Acceptance testing of emergency suits used at sea is in many countries based on the IMO requirements. For an uninsulated suit, it is required that the suit be capable of protecting the wearer from a core temperature drop of more than 2°C and that skin temperatures measured at the hand, foot and lumbar region do not drop below 10°C for a test period of 1 hour. The test should be performed in cold water of temperatures between 0 and 2°C. It is clear from the regulations that the tests are to be performed using human subjects.

Test results of suits are not only of interest to the approving authorities, but naturally also to the manufacturers. Rectal temperatures of the test subjects wearing the suit are commonly used as an "index" of the suit's thermal qualities. Unfortunately, rectal temperature does not always reflect the real properties of the suit when measured for a limited time.

Experiments have been carried out comparing the thermal qualities between completely dry suits and suits which had been pre-wetted inside with 0.6 1 of water prior to the start of the immersion period. Results indicated that the rectal temperature of the subject with the wetted suit stayed higher than that of the same subject in the dry suit. A Ventile fabric suit tested with or without a thinsulate inner lining showed the same confusing results: no difference in rectal temperatures was indicated. The explanation for the rather unexpected results for rectal temperature change is the fact that in the colder suits shivering will compensate for the increased heat loss.

A series of qualification tests of immersion suits indicated that the acceptance levels established by IMO were rather low with regards to thermal requirements and that any suit would meet these requirements. To test this, a "suit" was made by taping together plastic bags (0.5 mm thickness) and tested according to the IMO test protocol. The suit fulfilled the requirements for thermal protection.

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