CHEMICAL SAFETY TRAINING MODULES

PART V: MAJOR HAZARD CHEMICALS

There have been several of major industrial disasters related to the use of chemicals. Although they are individual accidents, different in the way in which they happened and the chemicals that were involved, they have one common feature: they were uncontrolled, involving fires, explosions or the release of toxic substances that either resulted in the death and injury of large numbers of people inside and outside of the factory or caused extensive damage to the property and the environment.

Accidents involving major hazards could start with

• leakage of a flammable substance, mixing of the substance with air, formation of a flammable vapour cloud and drifting of the cloud to a source of ignition leading to a fire or an explosion.
• leakage of toxic substances, formation of a toxic vapour cloud and drifting of the cloud.

These clouds would directly affect the site as well as possibly the surrounding populated areas.

In the case of flammable substances the greatest danger arises from sudden massive escape of volatile liquids or gases. If the cloud were ignited, the effects of combustion would depend on many factors, such as wind speed and the extent to which the cloud was diluted. The area affected would generally be limited to a few hundred metres from the site.

Much larger areas can be dangerously affected in a sudden release or by very large quantities of toxic materials. In favorable conditions such a cloud can still contain lethal concentrations of toxic chemicals several kilometers from the accident site. The extent of casualty depends on the number of people in the path of the cloud and on the efficiency of emergency arrangements, for example, evacuation before the cloud reaches the populated areas.

The effect can also migrate into other factories situated nearby and containing flammable, reactive or toxic chemicals, escalating the disaster. This is sometimes referred to as the `domino effect'.

Not only does the cloud itself pose a health hazard, but the fires cause depletion of oxygen and fumes generated by the fire may contain toxic gases.

Chlorine and ammonia are the toxic chemicals most commonly used in quantities large enough to pose a major hazard. Both have a history of major accidents. There are also other chemicals which, although used in smaller quantities, should be handled with particular care because of their higher toxicity.

An industrial accident classified as a `major hazard' leads to tighter control handling that substance or process, more specific than that applied in the normal factory operations. This is in order to protect both workers and outside people, to avoid economical losses to the factory and damage to the environment.

The first step in a systematic approach is to identify the installations susceptible to a `major hazard'. For this purpose, in EU countries a Directive has been in use since 1984.

This Directive sets certain criteria based on the toxic, flammable and explosive properties of the chemicals. For the selection of specific industrial activities which involve a `major hazard' risk, a list of substances is provided with limit amounts related to the potential hazard. The list contains 180 toxic substances with the limits varying from 1 kg for extremely toxic substances to 50 000 tons for highly flammable liquids.

Criteria for Major Hazard Installation

1.1 Very Toxic (Categories 1 and 2)

1.2 Toxic substances (Category 3)

1.3 Classification can also be done by determining the acute toxicity in animals, expressed in LD₅₀ or in LC₅₀ values and using the following limits. See Table 1.

Table 1. Acute toxicity criteria for major hazard installations

2. Flammable substances

2.1 Gases which form flammable mixtures with air

2.2 Highly or extremely flammable liquids with flash points lower than 21^oC

2.3 Flammable liquids with flash points lower than 55^oC

3. Substances which may explode when in contact with a source of ignition or which are more sensitive to shock and friction than dinitrobenzene

The industrial activities creating the risk of a major hazard cannot be restricted to defined sectors. Experience has shown that incidences with potential major hazard risk are in installations with the following activities:

• petrochemical works and refineries
• chemical works and chemical production plants
• LPG (Liquid Petroleum Gas) storage and terminals
• stores and distribution centres of chemicals
• large fertilizer stores
• factories handling explosives
• works in which chlorine is used in bulk quantities

Table 2 is a shortened list of Major Hazard Chemicals to be used as a guide and in set priorities . Priorities can also be set within the factory to identify the most hazardous areas in the production activities.

Table 2. A list of priority chemicals used in identifying major hazard installations.

CHLORINE

1. Cases

Chlorine poisoning in Sri Lanka

Chlorine poisoning happened to a 37-year-old mechanical supervisor at a water purification plant in Sri Lanka while he was working with the main cylinder valve. He was exposed to chlorine fumes for a few seconds as he was running in and out to stop the gas flow. He started to have an intense feeling of suffocation and tightness of chest, coughing, intolerable irritation of eyes and mouth, headache and stomach problems. He still had symptoms 27 days after the incident.

Transport accident

A massive chlorine release as a result of a tank leak in a car carrying chlorine took place in Norway. Approximately 7-8 tons of chlorine gas formed a 10 km long cloud which covered the valley. A total of 85 people, from 6 months to 82 years of age were hospitalized, and out of those 3 died.

2. Properties

Chlorine is a greenish-yellow gas with a pungent odour. It is heavier than air and the chlorine cloud tends to spread along the ground. It can fill cellars or flow into subway tunnels as it did in an accident in New York leading to the hospitalization of 208 persons.

Chlorine is chemically very active. Dry chlorine at ambient temperatures reacts directly with many materials including metals. Dry chlorine does not attack steel and it is supplied commercially in steel containers in liquid form under pressure.

As liquid chlorine evaporates, at boiling point (-34^oC), one volume unit of liquid forms 457 volume units of gas.

Traces of moisture in chlorine lead to rapid corrosion of steel, copper and nickel. Chlorine react vigorously with organic compounds including mineral oils and greases. Mixtures of chlorine and hydrogen gases are explosive.

Chlorine dissolves in water at a rate of 6.5 g of chlorine to one litre of water at ambient temperature. The solution is acidic and corrosive, and it has oxidizing, bleaching and germicidal properties. The water solution in a process should be kept above a temperature of 9.6^oC in order to avoid blockages as a result of formation of solid chlorine hydrate.

The reactivity of chlorine strongly limits the choice of construction materials when planning pipes and installations. A system made of steel must be dry before allowing chlorine to enter in it. Titanium is a satisfactory construction material at temperatures well below 100^oC provided that the moisture level is kept high. Titanium is resistant only to wet chlorine, and consideration should be given to a possible fault where dry chlorine could come into contact with the titanium.

Other materials which are resistant to the attack of both wet and dry chlorine gas at ambient temperatures include glass, stoneware, porcelain and some plastics.

Where chlorine is part of the product, such as chlorinated hydrocarbon solvents, it may be liberated in a fire or when in contact with incompatible chemicals giving off hazardous gases and fumes.

The recommended exposure limit, Threshold Limit Value (TLV), for chlorine is 1 part per million (ppm), a concentration which is at the limit of odour detection.

The Short Term Exposure Limit (STEL) is 3 ppm.

Liquid chlorine causes frost burns and is corrosive to human tissue.

Chlorine is a respiratory irritant. Exposure to chlorine at levels of around 15 ppm leads to irritation of the mucous membranes of the eyes and nose, and especially of the throat and lungs.

The gas becomes fatal at concentrations of 100-150 ppm with an exposure duration of 5-10 minutes.

The accidental instantaneous release of 10 tons of chlorine may result in a maximum concentration of 140 ppm at a distance of 2 kilometres downwind from the source and 15 ppm at a distance of 5 kilometres (under normal non-inversion weather conditions).

A chlorine vessel of 1 ton releasing liquid at full flow through an open valve will be empty in about 10 minutes, and a cylinder in far less time.

Table 3. Effects of chlorine gas concentrations on people (1 ppm = 3 mg/m³)

Gas filters are effective against chlorine only at low concentrations. Filter type B can be used for concentrations below 0.1 % by volume. If the colour of chlorine gas is visible the concentration has exceeded the recommended exposure limit mentioned above (TLV).

The EU classification for chlorine is toxic, T, and dangerous to the environment, N, with risk phrases and safety phrases:

R23: Toxic by inhalation.

R36/37/38: Irritating to eyes, respiratory system and skin.

R50: Very toxic to the aquatic organisms.

S1/2: Keep locked up and out of reach of children.

S9: Keep container in a well-ventilated place.

S45: In case of accident or if you feel unwell, seek medical advice immediately (show the label where possible).

S61: Avoid release to the environment. Refer to special instructions/Safety Data Sheets.

3. Use of chlorine

Chlorine is widely used as part of many everyday products. It is used world wide for purifying drinking-water and for wastewater treatment. Most of the chlorine is used in the manufacture of chlorinated compounds, in sanitation, pulp bleaching and textile processing, and in the pesticide industry.

It is also used in dyestuffs and in petroleum production. It is found in medicines, antiseptics, insecticides, foodstuffs, solvents, paints, plastics and many other consumer products.

4. Transport of chlorine

During transportation, chlorine has an UN identification number 1017. It is placed in Class 2.3 (toxic gas) with subsidiary danger classification of Class 8. (corrosive substance). Containers and cylinders should have the corresponding symbols and the transporting vehicle should have visible placards.

Where chlorine is used in large quantities, it is subject to several notification requirements, standards, advice, restrictions, operational codes and maintenance procedures because of the potential risks involved in its storage and handling.

The advice should be used to develop emergency plans and routine maintenance checklists, taking into account the special features of the specific installation.

AMMONIUM NITRATE FERTILIZERS

1. Properties

Fertilizers are materials that are introduced to the soil to obtain plentiful and stable harvest crops. They are manufactured for the purpose, they may be by-products from chemical industry processes, or they may be natural materials, such as dung, guano, bone-meal, peat. Industrially manufactured fertilizers have largely replaced by-products and natural organic materials. The segment of agrochemicals has grown to be one of the major areas of chemical industry.

Today's food and animal feedstuff production depends greatly on the plant nutrients added to the soil. The principal elements required are nitrogen, phosphorus and potassium. Other elements needed in smaller quantities, including trace elements, are relevant to growth, such as calcium, magnesium, sulphur, iron, zinc, manganese, copper, molybdenum, boron, and iodine. Plants cannot consume the pure chemical elements, some of them are even harmful. For example, phosphorus in elemental form is toxic to plants but useful when available in a suitable compound.

Nitrogen is one of the macro-nutrients, it is needed in relative large quantities. Most plants cannot consume nitrogen as gas although it is present in sufficient amounts as a component of the air we breath. It can be supplied in the form of chemical compounds, often as urea or ammonium nitrate. Compounds may carry more than one essential nutrient to plants in water-soluble combinations. For example, ammonium phosphate contains nitrogen and phosphorus.

Table 4. Nitrogen supply in various fertilizers

* FAO data of nitrogen containing fertilizers, 1976-77

Ammonium nitrate may be produced from ammonia and nitric acid as raw materials. Nitric acid is neutralized with ammonia to form a solid salt. Ammonium nitrate is a colourless, crystalline solid, melting at 170^oC, and decomposing when heated above 210^oC. Commercially it is distributed in the form of crystals, beads, pellets or flakes. 95% of the fertilizers used in EU countries are in solid form.

Ammonium nitrate is very soluble in water. One part of water dissolves about two parts of the nitrate by weight. Ammonium nitrate is not sensitive to friction or impact in conditions encountered in normal handling of limited quantities, but may explode if heated in confined spaces or on severe shock. Impurities, specifically organic matter, increase the risk of detonation. When heated to decomposition, for example by fire, ammonium nitrate emits toxic and corrosive nitrogen oxides which may colour the fumes from yellow to brown. Mixtures of ammonium nitrate and several substances may lead to decomposition or explosion. Examples of such compounds are powdered metals, chromium or copper salts, sulphur, alkalis or acids, nitrites and chlorates.

Ammonium nitrate does not burn but decomposes in contact with several materials enhancing the burning of combustibles. Pellets containing ammonium nitrate and charcoal (10%) are used as explosives. They ignite when heated to 170^oC or at lower temperatures if impurities, such as rust or zinc oxide powder, are present. Ammonium nitrate and aluminum powder mixtures are used as a commercial explosive called Ammonal, but sugar syrup mixed with this salt is also explosive. Mixing operations with other fertilizer materials using concentrated solutions, such as urea, have lead to explosions. Hot water solutions containing more than 50% of ammonium nitrate can decompose explosively, especially if the solution contains catalyzing impurities, such as ammonium chloride or iron chloride (this may be possible during sea transport).

These properties of ammonium nitrate determine commercial use: it is produced in bulk amounts for fertilizers but it is also as an ingredient in blasting explosives.

Fertilizers are divided to two categories:

• fertilizers containing more than 28% of nitrogen by weight
• fertilizers containing not more than 28% of nitrogen by weight

The grouping specifies the requirement for transport and storage.

Those fertilizers that contain not more than 28% of nitrogen are not regarded as explosives under normal conditions of use and handling. Decomposition, however, produces toxic and corrosive gases.

2. Health effects

Ammonium nitrate dust is irritating to the respiratory tract and may lower the blood pressure.

Ammonium nitrate is often a part of formulations, and the exposure of the other components of the mixtures influence the health effects.

3. Occupational exposure

The hazards related to ammonium nitrate fertilizers can be grouped into those in manufacturing, storage, transport and application to the soil.

Ammonium nitrate is manufactured by neutralizing nitric acid with ammonia. The reaction produces large amounts of heat and is usually carried out in pressure vessels, neutralizers, and in a closed system to enable recovery of steams and gases. The neutralized solution is concentrated to a melt in a concentrator. The final solid is in the form of pearls or granules which are conditioned by coating to reduce the moisture absorption.

During these processes toxic and corrosive gases, such as acid fumes, nitrogen oxides and ammonia, may be released into the workplace atmosphere. Specifically, this may take place when inspection lids of the processing plant are opened and when the plant or reactors are cleaned or repaired. The ventilation system may not work satisfactorily, the air ducts of exhaust systems may clog with moist dust or reactor material.

Packaging and moving of solid compounds may raise dust of materials used in the processes. Some raw materials used in mixing formulations may contain free silica, which may cause health problems in the respiratory tract, including pneumoconiosis.

The explosive properties of ammonium nitrate must be considered during transport.

Planning the storage area should take into account the fact that the storage and finished fertilizers are associated with ageing processes which slowly release gases to the surroundings. Some of these gases are toxic and corrosive, also corroding construction materials.

4. Safety measures

Spilt ammonium nitrate should be collected carefully, water solutions wiped up and the remainder washed away with water. Under NO circumstances should the spill be absorbed to combustible materials, such as sawdust or paper.

The cleanliness of the storage area and used tools, including shovels, is important in storage and handling as combustible materials, such as oil spillage, and many other chemicals are liable to trigger reaction with ammonium nitrate.

NO SMOKING signs should be placed wherever ammonium nitrate is stored or handled. Fire-fighting equipment should be made available. Large, flooding amounts of water are recommended for fires involving ammonium nitrate. Chemical fire extinguishers or foams are not recommended.

Many countries have limits on the total amount of stored ammonium nitrate in a single store. In the European Union countries this limit is set at 1250 tons in a general storage area and 10 000 tons in an industrial storage area, such as a fertilizer factory.

5. Storage, transport

United Nations Committee of Experts for Transport of Dangerous Goods has assessed and divided ammonium nitrate products under various titles according to the type of danger.

Table 5. Classification of ammonium nitrate for transport

5.1. Storage of fertilizers containing more than 28% of nitrogen by weight

This type of formulations should be kept in dedicated well-ventilated buildings made of non-combustible materials such as concrete or steel. Sheets or joints made of galvanized metal are not recommended, as ammonium nitrate corrodes these materials. The storage area may also be outside on a concrete base. The bins and silos for bulk storage in the farm could be made of reinforced glass fibre plastic. Special concern should be paid to the drains to prevent the possible release of molten state ammonium nitrate.

Contact with heat and with materials that may react in contact with ammonium nitrate should be prevented. On farms ammonium nitrate should be stored away from hay, straw and feeding stuffs and not in the same area as flammable liquids, fuels and oil.

Stacks should be built to leave a space at least 1 metre wide around the stack, and a similar distance to the roof, electrical equipment and light bulbs. Vehicles and forklift trucks should not be left unattended in the storage area.

Bags should be completely sealed when packed and equipped with microvents to prevent ballooning effect. Pallets can be used. The bag should be made of water- and oil-resistant material; paper packaging is NOT recommended. Ammonium nitrate should never be mixed with other products in the same stack.

Special attention should be paid to spillage, damaged bags and contaminated ammonium nitrate. Spillage should be cleaned up promptly and contaminated material disposed safely. Small amounts of ammonium nitrate may be spread thinly on open ground, washing away with water if this is permitted by the authorities. The effluent should not enter directly to the drains, sewage system or water-ways.

Walls, floors, tools and equipment should be kept clean. The impregnation of pallets, ropes and covers by ammonium nitrate should prevented. Ammonium nitrate dissolves well into water, and also to wet materials.

Bulk storage should take place inside a building or in a silo. The risk of contamination of unpacked materials is inherently great. Entrance to this building should be restricted to authorized personnel only.

Precautions should be considered already at the planning of the storage site. Distances from other buildings or stored materials, electrical equipment and the means of moving the materials should be respected. Conveyor belts are recommended in moving unpacked ammonium nitrate.

5.2. Storage of fertilizers containing not more than 28% of nitrogen

This type of ammonium nitrate formulation may be stored outside and in a storage area with other products, provided that combustible materials and those which may react with ammonium nitrate are separated by a distance of 5 metres or by a fire-resistant wall.

6. Effects on the environment

Nitrate fertilizers are very soluble in water. They dissolve from fields into rain water, and amounts not used by the plants are flushed into waterways. They also fertilize aquatic plants, leading to uncontrolled increase of the vegetation: eutrophication. Nitrates may also enter the groundwater causing pollution.

LIQUEFIED HYDROCARBON GASES

Liquefied hydrocarbon gases are economical, important sources of energy. They are widely used both domestically, in agriculture and industry.

Liquefied Natural Gas (LNG) is extracted from the earth's crust, where it is often on top of oil deposits, but also forms large gas fields. Bore holes may be kilometers deep and the gas is there under pressure. Commercially available LNG contains over 95% of methane.

Liquefied Petroleum Gas (LPG) is obtained from crude oil in petroleum-processing plants. LPG may contain butane, propane, isobutane and unsaturated compounds with 3-4 carbon atoms. The main components in commercially available LPGs are butane and propane gases. A typical commercial mixture is 60:40 of butane and propane.

LPG is mainly consumed as fuel in various domestic (cooking gas) and industrial applications, although it is also widely used in aerosols as a propellant and in the chemical industry, for example, in the production of acetic acid, isobutane, and 1,3-butadiene. Not only butane and propane but also other gases, which may be liquefied, are separated in the crude oil refineries. Among these are unsaturated compounds such as ethylene, propylene and butylene, which are asphyxiants and weak anaesthetics. The first two have been used in medical surgery.

Liquefied petroleum gases are raw materials for various industrial products, such as solvents, plastics, resin, artificial fertilizers, fibres for textiles, rubber articles, detergents and carbon black for printing ink.

1. Properties

LPG and LNG are gases at normal temperatures and pressure. They are liquefied by pressurizing and by cooling. The liquids and gases are colourless and odourless but compounds with odour have been added to enable detection of leakages by smell. The vapour cloud from spilled liquid may have a white colour due to condensation and freezing of the humidity present in the air.

The density of the liquefied gas is lower than that of water. LPG and LNG spilt on water floats on top of the water before evaporating. One litre of LNG gives off 600 litres of gas. One litre of LPG (butane) produces 235 litres of vapour. The liquid evaporates at its boiling point, which, for both LNG and LPG, is below 0^oC. Evaporating liquid cools the surroundings, causing cold burns to the skin and eyes and deforming some materials. Spilt liquified gas will evaporate quickly, and the gas formed is heavier than air. It will flow along the ground, enter cellars, drains and pits.

LPG and LNG contain impurities such as carbon dioxide and water vapour. Small amounts of methanol are added to dissolve the condensed humidity and prevent water vapours from forming solid ice, hydrating into the valves and regulators and by doing so blocking the flow of gas.

LNG and LPG are extremely flammable. Explosive concentrations in air are easily formed. The fire requires fuel, oxygen and an ignition source: below the lower explosive limit there is not enough fuel, and beyond the higher explosive limit the mixture is too poor in oxygen for combustion. The lower explosive limit for butane is 1.8% in air (by volume). The higher limit is 9.1 %. When the proportion of butane gas is within these limits, it can be exploded by any source of ignition such as a burning cigarette, a spark from switching on a light in the cellar, a spark from a metal tool or of any open flame. LPG gas/air mixture may travel along the ground to a distant ignition source.

At Port Hudson 60 tons of gas from a broken propane line escaped for 13 minutes to form a blanket 3-6 metres thick. This crept about 600 metres before being ignited at the refrigeration plant.

One litre of liquid butane forms 4660 litres of extremely flammable and possible explosive mixture with air.

The measured flame temperature of commercial grades of LNG and LPG is above 1900^oC.

The formulation of LPG may vary depending on the production line in refineries. Light fractions from distillation and cracking processes produce gases containing mainly propane and butane. LPG from secondary refinery processing may contain variable amounts of unsaturated hydrocarbons such as propylene, butylene and dienes, which can cause adverse health effects. LNG does not usually contain unsaturated hydrocarbon compounds and purification of natural gas leads to nearly pure product formulation of methane (98%).

LPG is unique among hydrocarbon fuels in its combination of properties and the hazards arriving from them. Rapid evaporation of a spill at low temperature to form a gas cloud, extremely flammability and density greater than air. Lighter hydrocarbon fuels disperse into the atmosphere; heavier hydrocarbons are liquids at normal conditions and evaporate at a slower rate. Following loss of containment, from a broken pipeline or damaged cylinder, LPG is emitted as a liquid under pressure, not as a liquid with gravity or gas under pressure. These properties are also the origin of the hazards related to handling of LPG.

Table 6. Main components of natural gases (LNG) from various sources (crude grade)

LNG flame and the exhaust gases, carbon dioxide and water vapour, are `clean' and specifically suited to processes where the flame and exhaust gases come into contact with production material. LNG is widely used in the glass and metallurgic industries.

Table 7. Properties of commercial LPG grades

Table 8. Properties of the main components in LNG and LPG

2. Effects

2.1. Physical and health hazards

LPG and LNG are extremely flammable, they are subject to local and international regulations and agreements when stored and transported. The storage installations and containers must be designed and build according to these regulations.

Electrostatic charges are formed when LPG and LNG flow in pipelines, during filtering, mixing, discharging and filling operations. These electrostatic charges have caused accidents when sparks formed ignite the extremely flammable liquid or vapour.

The low temperatures from evaporation of liquid produces cold burns. Storage containers may also become cold when liquid is drawn from them. The humidity in gloves, clothes and skin may freeze onto the contact point and stick to the cold surface. Do not force the frozen object apart but warm it gently, for example, with large amounts water, avoiding direct contact of water with liquefied gas.

The main components of LNG and LPG, methane, propane and butane, are not toxic. They are not irritant either to the eyes or the skin or by inhalation at low concentration. Repeated contact with liquefied gases causes skin irritations.

When mixed with air at very high concentrations LPG has anaesthetic effects, and by reducing the level of consciousness may lead to an accident. The narcotic effect of butane is greater than that of propane. Inhalation of increasing concentrations of LPG vapour causes weakness, headache, nausea, confusion, blurred vision and drowsiness. The vapour from the evaporating liquid act as a simple asphyxiant by decreasing the oxygen content specifically in confined spaces. These gases are odourless when pure and the odour threshold does not give warning of overexposure. Commercial gases contain added odorants to help to detect leakages.

At high concentrations these gases have shown in animal test to cause heart and cardiovascular adverse effects. These effects were reported to disappear after the exposure to the gases stopped.

Dienes may be present in LPG. 1,3-Butadiene has been classified as a probably carcinogen (IARC 1992).

2.2. Environmental effects

LPGs are low polluters and burn to produce non-toxic carbon dioxide and water.

Ground-water pollution is not likely as the liquefied gases are highly volatile. They will rapidly evaporate and disperse in the air. The main components of LPG undergo photochemical decomposition in the upper parts of the atmosphere. In LNG, methane is suggested to be one of the "greenhouse gases", as well as its combustion product, carbon dioxide. These gases have the effect of trapping the heat of the sun inside the atmosphere, thus raising the atmospheric temperature and may influence the climate of our planet.

3. Safety in handling LPG

LPG installations should have a systematic, planned approach as regards safety:

• regular inspections of the installation. In some countries safety and health plans must be submitted to and approved by the major hazard control authorities
• commissioning of loading/unloading procedures, maintenance work, etc.
• maintenance and examination
• fire precautions and emergency plan
• operational procedures in writing
• training of personnel

The flammability of LPG is the most important origin of accidents. Personnel handling these chemicals should be familiar with the hazards and they should be trained in safety procedures, equipment and personal protection. In case of a spillage, inhalation of the gases should be avoided using fresh air, positive pressure helmet or self-contained breathing apparatus. These are the only alternatives of personal protective equipment, as the gases cannot be filtered.

Contact with the cold, evaporating liquid should be prevented. The eyes should be protected whenever the danger of splashing is possible. Liquefied petroleum gases are good solvents of some materials, such as plastics and rubber, which should be considered when choosing protective clothing. Clothes which have been wetted by splashing should be removed without delay: the liquid gases may be trapped in the fibres and evaporate, resulting in a fire hazard when the person enters warmer area, e.g. comes into a warm room from outside.

Safety in the handling of gases provided in cylinders includes the following basic features:

• each cylinders should contain the identification markings explaining the specification to which it is made, the manufacturer, serial number, capacity to which it is designed (volume and weight when empty and equipped with valve and permanent fittings), last test date, test pressure, and the year of production.
• flexible tubes used in connecting the cylinder to the burning apparatus should be specifically manufactured for that purpose.
• connections should be gas-tight. This can easily be tested with soapy water, the escaping gas forms bubbles.
• the adjustments of the burner should be checked as incomplete burning releases toxic carbon monoxide gas.
• for high gas consumption the natural rate of evaporation does not produce enough gas for burning. The vapour pressure of the gas drops as the liquid gas cools. This becomes visible when the outer wall of the cylinder condenses frost from the air humidity at the level of the liquid level inside the cylinder. More than one cylinder should be installed in series to provide necessary gas flow. Under NO conditions should the frozen cylinder be warmed to overcome this effect.
• cylinders should not be kept inside a building unless connected to the burning apparatus or the storage specifications are fulfilled.
• cylinders should be kept in an upright position, fixed if necessary.
• nominally empty cylinders contain vapours of LPG; if the valve is left open air may enter the cylinder and mix with the vapour; a mixture within the explosive limits may ignite in filling operation; refillable cylinders should be treated in the same way as full ones whatever the state of their content.

4. Requirements in storage

The gases are compressed and stored under pressure. This reduces the size of containers as the liquid is more condensed. Their own pressure can be used in distribution on site and for mixing with air for combustion. No pumps, blowers, or induced draught are needed. This adds new dimensions to hazards and requirements for storage and transport, peculiar to LPG.

LPG and LNG are stored in cylinders and in fixed storage installations in fixed tanks.

In EU countries the liquefied gases are regarded as potential cause of major accidents when the quantity is large. EU Directive allows storage up to 50 000 kg in general storage facilities and to 200 000 kg in industrial specialized installation. Quantities above these limits are classified as major hazard installations and are subject of further legislation and regulations.

Storage facilities are subject to several legal requirements and registering concerning the location, technical design and fire safety of installation.

The storage area should be well ventilated; if outside, no other stacked material or vegetation should prevent the ventilation.

The regulations concerning distance limitations of other storage materials should be respected; compressed gases, flammable liquids, corrosive and oxidizing materials belong to these restricted substances.

All storage areas containing LPG must be clearly marked with warning notices forbidding smoking and open fire.

LPG should not be stored below ground level within a building or in a cellar. The storage areas should have no drain without a suitable cover or water seal to prevent the LPG vapour from entering the sewage system. There are also regulations concerning the distance of sewage openings from the stored LPG containers.

4.1. Fixed installations

LPG is stored in fixed tank containers to supply gas to a number of consumers. The consumers receive LPG vapour through general piping via a meter in the consumer's premises. This type of supply of LPG is commonly found in housing and industrial estates.

Storage tank location

Fixed tanks should be located in the open air. The vessels may be mounded or buried, but they may not be placed one above the other. Ventilation should be good, with screening bushes and other vegetation only on one side of the area. A minimum separation distance of 3 metres should be left between the LPG storage vessel and the top of the bunt of any tank containing flammable liquid, any hazardous substance or liquid oxygen.

The separation distance of the tanks from buildings, boundary property line or fixed source of ignition should be 2.5 metres for containers from 50 to 250 kg of LPG, 3 m for containers 250 to 1 100 kg LPG and 7.5 metres when the nominal container capacity is 1 100 to 4 000 kg LPG. The safety distance when using a fire wall is less, for example, for tanks with 250 to 1 100 kg LPG the distance of the tank should be not less than 1.5 metres from the fire wall.

The distance between the tanks in the group should be 1 metre. The group should not contain more than six tanks with a maximum capacity of 4 000 kg LPG, corresponding to a water capacity of 9 000 litres.

Design and materials

Fire walls are normally only on one side of a tank or a group of them. They can form part of the security fencing. The industrial type wire mesh should have height of at least 1.8 metres and leave a free space of 3 metres towards the tank containers. The fence should be secured to, for example, concrete poles; wood is not acceptable material. The base of the installation should be solid (concrete).

Piping should be properly constructed bearing in mind the low temperatures of the evaporating LPG. Steel piping is preferred. PE (polyethylene) piping may be used to convey LPG vapour. It should be protected against mechanical damage and ultraviolet light. Pressure regulation is needed with a high-pressure shut-off device when using PE piping. A second regulator with high and low pressure protection should be installed outside the user's building to protect the installation pipework and appliances.

Marking and identification of installation

The marking should be clear, indicate the contents of the tank and warn of hazards. Where pipelines are buried underground, markers should be installed at all road, rail, and river crossings.

Operations

When the LPG container is empty supplies are generally brought by road. The truck should be parked out of the main road in a position from which the driver can survey the loading equipment in its entire length. Overfilling of LPG tanks can have (and has had) extremely serious consequences.

The equipment and the pipelines should be regularly inspected (every 12 months) and records should be kept together with the construction drawings, calibration certificates of instruments and test results of the new installation prior the use.

An instruction and emergency manual should be given to the consumer explaining and giving instructions on how to carry out normal operations and maintenance activities. It should also include advice for abnormal situations and emergencies.

4.2. Cylinder storage area

The safe separation distances are subject to regulations for different quantities of LPG in cylinders. The sizes of the largest stacks on the storage area also affect the selection of the safety separation distances. A fixed ignition source could be, for example, a machine or a compressor with hot edges.

Table 9. LPG storage area of cylinders. Minimum safety separation distances from the nearest cylinder to boundary building or fixed ignition source (according to safety requirements for constructing of such an area).

Above 250 000 kilograms of stored LPG, the distance to the building from the nearest cylinder must be 20 metres; if the building has a fire wall towards the nearest cylinder, the distance of the stack from this fire-resistant, tested construction can be 7 metres.

A general recommendation for the size of cylinder stacks is 30 000 kg of LPG. Between the stacks must be gangways which are at least 1.5 metres for stacks not on pallets and 2.5 metres for palletized stacks. The vertical columns of stacks have a maximum height which is relative to the size of the used cylinder. However, columns of cylinders not on pallets should not exceed a height of 2.5 metres.

Table 10. The allowed heights (by weight) of different size of cylinders in vertical piles

5. Transport of liquefied petroleum gases

Specially designed tanks are needed for transporting LPG and LNG by rail and by road. The tanks are of cylindrical form with spherical bottoms. The pressure may be 20 000 kPa (100 kilopascal is equivalent to normal air pressure). Railroad tank capacity is in range to 130 m³ and road tanker to 40 m³. The technical requirements of these tanks include gauges, thermometers, two safety valves, indicator for maximum and minimum filling, device to check LPG level, devise to remove static electricity, baffles to reduce the hydraulic effects caused by sudden changes of vehicle speed and fire-fighting equipment.

You may calculate the volume of the gas cloud if 10 m³ of butane escapes from the tanker (1 litre liquid butane = 235 litres gas). You may also calculate the cloud volume of explosive mixture with air.

Transport by sea also uses tankers with heat-insulated reservoirs. The tank capacity of ships ranges upwards from 5000 m³. LNG needs to be carried in heat-insulated reservoirs, pressurized close to atmospheric pressure.

CHECKLIST

OPERATING PROCEDURE FOR UNLOADING LNG ROAD TANKER

1. The weight of the of the vehicle and its content is recorded at entrance

2. Permit and instructions to unload from the control room should be obtained

3. Unloading area checklist:

• Switch the engine and all electrical equipment off but leave the ignition key in place
• Chock the wheels
• Check the unloading permit
• Check availability of the fire-fighting equipment
• Check that the fire alarm and communication line are functioning
• Connect the grounding from receiving end to the tanker
• Check that hoses are of the right type
• Connect the flexible hoses from the fixed lines to the tanker
• Open the vapour return and liquid valves and replace the air from the connecting hose (with inert gas or LPG) before letting the LNG to the plant
• Read the tanker level gauge. When the tanker is nearly empty slow down the delivery flow
• Close the liquid delivery and vapour return valves when the minimum level in the tanker is reached
• Vent the connecting hose, warming the connections as required
• Disconnect the liquid hose and the vapour return hose
• Remove the grounding cable and the wheel chocks
• Return the equipment to its original place

4. The weight of the vehicle and the remaining content is recorded on leaving the premises

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