As someone who was an airfield firefighter prior to becoming a helicopter pilot:
No way in hell would I have tried to physically block the aircraft with an appliance (armoured or not!). Massive risk to the appliance and it's occupants and huge risk to the occupants of the helicopter (who could still be alive and then be killed by the impact). And that's before we even consider the legal / liability consequences.
I would have thought very hard about foaming it - it would have been tempting indeed, but as others have said, i think the chances of it successfully suffocating the engine would be small in comparison to the risk of suffocating the occupants. I'd also have been very wary about the presence of the foam blanket making the surface slipperier and causing the aircraft to spin and slide more violently and unpredictably.
I find the criticism of the fire-crews quite harsh and unfair - this was a one-in-a-billion event that they were faced with.
OH