CONSEQUENCE ANALYSIS AND ENVIRONMENTAL CONSIDERATIONS
17.1 INTRODUCTION The three main potential hazards to consider for fertilizer solid raw materials and products in terms of damage to people, property and environment are – release of toxic fumes either due to fire and/or decomposition – explosion – spillage on land or in water.
17.2 TOXIC FUME HAZARD Most fertilizer materials thermally break down, when heated, releasing gases some of which may be toxic or harmful. Fertilizers based on ammonia tend to be more prone than others in this regard and they include, for example, ammonium nitrate and AN-based fertilizers, MAP, DAP and urea. They give off ammonia gas when decomposing. Those containing AN also release oxides of nitrogen. NPK fertilizers can give off a number of gases (e.g. ammonia, oxides of nitrogen and hydrogen chloride) depending on the source materials used. The nitrates of potassium, sodium and calcium are relatively more stable but when strongly heated can give off oxides of nitrogen. For the preparation of Safety Reports and emergency plans under Seveso regulations it may become necessary to do consequence analysis for certain accident scenarios such as a major fire with the evolution of toxic fumes. Such consequence analysis will involve the prediction of the concentration of toxic gases at various distances as the fumes disperse downwind in the atmosphere. Dispersion models are available from a number of organisations. Such models will require the ‘source’ term as an input, which is the rates of release of the toxic components. For straight AN the relevant information is available from a number of fire tests carried out by the UK’s Health & Safety Executive (Ref 52). Information about indicative compositions of the fumes released from AN-based NPK fertilizers is given in Section 6.1.9 and Ref 24. 65
17.3 EXPLOSION Most fertilizers are free from explosion hazards. Those fertilizers which can present explosion hazards (see Chapter 6) are required to pass the EC detonation test to prove they have high resistance to detonation and, therefore, the risk of a major explosion involving detonation of a significant amount of the stored fertilizer is extremely small. However, if for any reason a consequence analysis of a scenario involving a detonation in a stack or heap is required, the main point of consideration would be overpressures generated by the blast wave. Such over-pressures can be derived from an estimation of the TNT equivalent and the efficiency of explosion. Guidance on these aspects is available from papers published by TNO (Refs 53 and 54).
17.4 ENVIRONMENTAL HAZARDS Ammonium Nitrate Ammonium nitrate has low aquatic toxicity and does not present a major hazard to the environment if spilled on land. It is widely used as a fertilizer as it supplies nitrogen for plants. It is readily soluble in water and biodegradable; therefore, it is not persistent and does not bioaccummulate. The potential harm to the aquatic environment can be from: – toxicity of free (non-ionised) ammonia – oxygen depletion due to nitrification of ammonia/AN – eutrophication due to nitrate AN can create toxic effects when dissolved in water through the production of free (or non-ionised) ammonia. The extent of this reaction is very low below a pH of 7 and thus for most fertilizer products the toxic risk to the aquatic environment is negligible in practice. Nitrification of ammonia/ammonium ion to nitrate by bacterial action is a relatively slow process and therefore discharge into a running stream or tidal estuary waters is unlikely to result in harm. However, a high ammonium nitrate concentration in confined surface waters may induce the proliferation of algae (eutrophication) or, eventually, contamination of ground water by nitrates. Urea Urea has low aquatic toxicity and does not present a major hazard to the environment if spilled on land. Being a nutrient for plants it is widely used as a fertilizer. It is readily soluble in water and biodegradable; therefore, it is not persistent and does not bioaccummulate. Potassium nitrate Potassium nitrate will easily go into solution in the soil and dissociate completely into its ions. Both ions can participate in absorption and ion exchange processes. Under aerobic conditions the nitrate ion is chemically and biologically degradable. Like ammonium nitrate a high potassium nitrate concentration in confined surface waters may induce the proliferation of algae (eutrophication) or eventually, contamination of ground water by nitrates. Sodium nitrate Sodium nitrate will easily go into solution in the soil and dissociate completely into its ions. Both ions can participate in absorption and ion exchange processes. Under aerobic conditions the nitrate ion is chemically and biologically degradable. Like ammonium nitrate a high sodium nitrate concentration in confined surface waters may induce the proliferation of algae (eutrophication) or, eventually, contamination of ground water by nitrates.
Calcium nitrate fertilizer (CAS No. 15245-12-2) Calcium as an ion can participate in absorption and ion exchange processes. Under aerobic conditions the nitrate ion is chemically and biologically degradable. As with other nitrates, a high concentration in confined surface waters may induce the proliferation of algae (eutrophication) or, eventually, contamination of ground water by nitrates.
Monoammonium phosphate (MAP) Monoammonium phosphate may be harmful to aquatic life at relatively high concentrations; however, it has low acute toxicity to fish. Large-scale release may lead to the eutrophication of waterways. MAP easily dissolves forming the ions NH4 + and H2PO4 - . The ammonium is converted to nitrate whilst the latter is converted to PO4 3- and both are easily taken up by plants. Diammonium phosphate (DAP) Diammonium phosphate may be harmful to aquatic life at relatively high concentrations. However, it has low acute toxicity to fish. Large-scale release may lead to eutrophication of waterways. DAP easily dissolves forming the ions NH4 + and HPO4 2-. The ammonium is converted to nitrate whilst the latter is converted to PO4 3-; and both are easily taken up by plants. Superphosphates Superphosphates readily dissolve forming mono calcium phosphate. In calcareous, neutral or slightly acidic soil, it is quickly precipitated as available dicalcium phosphate, by calcium ions present in the soil solution. In acidic soil, phosphate is precipitated by iron and aluminium compounds
17.1 INTRODUCTION The three main potential hazards to consider for fertilizer solid raw materials and products in terms of damage to people, property and environment are – release of toxic fumes either due to fire and/or decomposition – explosion – spillage on land or in water.
17.2 TOXIC FUME HAZARD Most fertilizer materials thermally break down, when heated, releasing gases some of which may be toxic or harmful. Fertilizers based on ammonia tend to be more prone than others in this regard and they include, for example, ammonium nitrate and AN-based fertilizers, MAP, DAP and urea. They give off ammonia gas when decomposing. Those containing AN also release oxides of nitrogen. NPK fertilizers can give off a number of gases (e.g. ammonia, oxides of nitrogen and hydrogen chloride) depending on the source materials used. The nitrates of potassium, sodium and calcium are relatively more stable but when strongly heated can give off oxides of nitrogen. For the preparation of Safety Reports and emergency plans under Seveso regulations it may become necessary to do consequence analysis for certain accident scenarios such as a major fire with the evolution of toxic fumes. Such consequence analysis will involve the prediction of the concentration of toxic gases at various distances as the fumes disperse downwind in the atmosphere. Dispersion models are available from a number of organisations. Such models will require the ‘source’ term as an input, which is the rates of release of the toxic components. For straight AN the relevant information is available from a number of fire tests carried out by the UK’s Health & Safety Executive (Ref 52). Information about indicative compositions of the fumes released from AN-based NPK fertilizers is given in Section 6.1.9 and Ref 24. 65
17.3 EXPLOSION Most fertilizers are free from explosion hazards. Those fertilizers which can present explosion hazards (see Chapter 6) are required to pass the EC detonation test to prove they have high resistance to detonation and, therefore, the risk of a major explosion involving detonation of a significant amount of the stored fertilizer is extremely small. However, if for any reason a consequence analysis of a scenario involving a detonation in a stack or heap is required, the main point of consideration would be overpressures generated by the blast wave. Such over-pressures can be derived from an estimation of the TNT equivalent and the efficiency of explosion. Guidance on these aspects is available from papers published by TNO (Refs 53 and 54).
17.4 ENVIRONMENTAL HAZARDS Ammonium Nitrate Ammonium nitrate has low aquatic toxicity and does not present a major hazard to the environment if spilled on land. It is widely used as a fertilizer as it supplies nitrogen for plants. It is readily soluble in water and biodegradable; therefore, it is not persistent and does not bioaccummulate. The potential harm to the aquatic environment can be from: – toxicity of free (non-ionised) ammonia – oxygen depletion due to nitrification of ammonia/AN – eutrophication due to nitrate AN can create toxic effects when dissolved in water through the production of free (or non-ionised) ammonia. The extent of this reaction is very low below a pH of 7 and thus for most fertilizer products the toxic risk to the aquatic environment is negligible in practice. Nitrification of ammonia/ammonium ion to nitrate by bacterial action is a relatively slow process and therefore discharge into a running stream or tidal estuary waters is unlikely to result in harm. However, a high ammonium nitrate concentration in confined surface waters may induce the proliferation of algae (eutrophication) or, eventually, contamination of ground water by nitrates. Urea Urea has low aquatic toxicity and does not present a major hazard to the environment if spilled on land. Being a nutrient for plants it is widely used as a fertilizer. It is readily soluble in water and biodegradable; therefore, it is not persistent and does not bioaccummulate. Potassium nitrate Potassium nitrate will easily go into solution in the soil and dissociate completely into its ions. Both ions can participate in absorption and ion exchange processes. Under aerobic conditions the nitrate ion is chemically and biologically degradable. Like ammonium nitrate a high potassium nitrate concentration in confined surface waters may induce the proliferation of algae (eutrophication) or eventually, contamination of ground water by nitrates. Sodium nitrate Sodium nitrate will easily go into solution in the soil and dissociate completely into its ions. Both ions can participate in absorption and ion exchange processes. Under aerobic conditions the nitrate ion is chemically and biologically degradable. Like ammonium nitrate a high sodium nitrate concentration in confined surface waters may induce the proliferation of algae (eutrophication) or, eventually, contamination of ground water by nitrates.
Calcium nitrate fertilizer (CAS No. 15245-12-2) Calcium as an ion can participate in absorption and ion exchange processes. Under aerobic conditions the nitrate ion is chemically and biologically degradable. As with other nitrates, a high concentration in confined surface waters may induce the proliferation of algae (eutrophication) or, eventually, contamination of ground water by nitrates.
Monoammonium phosphate (MAP) Monoammonium phosphate may be harmful to aquatic life at relatively high concentrations; however, it has low acute toxicity to fish. Large-scale release may lead to the eutrophication of waterways. MAP easily dissolves forming the ions NH4 + and H2PO4 - . The ammonium is converted to nitrate whilst the latter is converted to PO4 3- and both are easily taken up by plants. Diammonium phosphate (DAP) Diammonium phosphate may be harmful to aquatic life at relatively high concentrations. However, it has low acute toxicity to fish. Large-scale release may lead to eutrophication of waterways. DAP easily dissolves forming the ions NH4 + and HPO4 2-. The ammonium is converted to nitrate whilst the latter is converted to PO4 3-; and both are easily taken up by plants. Superphosphates Superphosphates readily dissolve forming mono calcium phosphate. In calcareous, neutral or slightly acidic soil, it is quickly precipitated as available dicalcium phosphate, by calcium ions present in the soil solution. In acidic soil, phosphate is precipitated by iron and aluminium compounds