When filming movie sex scenes, are the crew allowed to masturbate while filming?

Acting, directing, filming, recording and so on, in a sex scene isn't remotely erotic at all.  It's scripted, there are dozens of people all around doing their jobs. 

And it's not shot in one take - they film for about ten seconds, then stop, check the footage, make any necessary changes and then shoot those few seconds again or move on to the next section.  In between, they chat, have a laugh and a joke, eat a sandwich, have a cup of tea/coffee, read a book, do a crossword, etc.There's nothing sexy or a turn-on at all.

No, of course not.  I've heard actors say, there is nothing sexy about shooting those scenes.

Won't that cause them to drop the camera and microphone boom?

No, it might make the camera go shaky.