At my airport, a lot of out checked luggage is screened underneath the airport, in an area where there is a lot of airline equipment...tugs, close to the tarmac, etc. I am not an expert on explosives, but if a grenade were to explode in this area, on the lowest level of the airport, near vehicles containing fuel, wouldn't that be a bad explosion? Wouldn't the structure of the airport be compromised, in a greater area than 90ft?
Perhaps that's a reason not to screen baggage near fuel, load-bearing supports, etc.; something that should be considered in advance, not when the first potential explosive is discovered.