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Sulphuric Acid Plant Safety - Sulphur
November 4, 2003
Safety in handling sulphur, whether as a solid or liquid, requires recognition of and adequate precautions against three possible dangers:
Sulphur is a flammable substance and its vapours and dust may be explosive
Sulphur in its molten state is a burn hazard
Sulphur may generate hazardous amounts of hydrogen sulphide gas (H2S)
If ignited by spark or flame, sulphur will burn in air, yielding acrid fumes of sulphur dioxide (SO2). Various investigators have reported spontaneous ignition temperatures for molten pure sulphur in still air which vary from 232°C to 260°C (450°F to 500°F). The flash point of pure sulphur, as determined by the modified Cleveland open cup method and others, has been reported by various investigators at values from 188°C to 207°C (370°F to 405°F). It is agreed that the presence of hydrocarbon impurities in the sulphur will decrease these reported values. The minimum reported value for the flash point of dark crude sulphur is 168°C (335°F).
Sulphur dust suspended in air is readily ignited by flame, static electricity or friction spark. The dust is characterized by a very low ignition point of 190°C (374°F) compared to other combustible dusts. Dust containing 25% or more elemental sulphur may be almost explosive as pure sulphur. Explosive mixtures can also be formed if sulphur is contaminated with chlorides, nitrates or other oxidizing agents. Sulphur is an excellent electrical insulator and under the right conditions will readily pick up static electricity which if discharged can be a source of ignition. The use of spark resistant tools and nonferrous conveyor parts is recommended to minimize sparks when handling solid sulphur.
Where there is a potential for dust to accumulate or be generated the area must be designated with the appropriate hazardous area classification. Electrical equipment in this area must be suitable for the hazardous area classification.
If a fire occurs in a closed tank or pit containing molten sulphur it can be extinguished by closing all vents and air inlets. However, the tank or pit may become very hot before the fire is extinguished. A more effective way to extinguish a fire is to use steam. 'Snuffing' steam is admitted to the vapour space of the tank and displaces the oxygen in the tank thus starving the fire of oxygen. The system must be properly engineered to ensure steam is distributed thoughout the vapour space.
Small fires in melting pits can often be extinuguished by splashing liquid sulphur to smother the fire.
Spraying water onto the fire may cause the generation of a large amount of steam as the water hits the surface of the hot sulphur. The sudden generation of steam in an enclosed space may result in overpressurization of the tank.
If a fire occurs in a bulk solid sulphur storage pile or hopper, a fine spray or fog of water is the most satisfactory fire extinguishing agent.
As a safety precaution, it is recommended that a water line with hose and fog nozzle should be located where it can be used to extinguish fires in the sulphur storage and melting areas.
Carbon dioxide fire extinguishers can also be employed in fighting sulphur fires.
Molten sulphur is typically maintained at a temperature of 140°C (284°F) so improper handling of molten sulphur may result in burns to personnel. First degree burns can result from splashes of liquid sulphur on skin or clothing. The sulphur will quickly solidify but it should not be removed. The affected area should be immerse in cold water for at least 20 minutes and the patient treated for shock. Medical attention should be obtained immediately.
Most of the world's sulphur is produced from the treatment of sour gases found in refinery and natural gas plants. When solid sulphur is melted, a small amount of hydrogen sulphide gas may be released. Hydrogen sulphide is a toxic, as well as flammable gas.
Sulphur is essentially non-toxic but dust respirators should be worn for the comfort of workers. In case of emergencies, breathing apparatus suitable for sulphur dioxide should be available in the area. Sulphur dioxide will be produced during a sulphur fire.
In areas where solid sulphur is being handled, dust tight goggles should be worn. In areas where molten sulphur is present, safety glasses with side shields should be worn. A face shield may also be necessary.
The use of fire-retardant clothing is recommended. Clothing should be kept clean and free of dust. Heat resistant gloves should be worn in molten sulphur areas.
From a transportation perspective, sulphur is classified as a flammable solid and the following sign will be displayed on the shipment. The sign may also be displayed in bulk storage areas. From a transportation perspective, sulphur can also be classified as a Class 9 material.