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ENTRY INTO ENCLOSED SPACES
The contents of this section are extracts from ISGOTT.
An Enclosed Space is defined as one with restricted access that is not subject to continuous ventilation, and in which the atmosphere may be hazardous due to the presence of hydrocarbon, toxic or inert gas, or oxygen deficiency.
Such spaces include, but are not limited to, cargo, slop, ballast, water, fuel, lub oil, waste oil, and sewage tanks, cofferdams, duct keels, void spaces, trunkings, pipelines, inert gas scrubbers and deck seals, and any other item of machinery or equipment that is not routinely ventilated and entered, such as boilers and main engine crankcases.
A pumproom is not, therefore, an enclosed space as such, although entry precautions, as defined in this section, are required.
An Enclosed Space Entry Permit is a document issued by a responsible person permitting entry to a space or compartment during a specific time interval. A permit should be completed only for a single space or compartment, and should include the checks and information contained in the sample form in Appendix 1 of ISGOTT, a copy of which is included in this section.
ATMOSPHERE TESTS PRIOR TO ENTRY
Any decision to enter an enclosed space should only be taken after the atmosphere within the space has been comprehensively tested from outside the space with test equipment that has recently been calibrated and checked for correct operation. To be considered safe for entry a reading of not more than 1% LFL must be obtained.
Care should be taken to obtain a representative cross-section of the compartment by sampling at several depths and through as many deck openings as practicable. When tests are being carried out from deck level, ventilation should be stopped and a period of about 10 minutes allowed to lapse before readings are taken.
Even when tests have shown a tank or compartment to be safe for entry, pockets of gas should always be suspected, and regeneration of hydrocarbon gas should always be considered possible, even after loose scale has been removed. Therefore the use of personal detectors capable of continuously monitoring the presence of hydrocarbon vapour the oxygen content of the atmosphere, and, if appropriate, toxic vapour, is strongly recommended.
While personnel remain in a tank or compartment, ventilation should be continuous and frequent atmosphere tests should be taken.
To be considered safe for entry a reading of not more than 1% of the LFL (also referred to as LEL), of hydrocarbon vapour must be obtained. In some cases the gases may impair the sense of smell, and therefore the absence of smell should never be taken to indicate the absence of gas.
The main effect of petroleum gas is to produce narcosis, followed, at high concentrations, by paralysis, insensibility and death.
A TLV (Threshold Limit Value - the time weighted average concentration of a substance to which a person may be repeatedly exposed for 8 hours a day or 40 hours a week, day after day, without adverse effect), of 300 ppm, corresponding to 2% of the LFL, or about 0.02% by volume of gas, has been established for gasoline vapours, but this figure should not be used if concentrations of benzene, hydrogen sulphide or other toxic vapours are suspected.
Combustible gas indicators which measure total gas content by volume cannot be expected to measure concentrations of this order accurately.
Before entry is allowed into any enclosed space which is not in daily use, the atmosphere should be tested to ensure that the normal oxygen level in air of 21% by volume is present. Oxygen deficiency should always be suspected in all enclosed spaces, particularly if they have contained water, have been subjected to damp or humid conditions, or have contained inert gas.
While individuals vary in susceptibility, all will suffer impairment if the oxygen level falls to 16% by volume. Exposure to an atmosphere containing less than 10% oxygen inevitably causes unconsciousness, that containing less than 5% causes immediate unconsciousness with no warning other than a gasp of air.
The main hazard associated with inert gas is itís low oxygen content. However, inert gas produced by combustion contains trace amounts of toxic gases which may increase the hazard to personnel exposed to it.
The aromatic hydrocarbons include benzene, toluene and xylene, and these substances are found in many typical petroleum cargoes such as gasolines, reformates, naphthas, special boiling point solvents, turpentine substitute, white spirits and crude oil. The TLV of an aromatic hydrocarbon is generally less than that of other hydrocarbons.
Checks for benzene vapour should be made prior to entering any compartment in which a cargo that may have contained benzene has been carried. Appropriate detecting equipment, such as detector tubes, should be used, and entry not permitted without personal protective equipment if recommended PELís (Permissible Exposure Limits - usually expressed in either TWA: Time Weighted Average, the airborne concentrations of a toxic substance averaged over an 8 hour period, or STEL: Short Term Exposure Limit, the airborne concentration of a toxic substance averaged over any 15 minute period, both usually expressed in ppm) are likely to be exceeded.
Repeated exposure to high levels of benzene vapour may have chronic effects. It primarily presents an inhalation hazard, and has poor warning qualities as itís odour threshold is well above the PEL. It can be absorbed through the skin, and exposure to vapour concentrations in excess of 1,000 ppm can lead to unconsciousness and death.
The atmosphere of a tank which has contained sour crude or sour products should be checked and entry prohibited in the event of hydrogen sulphide being detected. However, if the tank has been thoroughly washed the hydrogen sulphide should have been eliminated.
Hydrogen sulphide can also be encountered in other cargoes such as naphtha, fuel oil, bitumens and gas oils.
The PEL of hydrogen sulphide expressed as a TWA is 10 ppm.
It is important to distinguish between concentrations of hydrogen sulphide in the atmosphere expressed in ppm by volume and concentrations in liquid expressed in ppm by weight. A crude oil containing 70 ppm by weight has been shown to produce a concentration in the gas stream leaving the ullage port above a cargo tank of 7,000 ppm by volume. It is, therefore, not possible to predict the likely vapour concentration from known liquid concentrations.
Tetraethyl Lead, Tetramethyl Lead:
The amounts of these substances normally added to gasolines are insufficient to render the gases from these products significantly more toxic than those from unleaded gasolines.
CONDITIONS FOR ENTRY INTO ENCLOSED SPACES
No one should enter any cargo tank, cofferdam, double bottom or other enclosed space unless an entry permit issued by a responsible officer, who has ascertained immediately before entry that the atmosphere within the space is in all respects safe for entry, has been completed.
Before issuing an entry permit, the responsible officer should ensure that:
- the appropriate atmosphere checks have been carried out, namely the oxygen content is 21% by volume, hydrocarbon vapour concentration is less than 1% LFL, and no toxic or other contaminants are present;
- effective ventilation will be maintained continuously whilst personnel are in the space;
- lifelines and harnesses are ready for immediate use at the entrance,
- breathing apparatus and resuscitation equipment are ready at the entrance,
- where possible, a separate means of access is available for use in an emergency;
- a responsible member of the crew is in constant attendance outside the space, and in direct contact with a responsible officer;
- regular atmosphere tests are carried out all the time personnel are within the space, and a full range of tests undertaken prior to re-entry after any break;
- the use or personal detectors and the carriage of emergency escape breathing apparatus is recommended;
- terminal approval may be required if the vessel is within port limits.
Suitable notices should be prominently displayed to inform personnel of the precautions to be taken when entering tanks or other enclosed spaces, and of any restrictions placed upon the work permitted therein.
The entry permit should be rendered invalid if ventilation of the space stops, or if any of the conditions in the check list change.
Note: Failure to use enclosed space entry permits when required should be assessed as high risk.
Entry into any space that has not been proved to be safe for entry should only be considered in an emergency situation when no practical alternative exists. In this highly hazardous situation the personnel involved must be well trained in the use of breathing apparatus and be aware of the dangers of removing their face masks while in the hostile atmosphere.
Cargo pumprooms, by virtue of their Circulars, design and operation, which require the space to be routinely entered by personnel, constitute a particular hazard and therefore necessitate special precautions.
Because of the potential for the presence of hydrocarbon gas, Solas requires the use of mechanical ventilation to maintain the atmosphere in a safe condition. The pumproom should be continuously ventilated during all cargo operations.
Pumproom fans should be operated in the extraction mode. Some vessels, however, have a ventilation system which has been designed with one fan venting and the other extracting. This is acceptable provided extraction takes place from both sides of the pumproom bilges, and the ventilating fan delivers to the upper part of the pumproom.
Note: An observation should be made if this is not the case, and this should be made high priority if the ventilation system is not being operated correctly, or if there is inadequate exhausting of the bilge area.
Occasionally the venting system is fitted with high level suctions at or above the bottom gratings, the flaps of which are operable from the pumproom top.
The purpose of these suctions is to allow the fans to be operated when the bilges are flooded, and the flaps should, under normal operation, be closed.
Before anyone enters a pumproom it should be thoroughly ventilated, and the atmosphere checked for oxygen content and hydrocarbon and, where necessary, toxic gases.
It is strongly recommended that operators develop procedures to control pumproom entry, regardless of whether or not a fixed gas detection system is in use. Clear procedures should be established with regard to undertaking pre-entry checks, gas testing, and subsequent regular atmosphere monitoring. In addition, procedures should include the use of personal gas monitors for those entering the space.
Note: An Ďotherí observation should be made if personal monitors are not being used.
It is not necessary to complete an enclosed space entry permit before each entry into a pumproom.
Notices should be displayed at the pumproom entrance prohibiting entry without permission, and detailing the procedure to be followed before entry.
The frequency of pumproom entry for routine inspection during cargo operations should be reviewed with a view to minimising personnel exposure.
A communication system should provide links between the pumproom, navigation bridge, engine room and cargo control room. Audible and visual repeaters for essential alarm systems, such as the general alarm, should be provided within the pumproom.
It is an unsafe practice to drain pumproom lines into the bilges, and it is recommended that consideration be given to the provision of a comprehensive stripping arrangement to enable all lines and pumps to be stripped to a cargo tank, with the aim of preventing a volatile product being drained to the bilge.
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