may result. Cylinder may rocket. In a fire, the following hazardous materials may be generated: Very toxic carbon monoxide, carbon dioxide.