These days to become certified for use flight recorders must pass a collection of extremely arduous tests. These include:

Fire

This is two-fold, the flight recorder casings must protect the recording medium from 1100degC (the temperature at which aviation fuel burns) for thirty minutes (simulating the initial fuel fire after a crash). It must then be able to protect the recording medium from a temperature of 260degC for ten hours (this simulates a long baggage-fueled fire). Common heat-insulation materials used include polymers, wax and gelled which all offer good protection from high temperatures.

Water protection and Deep Sea Water Pressure Resistance

The casing must protect the recording medium for thirty days underwater at a pressure equivalent to being submerged at 20,000ft below the ocean surface.

Static Crush Test

The recorder must withstand a 5,000-pound pressure applied against all six axis points.

Penetration Resistance

The recorder must withstand a 500lb force being dropped on it from 10 feet up, the point of contact being a one-quarter inch diameter hardened steel spike.

Impact Test

In this test the recorder is fired from an air cannon into an aluminium wall. This simulates the required, 3400g deceleration in 6.5 milliseconds (which is equivalent to going from 350 mph to zero in 16 inches).

Fluid Immersion Test

To check that the recorder will not be eroded by any of the fluids that are most commonly carried by planes, the recorder must survive emersion for 48 hours in each of the following:
hydraulic fluid
lubricating oil
aviation fuel
fire extinguishing agents
and toilet flushing fluid

One other specification is the battery life of the ULB (see next section), the battery should have a shelf-life of 6 years and an operating life of 30 days.

The above are the internationally recognised standards.