Page 131 - International safety guide for oil tankers and terminals

SHIPBOARD SYSTEMS

7.1.7 Precautions to be Taken to Avoid Health Hazards
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7.1.7.1 Inert Gas on Deck

Certain wind conditions may bring vented gases back down onto the
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deck, even from specially designed vent outlets. Furthermore, if gases
are vented at low level from cargo hatches, ullage ports or other tank
apertures, the surrounding areas can contain levels of gases in harmful
concentrations and may also be oxygen deficient. In these conditions, all
non-essential work should cease and only essential personnel should
remain on deck, taking all appropriate precautions.

When the last cargo carried was a sour crude, tests should also be made
for hydrogen sulphide. If a level in excess of 5 ppm is detected, no
personnel should be allowed to work on deck unless they are wearing
suitable respiratory protection. (See Sections 2.3.6 and 11.1.9.)

7.1.7.2 Ullaging and Inspection of Tanks from Cargo Hatches
The low oxygen content of inert gas can cause rapid asphyxiation. Care
should therefore be taken to avoid standing in the path of vented gas (see
Section 11.8.3).

7.1.7.3 Entry into Cargo Tanks
ึ
Entry into cargo tanks should be permitted only after they have been gas
freed, as described in Sections 7.1.6.10 and 7.1.6.11. The safety
precautions set out in Chapter 10 should be observed and consideration
given to the carriage of a personal oxygen deficiency alarm. If the
hydrocarbon and oxygen levels specified in Section 7.1.6.12 cannot be
achieved, entry should be permitted only in exceptional circumstances
and when there is no practicable alternative. A thorough risk assessment
should be carried out and appropriate risk mitigation measures put in
place. As a minimum, personnel must wear breathing apparatus under
such circumstances (see Section 10.7 for further details).

7.1.7.4 Scrubber and Condensate Water

Inert gas scrubber effluent water is acidic. Condensate water, which tends
to collect in the distribution pipes, particularly in the deck main, is often
more acidic than the scrubber effluent and is highly corrosive.

Care should be taken to avoid unnecessary skin contact with either
effluent or condensate water. Particular care should also be taken to avoid
accidental contact with the eyes, so protective goggles should be worn
whenever there is a risk of such contact.

7.1.8 Cargo Tank Protection Against Over/Under-Pressure
Serious incidents have occurred on oil tankers due to cargo tanks being
subjected to extremes of over or under-pressure. Whilst SOLAS regulations
have been modified to require that tanks be fitted with full flow pressure relief
devices or individual tank pressure monitoring, it is still essential that venting
systems are thoroughly checked to ensure that they are correctly set for the
intended operation. Once operations have started, further checks should be
made for any abnormalities, such as unusual noises of vapour escaping under
pressure or pressure/vacuum valves lifting. (See Section 7.2.2 for detailed
information on the likely causes of tank over-pressurisation and
under-pressurisation and the precautions to be taken to avoid them.)

© ICS/OCIMF/IAPH 2006 97