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Pyrotechnics Industry

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Adapted from 3rd edition, “Encyclopaedia of Occupational Health and Safety”.

The pyrotechnics industry may be defined as the manufacture of pyrotechnic articles (fireworks) for entertainment, for technical and military use in signalling and illumination, for use as pesticides and for various other purposes. These articles contain pyrotechnic substances made up of powders or paste compositions which are shaped, compacted or compressed as required. When they are ignited, the energy they contain is released to give specific effects, such as illumination, detonation, whistling, screaming, smoke formation, smouldering, propulsion, ignition, priming, shooting and disintegration. The most important pyrotechnic substance is still black powder (gunpowder, consisting of charcoal, sulphur and potassium nitrate), which may be used loose for detonation, compacted for propulsion or shooting, or buffered with wood charcoal as a primer.

Processes

Raw materials used in the manufacture of pyrotechnics must be very pure, free from all mechanical impurities and (above all) free from acid ingredients. This also applies to subsidiary materials such as paper, pasteboard and glue. Table 1 lists common raw materials used in pyrotechnics manufacture.

Table 1. Raw materials used in the manufacture of pyrotechnics

Products

Raw materials

Explosives

Nitrocellulose (collodion wool), silver fulminate, black powder
(potassium nitrate, sulphur and charcoal).

Combustible materials

Acaroid resin, dextrine, gallic acid, gum arabic, wood, charcoal,
rosin, lactose, polyvinyl chloride (PVC), shellac, methylcellulose,
antimony sulphide, aluminium, magnesium, silicon, zinc,
phosphorus, sulphur.

Oxidizing materials

Potassium chlorate, barium chlorate, potassium, perchlorate, barium
nitrate, potassium nitrate, sodium nitrate, strontium nitrate, barium
peroxide, lead dioxide, chromium oxide.

Flame-tinting materials

Barium carbonate (green), cryolite (yellow), copper, ammonium
sulphate (blue), sodium oxalate (yellow), copper carbonate (blue),
copper acetate arsenite (blue), strontium carbonate (red), strontium
oxalate (red). Dyes are used to produce coloured smoke,
and ammonium chloride to produce white smoke.

Inert materials

Glyceryl tristearate, paraffin, diatomaceous earth, lime, chalk.

 

After being dried, ground and sifted, the raw materials are weighed and mixed in a special building. Formerly they were always mixed by hand but in modern plants mechanical mixers are often used. After mixing, the substances should be kept in special storage buildings to avoid accumulations in workrooms. Only the quantities required for the actual processing operations should be taken from these buildings into the workrooms.

The cases for pyrotechnic articles may be of paper, pasteboard, synthetic material or metal. The method of packing varies. For example, for detonation the composition is poured loose into a case and sealed, whereas for propulsion, illumination, screaming or whistling it is poured loose into the case and then compacted or compressed and sealed.

Compacting or compressing formerly was done by blows from a mallet on a wooden “setting-down” tool, but this method is rarely employed in modern facilities; hydraulic presses or rotary lozenge presses are used instead. Hydraulic presses enable the composition to be compressed simultaneously in a number of cases.

Illumination substances are often shaped when wet to form stars, which are then dried and put into cases for rockets, bombs and so on. Substances made by a wet process must be well dried or they may ignite spontaneously.

Since many pyrotechnic substances are difficult to ignite when compressed, the pyrotechnic articles concerned are provided with an intermediate or priming ingredient to ensure ignition; the case is then sealed. The article is ignited from the outside by a quick-match, a fuse, a scraper or sometimes by a percussion cap.

Hazards

The most important hazards in pyrotechnics are clearly fire and explosion. Because of the small number of machines involved, mechanical hazards are less important; they are similar to those in other industries.

The sensitivity of most pyrotechnic substances is such that in loose form they may easily be ignited by blows, friction, sparks and heat. They present fire and explosion risks and are considered as explosives. Many pyrotechnic substances have the explosive effect of ordinary explosives, and workers are liable to have their clothes or body burned by sheets of flame.

During the processing of toxic substances used in pyrotechnics (e.g., lead and barium compounds and copper acetate arsenite) a health hazard may be present from inhalation of the dust while weighing and mixing.

Safety and Health Measures

Only reliable persons should be employed in the manufacture of pyrotechnic substances. Young persons under 18 years of age should not be employed. Proper instruction and supervision of the workers are necessary.

Before any manufacturing process is undertaken it is important to ascertain the sensitivity of pyrotechnic substances to friction, impact and heat, and also their explosive action. The nature of the manufacturing process and permissible quantities in the workrooms and the storage and drying buildings will depend on these properties.

The following fundamental precautions should be taken in the manufacture of pyrotechnic substances and articles:

  • The buildings in the non-hazardous part of the undertaking (offices, workshops, eating areas and so on) should be sited well away from those in the hazardous areas.
  • There should be separate manufacturing, processing and storage buildings for the different manufacturing processes in the hazardous areas and these buildings should be situated well apart
  • The processing buildings should be divided up into separate workrooms.
  • The quantities of pyrotechnic substances in the mixing, processing, storage and drying buildings should be limited.
  • The number of workers in the different workrooms should be limited.

 

The following distances are recommended:

  • between buildings in the hazardous areas and those in the non-hazardous areas, at least 30 m
  • between the various processing buildings themselves, 15 m
  • between mixing, drying and storage buildings and other buildings, 20 to 40 m depending on the construction and the number of workers affected
  • between different mixing, drying and storage buildings, 15 to 20 m.

 

The distances between working premises may be reduced in favourable circumstances and if protective walls are built between them.

Separate buildings should be provided for the following purposes: storing and preparing raw materials, mixing, storing compositions, processing (packing, compacting or compressing), drying, finishing (gluing, lacquering, packing, paraffining, etc.), drying and storing the finished articles, and storing black powder.

The following raw materials should be stored in isolated rooms: chlorates and perchlorates, ammonium perchlorate; nitrates, peroxides and other oxidizing substances; light metals; combustible substances; flammable liquids; red phosphorus; nitrocellulose. Nitrocellulose must be kept wet. Metal powders must be protected against moisture, fatty oils and grease. Oxidizers should be stored separately from other materials.

Building design

For mixing, buildings of the explosion-venting type (three resistant walls, resistant roof and one explosion-vent wall made of plastic sheeting) are the most suitable. A protective wall in front of the explosion-vent wall is advisable. Mixing rooms for substances containing chlorates should not be used for substances containing metals or antimony sulphide.

For drying, buildings with an explosion-vent area and buildings covered with earth and provided with an explosion-vent wall have proved satisfactory. They should be surrounded by an embankment. In drying houses a controlled room temperature of 50 ºC is advisable.

In the processing buildings, there should be separate rooms for: filling; compressing or compacting; cutting off, “choking” and closing the cases; lacquering shaped and compressed pyrotechnic substances; priming pyrotechnic substances; storing pyrotechnic substances and intermediate products; packing; and storing packed substances. A row of buildings with explosion-vent areas has been found to be best. The strength of the intermediate walls should be suited to the nature and quantity of the substances handled.

The following are basic rules for buildings in which potentially explosive materials are used or present:

  • The buildings should be single-storied and have no basement.
  • Roof surfaces should afford sufficient protection against the spread of fire.
  • The walls of the rooms must be smooth and washable.
  • Floors should have a level, smooth surface without gaps. They should be made of soft material such as xylolith, asphalt free from sand, and synthetic materials. Ordinary wood floors should not be used. The floors of dangerous rooms should be electrically conductive, and the workers in them should wear shoes with electrically conductive soles.
  • The doors and windows of all buildings must open outwards. During working hours doors should not be locked.
  • The heating of buildings by open fires is not permissible. For heating dangerous buildings, only hot water, low-pressure steam or dust-tight electrical systems should be used. Radiators should be smooth and easy to clean on all sides: radiators with finned pipes should not be used. A temperature of 115 ºC is recommended for heating surfaces and pipes.
  • Workbenches and shelves should be made of fire-resistant material or hard wood.
  • The work, storage and drying rooms and their equipment should be regularly cleaned by wet wiping.
  • Workplaces, entrances and ways of escape must be planned in such a way that rooms can be quickly evacuated.
  • As far as practicable, workplaces should be separated by protective walls.
  • Necessary stocks should be stored safely.
  • All buildings should be equipped with lightning conductors.
  • Smoking, open flames and the carrying of matches and lighters within the premises must be prohibited.

 

Equipment

Mechanical presses should have protective screens or walls so that if fire breaks out the workers will not be endangered and the fire cannot spread to neighbouring workplaces. If large quantities of materials are handled, presses should be in isolated rooms and operated from outside. No person should stay in the press room.

Fire-extinguishing appliances should be provided in sufficient quantity, marked conspicuously and checked at regular intervals. They should be suited to the nature of the materials present. Class D fire extinguishers should be used on burning metal powder, not water, foam, dry chemical or carbon dioxide. Showers, woollen blankets and fire-retardant blankets are recommended for extinguishing burning clothing.

Persons who come into contact with pyrotechnic substances or are liable to be endangered by sheets of flame should wear proper fire- and heat-resistant protective clothing. The clothing should be de-dusted daily at a place appointed for the purpose to remove any contaminants.

Measures should be taken in the undertaking to provide first aid in case of accidents.

Materials

Dangerous waste materials with different properties should be collected separately. Waste containers must be emptied daily. Until it is destroyed, collected waste should be kept in a protected place at least 15 m from any building. Defective products and intermediate products should as a rule be treated as waste. They should only be reprocessed if to do so does not create any risks.

When materials injurious to health are processed, direct contact with them should be avoided. Harmful gases, vapours and dusts should be effectively and safely exhausted. If the exhaust systems are inadequate, respiratory protective equipment must be worn. Suitable protective clothing should be provided.

 

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