In cases like this it's worth brainstorming a bit first. After and during it might be a good idea to see what others have done with tools like the noun project (and search for broken and crane for example). Then just integrate the ideas by combining things, here I'm combing crane, broken bone and typical warning sign. YMMV.
Image 1: Quick example combining 3 different concepts
Obviously you need to do your own thinking here and my example is very quick but shows how you could approach the problem.
Maybe display a broken crane, like you would display a broken heart? Or a large bandaid icon, accompanied with a word/text?
If you can use colours I'd say make a green crane for OK, a red one (optionally with a line through it) for forbidden and a grey one for 'not available'.