The pulse duration is so small I wouldn't worry about it. Probably a 15A relay would suffice; these are typical currents for mains inrush for example (which is 1/2 or 1 or several cycles at mains frequency -- much longer duration), and comparable to normal (lightning induced) surge but usually not quite as long (that'd be more like a telecom 10/1000us pulse, but that isn't usually used with 2 ohm source impedance as mains would be). You do occasionally see surge ratings on relays, which are usually in this range when seen, so, you might just shop around for one with adequate ratings and call it good.
The biggest risk I suppose, is poorly-settled/wiped contacts with high initial resistance, and then the pulse comes in and welds them together. You might want two in series, or a higher reliability sort of contactor, or something that can read and confirm that the contacts have opened, or to monitor that the circuit has been deenergized.
Note that most mains contactors, motor starters, etc. only push the contacts together; independent springs open them back up. One or more circuits can get stuck in place, while the armature returns to resting position. Or the armature may get stuck in place, but not necessarily all contacts (including the side / sense / NC control contact) will be held in that case. (I haven't seen this many times myself; I did once weld a contactor and the armature was stuck, but I didn't happen to check the state of all the contacts. Designs may vary, anyway; most are of the contact-pair with armature pushing down a bridging part design, but there are probably others.)
Continuous plus switching rating is most certainly not required, but you can go the maximum-confidence route that way if needed.
Heh also fancy exotica, like, a mercury displacement relay comes to mind. No contact to weld if the contact is already molten. Usually used for soft and reliable switching (internal arcing can only produce more mercury vapor, at least until the housing melts or explodes), and obviously there's no contact wear to speak of. Probably not worthwhile here, but may be of interest.
Tim