The Marine Firefighting Institute
Newsletter # 5
Hazards of Refrigeration In Ocean Shipping
By Tom Guldner
Since the beginning of time, man has attempted to store and transport food in such a way that it will not spoil. Drying and salting were the mainstays for centuries. Ice was used for some applications but it would not last for long voyages. As we extended our horizons and discovered new continents, we also discovered new and exotic foods. These foods, mostly tropical fruits, would not last on the long journey back to Europe. Therefore, for generations, people had to satisfy themselves with the drawings and paintings of these mysterious foods that were drawn by some naturalist who happened to encounter these fruits during an exploration voyage. Sometimes, the plants themselves could be kept alive on the voyage home. However, most of these were unable to survive when transplanted in the harsh climates of Northern Europe.
Mechanical refrigeration on ships can trace it roots to before 1915. The principal used is basically the same as that in service today. A series of evaporators and compressors remove the heat from an area. When a compressed liquid refrigerant is allowed to expand into a gas in the low pressure section of the system, it will absorb heat from the surrounding area. This warm gas is then re-compressed at another location (high pressure section) where the released heat can be expelled and moisture removed. Corby Refrigeration and Mechanical Services graphic on the right gives an example of a simple refrigeration process.
Early refrigeration used ammonia (NH3) throughout the system. This proved very hazardous whenever leaks developed in the refrigerated areas where workers might enter. Ammonia vapors are irritating and prolonged exposure and inhalation can cause serious injury and may be fatal. (Some of the "Old Buffalos" on the Fire Department will remember the ammonia leaks in the old refrigerators. When the housewife was defrosting the freezer she would speed up the process by chopping out blocks of ice with a knife or screwdriver. When she punctured the ammonia refrigerant line she and her neighbors would go running.) We would carry the refrigerator out to the street where the ammonia would vent itself "Exposure to 0.25 to 0.65 percent ammonia in the air for one-half hour is sufficient to cause death or serious injury."1
Due to this problem, a brine solution of chloride or sodium chloride was used as the coolant in the piping within the refrigerated area, and ammonia was only used as the refrigerant in the part of the system that did not enter occupied spaces. This type of system served the shipping industry until the start of the 1960s.
In the early '60s a new refrigerant was discovered. This new product was hailed as the "SAFE" refrigerant. The technical name of this class of refrigerants is "Chlorofluorocarbons". You might be able to recognize it more easily as "Freons". It was considered so much safer than the previous refrigerants that ammonia was banned for use aboard ships by some countries.
At the start of the 1990s it was discovered that these new "Chlorofluorocarbons" were eating away the ozone layer that surrounds the atmosphere of the earth. This layer protects the earth from the harmful effects of the ultraviolet (UV) rays from the sun. These UV rays have been linked to some skin cancers. In 1991, the International Maritime Organization (IMO) banned the use of Freons as a refrigerant on all new ships.
Today, many alternate refrigerants are in use. One, which is enjoying a comeback, is the previously banned ammonia. The high cost of some of the Freon replacements coupled with the fact that ammonia is readily available worldwide, and is environmental friendly, is insuring ammonia's place back aboard refrigerated ships.
In addition to the standard bulk refrigerated ships, today we have the refrigerated container ship. The Intermodal container has evolved to become the most innovative change in cargo handling in the history of the shipping industry. Its ability to move from one mode of transportation to another without having to unload its contents makes it not only fast but also reduces pilfering. These containers can either have their own refrigeration unit (gensets) attached or they are designed to be carried aboard special ships with refrigeration manifolds, which attach directly to portholes in the ends of the specially insulated containers. This last type is known as Conair.
Regardless of the type of refrigerant or its method of use, there is another hazard we in the Fire Service must be aware of when it comes to refrigeration. That hazard is the effect refrigerated atmospheres have on some of the deadly products of combustion. Normally during a fire and immediately after, most of the gasses given off by the fire will be heated by that fire and rise to ceiling level. If the fire area or adjoining areas are refrigerated, the smoke is rapidly cooled and becomes heavier than the air. This smoke and its products of incomplete combustion will now drop to the lower levels. Members operating in a refrigerated compartment, even with only a slight haze of smoke, will be subjected to higher concentrations of carbon monoxide (CO) at the floor level. (OSHA 2 in 2 out and mask policy is mandatory.)
Another feature has recently added a new problem aboard refrigerated ships. To delay the ripening of perishable fruits and vegetables during shipment the Controlled Atmosphere (CA) or Modified Atmosphere (MA) has been introduced. It has been discovered that the ripening process of these fruits and vegetables can be significantly slowed when the product is exposed to a nitrogen-enriched atmosphere. The benefit of this is that the product can be picked in a more ripe condition. That will equate into a better tasting fruit or vegetable. This will also reduce the amount of artificial treatment the product must undergo to make it appear ripe.
What this means to the Fire Service is that these compartments will have oxygen deficient environments. You cannot enter these areas, or adjoining areas, without the aid of self-contained breathing apparatus (SCBA). Oxygen meters and gas detection units should be used prior to entry of any enclosed cargo space aboard ship. (Observe all OSHA Confined Space guidelines).
To save costs, the Nitrogen used aboard ship is usually generated on the ship. This poses another hazard. A waste product of this Nitrogen generation process is a gas called "Permeate". It has an oxygen content of approximately 35% and is therefore a strong oxidizing agent. (Normal air contains 21% oxygen) An oxidizing agent will greatly accelerate chemical reactions such as corrosion and combustion. In the course of normal operations, the Permeat is disposed of by discharging into the open air when the ship is underway. This discharge must be located a safe distance (min 5 meters) from the intakes of any combustion engines, such as the refrigeration units (Gensets) located on some containers. If the ship is in port and on fire, you might want to insure that this Permeat is not getting to the fire.
Refrigeration has enabled the shipping industry to provide us with many products that would otherwise not be available in certain climates. It is no longer a convenience but has long ago become necessary for life, as we know it. Under normal conditions, and when handled carefully refrigeration does not present a problem.
We in the Fire Service very rarely operate under normal conditions and quite often are called in when an accident or fire has already ruptured refrigerant lines. Once again we will be entering an area from which other (more sane?) people are running. Be sure you know the dangers and are properly equipped for them. Shipboard firefighting presents many unique hazards and challenges for the Fire Service. Only through training and familiarization can we expect to operate aboard a ship with any degree of safety.
1. Handbook of Fire Protection 4th. edition, Pg. 2-17 , The National Fire Protection Association
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