SEFA
Encyclopedia
The SEFA is a make of backpack
industrial breathing set formerly made by Sabre Safety. It is an oxygen rebreather
. "SEFA" is an acronym for "Selected Elevated Flow Apparatus".
and a front panel for talking through. Its breathing tubes are 22 inches long, and face forward as they come off the backpack casing.
Its full duration on a filling is 2 hours. It does not have a demand valve or electronic
parts, and in theory this would be fewer parts to suffer from failures. It is not designed for scuba diving
, but can be used for short shallow submersion such as going through short flooded sections of underground passages. Its casing, to keep grit and stones out of its working, is completely sealed, except for a large vent panel covered with metal mesh, and holes for the oxygen cylinder's on/off valve and the cylinder pressure gauge. Its oxygen flow can be set to 5 or 10 liters/minute. Its intended absorbent is a special make called SefaSorb, which is mostly calcium hydroxide
.
As usual, the absorbent makes the breathing gas in circuit hot as it absorbs carbon dioxide
. This would be welcome while scuba diving in cold water, but in warm air in a deep mine would be unwelcome. To try to get rid of that heat, the breathing gas is passed through a damp chamber, so the damp will absorb some heat as it evaporates, as in some air conditioning
units. It is not very effective, in normal use the breathing air temperature of the SEFA will rapidly exceed 45°C, and more under heavy work. Being made almost entirely from metal, the SEFA does dissipate its thermal load relatively easily.
The SEFA was not a spectacular success, being exported to very few countries. It was a case of "too little too late", a 2-hour duration set entering a market already mainly dominated by the German Draeger BG174 (with a 4 hour duration). The SEFA was difficult to service, most parts could only be removed with special tools, and reassembly could be problematic. Testing a SEFA often caused extra work for the operator, as several small leaks in the breathing loop would inevitably arise after servicing and need troubleshooting
before the set could be put back in use. Compared to the modern day Draeger PSS BG4 sets, and the American BioPakhttp://www.biopak240r.com/, which can all be completely stripped and reassembled by hand without using tools, the SEFA is less convenient to maintain.
The SEFA is still in use in the mining industry in India, and up until 2006 was still being used at the Porgera Gold Mine
in Papua New Guinea
.
industry for a new make of mines rescue breathing set with longer duration for bulk than an open-circuit set. They were made from 1989 to 2004. Making them stopped because of declining demand because of the decline of the British coal mining industry. They are no longer official issue because of lack of availability of spare parts. The British coal industry, when needing rebreather
s, now uses a German rebreather made by Draeger.
, because:-
techniques in open air without any gas
hazard in the area.
Backpack
A backpack is, in its simplest form, a cloth sack carried on one's back and secured with two straps that go over the shoulders, but there can be exceptions...
industrial breathing set formerly made by Sabre Safety. It is an oxygen rebreather
Rebreather
A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...
. "SEFA" is an acronym for "Selected Elevated Flow Apparatus".
Description
It is in a shiny backpack stainless steel sheet casing with rounded corners and edges, 16 inches wide, 21½ inches high, 6½ inches front to back. It has two wide corrugated breathing tubes leading to a fullface mask which has an inner orinasal maskOrinasal mask
An orinasal mask is a breathing mask that covers the mouth and the nose only. It may occur independently, as an oxygen mask, or on some anaesthetic apparatuses, or it may occur inside a fullface mask on a scuba set or an industrial breathing set to reduce the amount of dead space...
and a front panel for talking through. Its breathing tubes are 22 inches long, and face forward as they come off the backpack casing.
Its full duration on a filling is 2 hours. It does not have a demand valve or electronic
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
parts, and in theory this would be fewer parts to suffer from failures. It is not designed for scuba diving
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
, but can be used for short shallow submersion such as going through short flooded sections of underground passages. Its casing, to keep grit and stones out of its working, is completely sealed, except for a large vent panel covered with metal mesh, and holes for the oxygen cylinder's on/off valve and the cylinder pressure gauge. Its oxygen flow can be set to 5 or 10 liters/minute. Its intended absorbent is a special make called SefaSorb, which is mostly calcium hydroxide
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...
.
As usual, the absorbent makes the breathing gas in circuit hot as it absorbs carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. This would be welcome while scuba diving in cold water, but in warm air in a deep mine would be unwelcome. To try to get rid of that heat, the breathing gas is passed through a damp chamber, so the damp will absorb some heat as it evaporates, as in some air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
units. It is not very effective, in normal use the breathing air temperature of the SEFA will rapidly exceed 45°C, and more under heavy work. Being made almost entirely from metal, the SEFA does dissipate its thermal load relatively easily.
The SEFA was not a spectacular success, being exported to very few countries. It was a case of "too little too late", a 2-hour duration set entering a market already mainly dominated by the German Draeger BG174 (with a 4 hour duration). The SEFA was difficult to service, most parts could only be removed with special tools, and reassembly could be problematic. Testing a SEFA often caused extra work for the operator, as several small leaks in the breathing loop would inevitably arise after servicing and need troubleshooting
Troubleshooting
Troubleshooting is a form of problem solving, often applied to repair failed products or processes. It is a logical, systematic search for the source of a problem so that it can be solved, and so the product or process can be made operational again. Troubleshooting is needed to develop and...
before the set could be put back in use. Compared to the modern day Draeger PSS BG4 sets, and the American BioPakhttp://www.biopak240r.com/, which can all be completely stripped and reassembled by hand without using tools, the SEFA is less convenient to maintain.
The SEFA is still in use in the mining industry in India, and up until 2006 was still being used at the Porgera Gold Mine
Porgera Gold Mine
The Porgera Gold Mine is a large gold and silver mining operation in Enga province, Papua New Guinea , located at the head of the Porgera Valley. The mine is situated in the rain forest covered highlands at an altitude of 2,200 to 2,700 m, in a region of high rainfall, landslides, and frequent...
in Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
.
History
It was being designed from 1985 onwards in response to demands from the British coal miningCoal mining
The goal of coal mining is to obtain coal from the ground. Coal is valued for its energy content, and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production. In the United States,...
industry for a new make of mines rescue breathing set with longer duration for bulk than an open-circuit set. They were made from 1989 to 2004. Making them stopped because of declining demand because of the decline of the British coal mining industry. They are no longer official issue because of lack of availability of spare parts. The British coal industry, when needing rebreather
Rebreather
A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...
s, now uses a German rebreather made by Draeger.
Not for scuba diving
It is not intended for scuba divingScuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
, because:-
- It is not designed to resist seawaterSeawaterSeawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
corrosionCorrosionCorrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
. - When a diver with a SEFA comes out of the water, a large pool of water would be held in the bottom of its casing, due to lack of a bottom drain hole.
- The usual hazards of oxygen rebreather diving would apply.
Images
When photographed these sets were being used without their internal parts during a demonstration of rescueRescue
Rescue refers to responsive operations that usually involve the saving of life, or prevention of injury during an incident or dangerous situation....
techniques in open air without any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
hazard in the area.