| Entering Enclosed or Confined Spaces |
| Page 1 of 2 |
| General |
 The
atmosphere of any enclosed or confined space may put at
risk the health or life of any person entering it. It may
be deficient in oxygen and/or contain flammable or toxic
fumes, gases or vapours. Such an unsafe atmosphere may be
present or arise subsequently in any enclosed or confined
space including cargo holds, double bottoms, cargo tanks,
pump rooms, compressor rooms, fuel tanks, ballast tanks,
cofferdams, void spaces, duct keels, inter-barrier
spaces, sewage tanks, cable trunks, pipe trunks, pressure
vessels, battery lockers, chain lockers, inert gas plant
scrubber and blower spaces and the storage rooms for CO2, halons and other media used for fire
extinguishing or inerting. Should there
be any unexpected reduction in or loss of the means of
ventilation of those spaces that are usually continuously
or adequately ventilated then such spaces should also be
dealt with as dangerous spaces. When it is
suspected that there could be a deficiency of oxygen in
any space, or that toxic gases, vapours or fumes could be
present, then such a space should be considered to be a
dangerous space. |
| Precautions on Entering Dangerous Spaces |
| The
following precautions should be taken as appropriate
before a potentially dangerous space is entered so as to
make the space safe for entry without breathing apparatus
and to ensure it remains safe whilst persons are within
the space. 1./ A competent person should make an assessment of the space and a responsible officer to take charge of the operation should be appointed 2./ The potential hazards should be identified 3./ The space should be prepared and secured for entry 4./ The atmosphere of the space should be tested 5./ A 'permit-to-work' system should be used 6./ Procedures before and during the entry should be instituted Where the
procedures listed at 1 to 4 in the previous paragraph
have been followed and it has been established that the
atmosphere in the space is or could be unsafe then the
additional requirements including the use of breathing
apparatus should be followed. No one
should enter any dangerous space to attempt a rescue
without taking suitable precautions for his own safety
since not doing so would put his own life at risk and
almost certainly prevent the person he intended to rescue
being brought out alive. |
| Duties and Responsibilities of a Competent Person and of a Responsible Officer |
| A
competent person is a person capable of making an
informed assessment of the likelihood of a dangerous
atmosphere being present or arising subsequently in the
space. This person should have sufficient theoretical
knowledge and practical experience of the hazards that
might be met in order to be able to assess whether
precautions are necessary. This assessment should include
consideration of any potential hazards associated with
the particular space to be entered. It should also take
into consideration dangers from neighbouring or connected
spaces as well as the work that has to be done within the
space. A
responsible officer is a person appointed to take charge
of every operation where entry into a potentially
dangerous space is necessary. This officer may be the
same as the competent person (see above) or another
officer. Both the competent person and/or the responsible
officer may be a shore-side person. It is for
the responsible officer to decide on the basis of the
assessment the procedures to be followed for entry into a
potentially dangerous space. These will depend on whether
the assessment shows:- (a) there is no conceivable risk to the life or health of a person entering the space then or at any future time; (b) there is no immediate risk to health and life but a risk could arise during the course of work in the space; (c) the risk to life or health is immediate. Where the
assessment shows that there is no conceivable risk to
health or life and that conditions in the space will not
change entry may be made without restriction. Similarly
an assessment could be made that there is a risk which is
then entirely eliminated with no foreseeable chance
whatsoever of it recurring. Entry thereafter could also
be made without restriction. Where the
assessment shows that there is no immediate risk to
health and life but that a risk could arise during the
course of work in the space the precautions described in
paragraphs below should be taken as appropriate. For inland
water vessels such as harbour craft either or both the
competent person and the responsible officer may only be
available from shore-based personnel. No entry into a
potentially dangerous space should be made in these
circumstances until such suitably qualified persons are
available . |
| Identifying
Potential Hazards Oxygen Deficiency |
| If an
empty tank or other confined space has been closed for a
time the oxygen content may have been reduced due to the
oxygen combining with steel in the process of rusting. Lack of
oxygen may occur in boilers or other pressure vessels
particularly where oxygen absorbing chemicals have been
used to prevent rusting . Depletion of
oxygen may occur in cargo spaces when oxygen absorbing
cargoes, for example, oil cake and other vegetable and
animal oil bearing products, certain types of wood
cargoes, steel products, iron and steel swarf etc., are
or have been carried. Oxygen
deficiency can also occur in cargo holds e.g. when
carrying ore concentrates even though the hatch covers
have been removed and the discharge of cargo has
commenced. After
discharge of volatile cargoes sufficient vapours may
remain in tanks to cause oxygen deficiency. Hydrogen may
occur in a cathodically-protected cargo tank used for
ballast but will tend to disperse quickly when tank
covers are opened. Pockets of hydrogen may, however,
still exist in the upper parts of the compartment, thus
displacing the oxygen (as well as creating a possible
explosion hazard). If carbon
dioxide, steam or other fire extinguishing chemical has
been discharged to extinguish or prevent
a fire, the oxygen content of the space would be
reduced. The use of
inert gas in the cargo tanks of tankers and gas carriers
or in the inter-barrier spaces of gas carriers results in
only minimal amounts of oxygen being present. The special
conditions of carriage for reactive substances may
require cargo tank ullage spaces, adjacent cargo tanks,
cofferdams, inter-barrier spaces and void spaces to
contain inert gas. |
| Toxicity of Oil Cargoes |
|
Hydrocarbon gases are flammable as well as toxic and may
be present in fuel or cargo tanks which have contained
crude oil or its products . Hydrocarbon
gases or vapours may also be present in pump rooms and
cofferdams, duct keels or other spaces adjacent to cargo
tanks due to the leakage of cargo. The
components in the vapour of some oil cargoes, such as
benzene and hydrogen sulphide are very toxic. |
| Toxicity of Other Substances |
| Cargoes
carried in chemical tankers or gas carriers may be toxic. There is the
possibility of risk of leakage from drums of chemicals or
other packages of dangerous goods where there has been
mishandling or incorrect stowage or damage due to heavy
weather. The trace
components in inert gas such as carbon monoxide, sulphur
dioxide, nitric oxide and nitrogen dioxide are very
toxic. The
interaction of vegetables or animal oils or sewage with
sea water may lead to the release of hydrogen sulphide
which is very toxic. Hydrogen
sulphide or other toxic gases may be generated where the
residue of grain or similar cargoes permeates into or
chokes bilge pumping systems. The chemical
cleaning, painting or the repair of tank coatings may
involve the release of solvent vapours. |
| Flammability |
|
Flammable vapours may still be present in cargo or other
tanks that have contained oil products or chemical or gas
cargoes. Cofferdams
and other spaces that are adjacent to cargo and other
tanks may contain flammable vapours should there have
been leakage into the space. |
| Other Hazards |
| Although
the inhalation of contaminated air is the most likely
route through which harmful substances enter the body,
some chemicals can be absorbed through the skin. Some of the
cargoes carried in chemical tankers and gas carriers are
irritant or corrosive if permitted to come into contact
with the skin. The
disturbance of rust, scale, or sludge residues of cargoes
of animal, vegetable or mineral origin, or of water that
could be covering such substances may lead to the release
of toxic or flammable gases. |
| Preparing and Securing the Space for Entry |
| When
opening the entrance to a dangerous space care should be
taken to avoid the effects of a possible release of
pressure or vapour from the space. The space
should be isolated and secured against the ingress of
dangerous substances by blanking off pipe lines or other
openings or by closing valves. Valves should then be tied
or some other means used to indicate that they are not to
be opened. If
necessary, the space should be cleaned or washed out to
remove as far as practicable any sludge or other deposit
liable to give off dangerous fumes. The space
should be thoroughly ventilated by either natural or
mechanical means to ensure that all harmful gases are
removed and no pockets of oxygen deficient atmosphere
remain. Compressed
oxygen should not be used to ventilate any space. The officers
on watch, or persons in charge, on the bridge, on the
deck, in the engine room, or the cargo control room
should be informed, as necessary, of any space that is to
be entered so that they do not, for example, stop fans,
start equipment or open valves by remote control, close
escape doors or pump cargo or ballast into the space and
appropriate warning notices should be placed on the
relevant controls or equipment. Where necessary pumping
operations or cargo movements should be suspended when
entry is being made into a dangerous space. |
| Testing the Atmosphere of the Space |
| Testing
of a space should be carried out only by persons trained
in the use of the equipment. Testing
should be carried out before entry and at regular
intervals thereafter. If possible,
the testing of the atmosphere before entry should be made
by remote means. If this is not possible, the person
selected to enter the space to test the atmosphere should
only do so in accordance with the additional precautions
specified in Section "Additional
Requirements for Entry into a Space where the Atmosphere
is Suspect or Known to be Unsafe" , which
include the wearing of breathing
apparatus. Where
appropriate, the testing of the space should be carried
out at different levels. Personal
monitoring equipment designed purely to provide a warning
against oxygen deficiency and hydrocarbon concentrations
when there is a change in conditions should not be used
as a means of determining whether a dangerous space is
safe to enter. |
| Testing for Oxygen Deficiency |
| A steady
reading of at least 20% oxygen by volume on an oxygen
content meter should be obtained before entry is
permitted. A
combustible gas indicator cannot be used to detect oxygen
deficiency. |
| Testing for Flammable Gases or Vapours |
| The
combustible gas indicator (sometimes called an
explosimeter) detects the amount of flammable gas or
vapour in the air. An instrument capable of providing an
accurate reading at low concentrations should be used to
judge whether the atmosphere is safe for entry. Combustible
gas detectors are calibrated on a standard gas and when
testing for other gases and vapours reference should be
made to the calibration curves supplied with the
instrument. Particular care is required should
accumulations of hydrogen be suspected. In deciding
whether the atmosphere is safe to work in without being
overcome, a 'nil' reading on a suitably sensitive
combustible gas indicator is desirable but, where the
readings have been steady for some time, up to 1% of
lower flammable limit may be accepted, e.g. for
hydrocarbons in conjunction with an oxygen reading of at
least 20% by volume. Direct
measurement of trace components of inert gas is not
required when the gas freeing of the atmosphere of a
cargo tank reduces the hydrocarbon concentration from
about 2% by volume to 1% of lower flammable limit or less
in conjunction with a steady oxygen reading of at least
20% by volume, because this is sufficient to dilute the
components to a safe concentration. If, before the
commencement of gas freeing, the hydrocarbon
concentration of a tank containing inert gas is below 2%
by volume due to excessive purging by inert gas, then
additional gas freeing is necessary to remove toxic
products introduced with the inert gas. It is difficult
to measure the quantities of these toxic products at the
safe level without specialized equipment and trained
personnel. If this equipment is not available for use,
the period of gas freeing should be considerably
extended. |
Testing for Toxic Gases Use of a permit-to-work System Procedures and Arrangements before Entry Procedures and Arrangements During Entry Additional Requirements for Entry into a Space where the Atmosphere is Suspect or known to be Unsafe Drills and Rescue Breathing Apparatus and Resuscitation Equipment Maintenance of Equipment Training of Equipment Training, Instruction and Information Statutory Regulations |
