I read that in the cannon scene where Keaton used too light a charge, the shot squibbed and landed in the engineer's cab, alongside of him. The commenter noted that it was an actual charge, and if it had been miscalculated, the ball would have killed Keaton. (no actors' unions in those days).
I groaned though, when the bridge collapsed and wrecked that great looking locomotive. And, in those pre-CGI days, they used one Helluva lot of extras with 45-70 breechloaders (current price $1,000).
In the scene where he gets water for the engine and it knocks him down he broke his neck on the rail. He kept on working to finish the film. He didn’t find out until several years later when he had an x-ray done.