The credit card processing companies may have added much needed fault-tolerance and redundancy to their systems, but from a consumer’s perspective, there are many more factors that need to be functioning in order to keep a credit card useful.

First of all, the point of sale (POS) equipment, i.e. registers, need to be functional for credit card purchases to be successful. This may sound obvious, but large emergencies are notorious for stores losing power, getting water in the registers, causing looters to break the equipment, cables or equipment being torn or damaged from falling objects, etc. Frequently, the registers don’t survive long in an emergency.

Also, POS equipment uses one form or another of electronic communications to relay your purchase to and obtain approval from the credit card processor network. Larger retailers may use the internet or communicate directly to a central office via ISDN, cable, DSL, fiber optic, or even satellite, while smaller retailers will use the good ol’ dial-up modem for this purpose. (You can even hear the AOL-era squealing coming from the registers at some places.) The phone lines could be jammed, the cable company could lose power, a utility pole could fall, a central office or remote terminal could flood or fry, etc. A localized emergency could very easily take out the communications network in an area far greater than the actual emergency area. You may get lucky and be in a store that still uses those press rollers to get an imprint of your card, but you’d still have to be lucky enough for their paper to be dry.

There are just too many points where a credit card purchase can fail. All the fault-tolerance in the world only ensures that the credit card processing companies still exist after the emergency, not that they can help those being affected by it.