Figure 9.5 Toxic gas indicator




expressed in parts per million (ppm). Some tubes, however, require the colour change to be matched against a control provided with the instruction manual. As tubes may have a specific shelf life, they are date-stamped and are accompanied by an instruction leaflet which lists any different gases which may interfere with the accuracy of the indication.

When using this type of instrument, it is important to aspirate the bulb correctly if reliable results are to be obtained. Normally, the bellows are compressed and the unbroken tube inserted. By this means the instrument is checked for leaks prior to breaking the tube. If found to be faulty, it should be replaced.

This type of instrument can also be used to good effect during gassing-up operations when changing from one cargo to another. By using tubes suitable to detect trace amounts of the previous cargo, a careful estimation can be made regarding a suitable cut-off point for the operation.

9.8 ENTRY INTO ENCLOSED SPACES

9.8.1 Precautions for tank entry

Because of the danger of hazardous atmospheres, an enclosed space should only be entered when it is essential to do so. At such times a permit to work should be issued and this should be specific as to date, time and space concerned and list the precautions to be taken. Alternatively, for ship tank entry purposes, the Maritime Safety Card should be completed. An example of this card, from IMO's International Maritime Dangerous Goods Code (Supplement) (see Reference 1.7), is reproduced in Figure 9.6.

The Maritime Safety Card gives an appropriate procedure for entering enclosed spaces on ships.

Particular hazards atmospheres can include:—

• Amounts of hydrocarbon gas

• Trace amounts of toxic gas

• The intrusion of inert gas, and

• Oxygen deficiency (often caused by the rusting process in unventilated tanks)

The table below lists those spaces on a gas carrier which are either enclosed or which may be considered gas-dangerous for entry.

Table 9.4 Enclosed spaces on gas carriers

enclosed spaces ON gas carriers INCLUDE:—

 

Enclosed Spaces in Cargo Area Enclosed Spaces Elsewhere Encloses Spaces Entered Routinely
cargo tanks   void spaces   compressor rooms  
hold spaces   bunker tanks      
interbarrier spaces   cofferdams      
duct keels   ballast tanks      
spaces containing cargo pipes   spaces adjacent to cargo spaces having unsafe atmospheres      

Note:— Even if a space is already considered gas-free and fit for entry, where it is immediately adjacent to a tank having a dangerous and pressurised atmosphere, the space should always be entered with caution and only after suitable checks have been made.

 

 


MARITIME SAFETY CARD

Entering cargo spaces, tanks, pump-rooms, fuel tanks, cofferdams, duct keels, ballast tanks and similar enclosed compartments

GENERAL PRECAUTIONS

Do not enter an enclosed space unless authorised by the master or a responsible officer and only after all the appro­priate safety checks listed opposite have been carried out.

The atmosphere in any enclosed space may be incapable of supporting human life. It may be lacking in oxygen content or contain flammable or toxic gases. This also applies to tanks which have been inerted.

The master or a responsible officer should ensure that it is safe to enter an enclosed space by:

.1 ensuring that the space has been thoroughly ventilated by natural or mechanical means;

.2 testing the atmosphere of the space at different levels for oxygen deficiency and harmful vapour where suitable instruments are available; and

.3 requiring breathing apparatus to be worn by all persons entering the space where there is any doubt as to the adequacy of ventilation or testing before entry.

WARNING

Where it is known that the atmosphere in an enclosed space is unsafe it should only be entered when it is essential or in an emergency. All the safety checks should be carried out before entry and breathing apparatus must be worn.


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