Introduction
Where the dangers exist
When does the air become unsafe?
Safety precautions
Wet fish in storage consume oxygen and produce poisonous gases as they spoil. In an enclosed space the atmosphere can eventually become so seriously polluted and deficient in oxygen that it will cause illness or even death to someone breathing it. The risk of an accident is greatest when fish are stored in bulk without ice, as is the practice on vessels engaged in industrial fishing, and in fish meal plants on shore where catches are also stored.
This note describes the hazards and how they occur, gives an indication of the level of pollution at which the atmosphere becomes unsafe, and outlines the safety measures that must be observed by crew and by shore workers when handling industrial fish.
It has been known for many years that a trawler fishroom full of fish in ice, closed for several days during the homeward passage of the vessel, is dangerous to enter immediately after the hatches are opened in port. At one time shore workers preparing to discharge the catch used to make a simple check by lowering a lighted candle through the hatchway; if the flame went out, there was insufficient oxygen present. Nowadays the hatch covers are removed at least 1 hour before unloading begins, and blowers are available at some ports to ventilate the fishroom if required. Improved stowage practice and a reduction in the number and duration of long voyages in recent years have helped to prevent any serious risk during discharge of fish for human consumption.
The increase in industrial fishing, that is the capture of fish for reduction to meal and oil, has, however, resulted in a number of serious incidents both abroad and in the UK, mainly during discharge of the catch. Workers in fishrooms and in raw material stores at fish meal plants have suffered bouts of dizziness, loss of consciousness, suffocation and respiratory poisoning; in some instances workers have died without recovering consciousness. Lives have been lost in multiple accidents when fellow workers attempting rescue have themselves been overcome. Some who have recovered initially have contracted eye disease and other persistent effects.
The principal factors that contribute towards the rapid formation of a dangerous atmosphere are a relatively high temperature and lack of ventilation; fish without ice or other means of cooling spoil rapidly, using up oxygen from the air as they do so and replacing it with carbon dioxide and poisonous gases that are harmful even in small amounts. If the airspace is unventilated, as in a closed fishroom for example, the atmosphere can become dangerous within hours rather than days. There is sometimes still a danger after a fishroom has been emptied; polluted air, heavier than clean air, can persist in the bottom of a poorly ventilated fishroom, making it dangerous for cleaners to enter. Water used during unloading, for example in a wet pump discharge system, becomes polluted and is sometimes returned to the empty fishroom from shore holding tanks for subsequent disposal at sea; bacterial action in the polluted water can affect the surrounding fishroom air in the same way as spoiling fish and so produce a dangerous atmosphere.
Other parts of a ship besides the fishroom can occasionally become dangerous when a catch of industrial fish is being carried; poisonous air can escape from the fishroom into the accommodation, thus putting at risk members of the crew who are sleeping on board while the vessel is awaiting discharge for example. In some instances victims have succumbed and not been found for several hours.
Poisonous gases are not necessarily harmful at all levels; people can tolerate low concentrations for a long time, and a measure known as the threshold limit value has been devised to indicate the concentration of an airborne poison that can be tolerated for 8 hours a day without harmful effect by those exposed to it. The threshold limit value can be used as a guide, but some individuals, perhaps because of age or poor health, or the conditions to which they are exposed, may suffer discomfort or ill health at a level below the threshold value.
Analyses of samples of the air surrounding industrial fish stored for a few days in summer show the presence of carbon dioxide, hydrogen sulphide and ammonia in concentrations well above their threshold limit values, and a corresponding reduction in the level of oxygen present. The table gives the threshold limit value for these gases, and the level at which they cause acute danger to life.
|
Gas
|
Threshold limit value |
Acute danger to life |
|
% volume |
% volume |
|
|
carbon dioxide |
0·5 |
20 |
|
|
mg/m3 |
mg/m3 |
|
hydrogen sulphide |
15 |
990 |
|
ammonia |
18 |
3500 |
Stowage at sea of industrial fish
Fish stowed in bulk should be secured by pound boards to prevent movement; fish damaged by movement spoil and produce dangerous gases more quickly.
One man should be on watch at the hatchway whenever crew are working in the fishroom, so that help can be summoned immediately if there are danger signs.
Crew should be taught first aid, including mouth to mouth resuscitation.
A safety line should be kept on deck near the hatchway; when anyone enters the fishroom to rescue an unconscious man, there should be other crew members at the hatch, and the safety line should be used to prevent further casualties.
In port
Crew should not sleep aboard while the catch is still in the vessel; shore accommodation should be used until the fishroom has been emptied and ventilated.
Fishroom hatches should be removed several hours before unloading starts, and ventilators should be used before and during unloading to prevent the atmosphere above the cargo from becoming unsafe; discharge of some of the catch may cause sudden release of poisonous gases.
One man should be on watch at the hatchway whenever men are working in the fishroom.
Whenever a worker feels discomfort or becomes unwell he must be removed from the fishroom at once, and unloading must stop until the fishroom has been well ventilated.
A safety line should be kept on deck near the hatchway to avoid the risk of a multiple accident during rescue work.
Workers engaged in unloading should be taught first aid.
Anyone who becomes ill should seek medical advice at once.
Apparatus for analysing polluted air should be available at ports where industrial fish are handled, so that occasional checks can be made on fishroom conditions during discharge, and so that any accident can be investigated immediately.
In fish meal plants
The safety precautions recommended for fishroom work are also generally applicable to work in raw material stores at fish meal factories; spoiling fish held in bulk in pits, hoppers or unventilated rooms awaiting reduction can produce the same dangerous atmospheric conditions.
General
All those concerned with the catching and handling of industrial fish should be conversant with the risks involved and the precautions that are necessary. Fishermen and shore workers must understand that in cases of suffocation there is only a narrow margin between a feeling of faintness and death, and strict safety precautions must be taken at all times to avoid serious accidents.
The best way of reducing risk is to reduce the spoilage that pollutes the air; chilling of the catch with ice or chilled sea water would make industrial fish no more hazardous to handle than fish for human consumption, and at the same time would reduce the nuisance caused by smell and prevent high drip loss from the raw material. - If you have any queries, write, phono or call at either of the addresses given below:
|
The Director |
The Officer in Charge |
|
Torry Research Station |
Humber Laboratory |
|
PO Box 31 |
Wassand Street |
|
135 Abbey Road |
Hull |
|
Aberdeen |
HU3 4AR |
|
AB9 8DG |
|
|
Tel: 0224 877071 |
Tel: 0182 27879 |
