I'm driving, stopped at a red light and in the left turn lane. A fire engine comes up behind me, siren blaring, lights flashing, pulls behind me and lays on the horn. What do I do?

Title says it all.

While this has not happened to me I have a fire station not far from me and I see this rather often. Someone is at an intersection and in the fire engine’s way and the fire engine driver lays on the horn big time. The person in front does not know how to get out of the way so sits there paralyzed all the while the fire engine driver is honking his (very, very loud) horn.

What is the proper action for the driver of the car in the way?

Do what the fire truck would do if you weren’t there. Look around carefully, and as soon as it’s safe to do so ignore the red light and make your turn. (Then pull to the side, obviously.)

Same applies if you’re in any lane at a red light and the fire truck has no way around you. Check for traffic, then pull through the junction, then pull over.

And if you are (say) third in line in the left turn lane just hope everyone gets the message?

If the car in front of the fire engine is boxed in they shouldn’t do anything but wait until they aren’t boxed in so you must be asking something else. Are they waiting for a light to turn green or for traffic to pass? They can certainly get out of the way of the fire truck if it’s safe to do so.

I’ve been in that boxed in condition for 20 minutes with an ambulance blasting a horn right behind me even though there were at least 10 cars ahead of me jammed into this weird intersection with the cross street ahead packed with traffic that wasn’t letting anyone out.

I see this happen a few times a week. Take your pick. Car is at a red light. Other cars are in front. Traffic is coming from other directions.

Makes no matter to the fire truck driver who just happily toots his horn.

You’ll have to clarify what you mean. If you’re boxed in obviously you cannot do anything. And if the lane to your right is empty, the fire truck would surely use it.

Well obviously the fire truck is not honking at the boxed-in car immediately in front expecting him to dematerialize, he’s sounding his horn to tell the car at the front of the line to ignore the red light (when safe) and pull through the junction and out of the way. Other cars and then the fire truck would follow.

Yeah, if the fire engine can drive around traffic they do so.

Get out of the way as quickly as possible, but that may mean crawling slowly into the intersection to assert yourself. When I lived in Dallas, fire trucks would drive down the wrong side of the road (against multiple lanes of oncoming traffic) if necessary. Other drivers ought to hear the blaring siren and realize everybody yields to emergency vehicles.

I mean, it just seems like common sense to me that the fire truck is implicitly authorizing you to ignore the red light when safe to pull through the junction and get out of the way.

It would not surprise me, however, if a lawyer is driving the car that he might decide he has no personal liability from sitting where he is until the light turns green, but that he might have potential liability if a road accident ensued.

Can you turn left on a red in the US?

Of course not.

Well, you may be able to do so, from a one-way street onto another one-way street.

Do fire engine drivers have the legal authority to tell a driver in a car to break the law?

Well, that’s what you just recommended. The thread title is "stopped at a red light in the left turn lane. You said, “as soon as it’s safe to do so ignore the red light and make your turn” So you’re saying that you can turn left on a red light.

A firetruck can. If I were preventing the firetruck from doing so, then I would safely proceed through the red light. I’m pretty sure I’ve done this at least twice.

I’m saying if I were confident that it were safe to do so I would ignore the red light rather than let people burn, yes. If a cop ticketed me for it I’d leave it up to the judge. If it’s technically illegal it would make no difference to what I would do, so I don’t particularly care about the legality of it.

In the situation described in the OP, there are extenuating circumstances.

Yes, the emergency vehicle is the ace of trump, full stop.

Yes, they do. Here in Arizona all emergency vehicles have the right of way by law. That means if you’re waiting for a green light, you should move out of the way of the emergency vehicle as soon as it is safe to do so, regardless of the light’s color.

In Tucson, this scenario is rare, however. The traffic lights are fitted with sensors that are activated by a strobe light on the vehicle and turn the lights to green in favor of the emergency vehicle and the lights to red for cross traffic.