While a CTD leak can result in a dangerous situation, it is not common. Pressure housings may flood under pressure due to dirty or damaged o-rings, or other failed seals, causing highly compressed air to be trapped inside. For example, a housing that floods at 5000 meters depth holds an internal pressure of more than 7000 psia. If this happens, a potentially life-threatening situation can occur when the instrument is brought to the surface. The CTD will not explode. If it does flood and develop pressure inside, the end cap can be shot out of the housing if a technician tries to open the unit without releasing the pressure first.
Possible causes of flooding include:
- O-rings were not properly prepared or greased after the housing was opened, or
- Instrument was dropped or hit hard, and a bulkhead connector or the sensor was cracked or damaged.
It is important to visually inspect the instrument for damage before each survey. A cracked bulkhead connector is usually easy to spot.
If the instrument is unresponsive to commands or shows other signs of flooding or damage, see the Recovery section in your instrument manual for details specific to your instrument. For most instruments, follow these precautions:
- Every time you open the instrument, loosen each end cap screw a few turns. If the end cap follows the screws out, there is pressure in the housing.
- If pressure in the housing is indicated:
A. Point the instrument in a safe direction away from people.
B. Loosen 1 of the bulkhead connectors very slowly, at least 1 turn, to release the pressure safely (bulkhead connectors are the black connectors on the end cap, where the cables attach to the instrument). This opens an O-ring seal under the connector. Look for signs of internal pressure (hissing or water leak). If internal pressure is detected, let it bleed off slowly past the connector o-ring. Then, you can safely remove the end cap.
In general, instruments do not flood. However, be aware of the potential for flooding so that if a problem arises you will be able to safely deal with it.