Sulphuric Acid Plant Safety - Sulphur
November 4, 2003
Introduction
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)
Flammability
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.
Fire Fighting
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.
Burn Hazard
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.
Hydrogen
Sulphide
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.
Respiratory Protection
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.
Eye/Face
Protection
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.
Protective Clothing
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.
Safety Signs
| 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. |
 |
