Any space which has limited openings for entry and exit, inadequate ventilation and not designed for continuous worker occupancy is an Enclosed Space.
A Shipping container meets the definition of, and is, an enclosed space! A container may have oxygen depleted or enriched atmosphere, further, due to the presence of dangerous goods, may have, corrosive, toxic or flammable atmosphere.
There are many cases involving workers dying in sewage duct or enclosed spaces on board ships. Co-workers go in to rescue those fallen without realizing the danger or low oxygen or presence of toxic or flammable atmosphere and fall victim themselves. More than 50% of death in enclosed spaces occur while attempting to rescue others.
Master’s Guide published by Standard P&I Club identifies the common factors as
- failure to recognise an enclosed space
- failure to recognise the hazards involved in enclosed space entry
- tendency to trust to physical senses
- tendency to underestimate the danger
- complacent attitude
- attempt to save a co-worker
Oxygen Depleted Atmosphere: Earth’s atmosphere contains 20.8% of oxygen, if the percentage goes up or down then we are in a dangerous situation. First let us look at reduction of oxygen.
There are many cargoes which can cause depletion of oxygen, corroding scrap metals can deplete oxygen in a closed container or cargo hold of a ship. Oil Seeds, Copra, Fishmeal, Dry Ice, Charcoal etc. may cause serious depletion in oxygen level.
Any atmosphere which has less than 19.5% oxygen is oxygen depleted atmosphere however one shall not enter any place where oxygen level is less than 20.8%!!
Oxygen Enriched atmosphere : Oxygen enrichment can be caused by various sources like, leaking oxygen cylinders, chemical reactions, inadvertent or accidental activation of oxygen generators carried as cargo etc. If the atmosphere is enriched with oxygen combustible materials can catch fire more easily and will burn more vigorously.
Oxygen enriched, depleted or containers having toxic or flammable atmosphere are too dangerous to enter and have resulted in fatalities in the past.
A fumigated container even after loaded as ventilated may have toxic fumigant gas present in it. Either natural or forced ventilation must be employed prior entering for devanning.
IMDG Code 36th amendment section 184.108.40.206 warns the possibility of unsafe condition, concentration of toxic or flammable vapours, or an oxygen-enriched or oxygen-depleted atmosphere and advise to take necessary caution prior opening the doors of a container.
Prior devanning an import container the risk factor can be placed into three levels.
Level 1 – High Risk – The container contains dangerous gases (example fumigated)
Level 2 – Medium Risk – The container may contain dangerous gases, enriched or depleted level of oxygen (example ventilated fumigated containers, volatile liquids, oxygen depleting goods or gas as cargo)
Level 3 – Low Risk – Probability of oxygen enriched, depleted or hazardous atmosphere is remote.
Ventilation methods: Ventilation prior entering can be either natural ventilation or mechanical. Various factors must be borne in mind while carrying out ventilation and entering the unit. Some gases may take longer to dissipate than others. 1,2-dichloroethane and methyl bromide are less volatile and may adhere to the goods. The time required for natural ventilation must be ascertained depending on the nature of gas, ambient temperature and wind speed. A near zero wind speed may have little or no ventilation effect and the dangerous gases may linger at the door end. Lower the ambient temperature slower evaporation of fumigant gases. Similarly goods which absorb gases such as cotton bales, mattresses, cloths etc. can take longer time for complete ventilation.
A 40 ft container will take twice as much time for ventilating a 20 ft container with similar levels of gas.
For carbon dioxide, carbon monoxide or oxygen ventilation time needed is lesser due to faster degasing properties of these gases. Minimum 2 hours ventilation may be sufficient, for other gases best recommended practice is 24 hours ventilation.
Forced ventilation can be achieved with either using powerful fans or degassing door. Forced ventilation has an advantage of minimizing time required for ventilation.
Never enter the unit while ventilation is in progress. The unit must be clearly marked with warning signs or approach restricted. For highly toxic gases such as sulfuryl fluoride, phosphine and methyl bromide a minimum safe distance of 20 meters must be maintained. Prior entering, after ventilation, presence of toxic, flammable, corrosive gas and oxygen level must be measured. When in doubt contact a specialist or company who has expertise in degassing containers.
Common fumigants: Acrylonitrile, Carbon disulphide, Carbon tetrachloride, Chloropicrin, Dichlorvos (DDVP),Ethylene dibromide, Ethylene dichloride, Ethylene oxide, Ethyl formate, Hydrogen cyanide, Methyl bromide, Methyl formate, Paradichlorobenzene, Phosphine, Sulphuryl fluoride, Trichloroethylene.
An ISO tank is an enclosed space, it may have presence of dangerous gases or oxygen depleted condition. Those who are entering an ISO tank for any purpose must be trained and aware of the procedures for safe entry into enclosed spaces.
On board ships enclosed spaces are cargo spaces, double bottoms, fuel tanks, ballast tanks, cargo pump-rooms, cargo compressor rooms, cofferdams, chain lockers, void spaces, duct keels, inter-barrier spaces, boilers, engine crankcases, engine scavenge air receivers, sewage tanks, and adjacent connected spaces etc. From 1st January 2015 amendment of SOLAS regulation III/19, on emergency training and drills, mandate enclosed-space entry and rescue drills, which will require crew members with enclosed-space entry or rescue responsibilities to participate in an enclosed-space entry and rescue drill at least once every two months.