Well I always see it as more of a bargaining thing myself, the chemist wants some shit? Get him to make you a bottle of tricord for when someone gets unhappy and lights your office on fire.
Believe it or not, in most cases one good deed merits another, so by just giving service with a smile, you'll find by the end of the round, you can call in random favours from nearly any department at a whim.
Which is pretty much why that's what I've decided is Cargonia's Prime Directive. Supply the demand.
...Any thing else after that is fair game. You can go murder that Engineer to take back those 50 sheets of metal you just gave him. Whatever. The demand was satisfied, your job was done, and now you're as free as an Assistant without a boss.
Unless a head orders you to get something for them, in which case do it but very very slowly, and possibly have the muel send it somewheres obscure.
I don't see the point in delaying an order from a head. They're less useful for favours as there's less they can give you, but if they're happy to pick up the order themselves then there's no need to mess with them.
Well, when the person in question has no qualms about using grenades to blow up the Cargo Bay, I think it's all right to be a little hesitant in providing them with more.
So, you're using events that happened after the incident to justify your prior actions?
Honestly, what's a couple of large beakers to you? Nothing.
If you're loathe to give out grenade casings, then ask for CMO authorization. If you're REALLY loathe to do it then ask for specific purpose too.
I hate to point this out, but practically any sensible chemist will be able to acquire both of these things with no problems. Because they're
supposed to be making grenades. That's why they start with them.