The learning objective of this chapter is to identify and become familiar with
precautionary measures for handling vapors in an enclosed or confined space
you this chapter deals with the safe
handling of the atmosphere inside the enclosed or confined space and the
isolation of the space from other compartments that is securing it against
hazardous liquids and vapors in adjacent or connected spaces
when opening the entrance to a potentially dangerous space precautions
should be taken in case vapor or gases are released from the space in some
circumstances such vapor may be released under pressure such conditions should
routinely be checked as part of preparation for entry into an enclosed
space if fitted and operational a remote
readout from a pressure sensor can be consulted if possible pressure should be
released in a controlled manner through an alternative route on deck such as a
pressure vacuum valve or ventilator if a lid or flange is used securing nuts or
dogs should be slackened back gradually and evenly allowing control release of
any pressure behind
the space should be isolated and secured against the ingress of dangerous
substances by blanking off pipelines or other openings and by closing all inter
connecting valves manual valve should be closed and locked where possible they
should be secured by a padlock and chain or similar means such as a specialized
locking device a heavy-duty cable tie or even a numbered seal to indicate that
they are not to be opened note that although these are all valid techniques
for securing valves the particular method required by the company safety
management system should be used warning notices should be placed on the relevant
remote control under machinery starting panels for preference these should be
proper isolation tags bearing recognized international symbols
so securing and labeling of equipment against inadvertent use and the posting
of corresponding warning notices is widely referred to as the lockout tagout
process testing an inspection of surrounding spaces should be done and
pipelines cleaned thoroughly prior to entry if hot work is to be performed
then the atmosphere in the adjacent space behind is just as dangerous and
must be carefully evaluated the duty officer should be notified of any
systems that have been isolated and secured are the personnel such as the
duty engineer should be advised as required
where necessary sludge your other deposits liable to give off fumes should
be cleaned out this of course may itself lead to the release of gases and
appropriate precautions should be taken personnel charged with removing such
deposits manually should use an externally generated air supply or a
self-contained breathing apparatus and the no circumstances should a filter
mask or canister type facemask be used in an atmosphere which is or may become
oxygen deficient the temptation to enter a space as quickly as possible for
operational reasons and irrespective of the continuing presence of any
outstanding hazards must be avoided and if necessary the space should be machine
clean further to remove remaining residues the space should be thoroughly
ventilated either by natural or mechanical means and then tested to
ensure that all harmful gases are removed and no pockets of oxygen
deficient atmosphere remain the time necessary to ensure complete removal of
any fumes will depend upon the size of the space the amount of framing which
may inhibit airflow within the space the density of any vapors the level of
initial contamination and the capacity and efficiency of the ventilation system
only once tested and certified as gas free by a competent person should a
space be considered safe and fit for unprotected entry
you
where necessary pumping operations or cargo movements should be suspended
when entry is being made into a dangerous space suspension of operations
may also be a regulatory requirement either under the company safety
management system or in compliance with local regulations if in Port this is not
only to increase the security and isolation of the space but to avoid
additional hazards arising from those other operations for example on a tanker
if cargo is being loaded at the time and vapor recovery is not being employed
then fumes are being expelled through the vent riders onto the cargo deck area
if mechanical fans are being used to ventilate an adjacent space prior to
entry then those fumes could be pulled inside the space and render it dangerous
to enter
if the vessel is at sea and entry is considered unavoidable she should reduce
speed and heave to in order to minimize any violent movement and should the
access be in an exposed area on deck to reduce the possibility of water entering
the space
we have already seen that Pump Rooms and in particular cargo Pump Rooms require
special entry precautions and procedures during cargo operations the ventilation
will be running continuously and any alarms will be switched on however if
the space has not been used for some time due for example to the vessel being
at sea on a loaded passage then this equipment will need to be switched on as
part of the preparations for entry in particular the fans should be run for
sufficient time to allow a thorough exchange of the air inside the space
the Hong Kong registered bulk carrier nigo Kim arrived off the port of Dampier
in the early hours of Saturday the 17th of November 2001 and anchored to await
birthing instructions she remained at anchor over the weekend during which
time the crew continued scheduled maintenance work including the
preparation of the interior of number one port topside ballast tank for
painting at about 1300 hours on Sunday the chief officer tested the atmosphere
inside the tank for oxygen content in accordance with standard enclosed space
entry procedures at about 1430 hours the eight-man deck crew started work
painting the steel work inside the tank one man was using an airless of spray
painting gun while the other crewman maintained the paint reservoir tended a
cargo light load through the after manhole and generally assisted the
painter as required ventilation of the tank was achieved by an open-ended
compressed air hose led from the fo'c'sle along the deck and down through
this after manhole and an electrically driven fan positioned at an angle over
the after manhole which also provided access for the paint hose light cable
and a lanyard the chief officer supervised the initial
stages of the task the paint used was a two-part epoxy mix thinned as needed
using the thinner product supplied by the paint manufacturer according to the
chief officer the volume of thinner used was between 30% and 50% of the total
mixture at about 1530 hours the chief officer went to the bridge to start his
anchor watch leaving the bosun and Dec fitter in
charge at the tank at about 16 40 hours a large explosion ripped through the
tank three men were blown down the length of the main deck killing them all
instantly four others were blown over the side one man who had been inside the
tank was still alive but severely burned he was assisted out of the tank through
the ruptured main deck plating and airlifted ashore but later died from his
injuries a search and rescue operation recovered
the body of one seaman but the others were never found
the investigation concluded that the air vapor ratio in particular stemming from
the paint thinner had developed into an explosive atmosphere and that it had
come into contact with a source of ignition it wasn't able to positively
identify that source other than to say it was within the compartment the
electrical lighting a VHF radio or a spark carried down from the electric fan
could all have been possibilities as could a falling tool or a cigarette
lighter it was noted that the prevailing good weather conditions would have
increased the temperature inside the tank to around 38 degrees Celsius which
was above the ignition temperature of the thinners although below the auto
ignition temperature analysis of the rate of delivery of fresh air revealed
that it was insufficient to prevent the atmosphere entering the flammable range
and that not being fitted with a trunking to carry the air to the lower
part of the space only the upper region of the tank was being ventilated