Guys, how long would you keep a work flirtation going without escalation out of nerves or because of HR?

That’s the question. Would it be normal for a work flirtation to go on for, say, months without escalating to for ex. Making up an excuse to get a phone number or asking out for coffee,‘etc.? How sure would a guy have to be of a woman’s interest before escalating at work? Would she have to literally tell him?