Risk analysis and handling of ammonia leaks

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Risk Analysis and Handling of Ammonia Leaks I. Introduction In recent years, ammonia leak accidents have occurred from time to time in China. According to statistics, 17 ammonia leak accidents have taken place in a city in Jiangsu Province over the past 5 years, resulting in 1 death and 8 injuries. On July 6, 2005, a liquid ammonia leak occurred in a town in Nanhu District, Shanghai; hundreds of households in the surrounding area were affected by ammonia fumes, and over a hundred people were poisoned and taken to hospitals for treatment. The hazards of ammonia leaks cause severe damage to ** and people’s lives and property, drawing widespread attention from the entire society. Therefore, dealing with ammonia leaks is a very important and challenging task for fire departments. II. Hazards of ammonia leaks Ammonia, also known as liquid ammonia, is a toxic and flammable gas. It is an important chemical raw material, produced by the direct combination of hydrogen and nitrogen under high temperature, high pressure, and in the presence of catalysts. Ammonia has a wide range of uses; it can be used to produce ammonium salts, *ao acids, and urea, as well as serving as a refrigerant in refrigerated warehouses. Ammonia is soluble in water, forming an alkaline solution of ammonium hydroxide. Its solubility in water at 20°C is 34%, meaning that 1 part of water can dissolve 700 parts of liquid ammonia. The aqueous solution of ammonia is called ammonia water. For the convenience of transportation and storage, gaseous ammonia is usually converted into liquid ammonia through compression or cooling. In cases of leaks during production, storage, transportation, or use, it can easily lead to fires, explosions, or poisoning incidents; improper handling can result in serious consequences. 　　(1) Easy vaporization and diffusion Ammonia (NH3) is a colorless gas with an irritating odor; its molecular weight is 17.03, its gas density is 0.59, and its liquid density is 0.82. Its diffusion coefficient is 0.198, and its boiling point is -33.5°C. At room temperature, ammonia exists in gaseous form; it turns into a liquid state when subjected to a pressure of 1.554 MPa at room temperature or when cooled to -33.4°C. Liquid ammonia is stored under high pressure or low temperatures. In the event of a leak, it transitions from the liquid phase to the gas phase, vaporizing rapidly and causing its volume to increase significantly. The ammonia that does not vaporize promptly becomes aerosolized in the form of droplets within the vapor ； In the early stages of a leak, due to the partial evaporation of liquid ammonia, the density of the ammonia vapor clouds is higher than that of the air. The ammonia vapor drifts with the wind, leading to the formation of large areas contaminated by toxic substances as well as areas prone to combustion and explosion. It is necessary to evacuate people within the affected area promptly and take measures to prevent the occurrence of fires. On July 8, 2002, while a storage tank capable of holding 20 cubic meters of liquid ammonia at a fertilizer factory in Shandong was filling a liquid ammonia tanker, the metal hose on the tanker burst, causing the liquid ammonia to spread rapidly. Within just a few minutes, ammonia gas covered the entire factory area, threatening the lives of 2,000 people. As a result of this accident, 105 people were poisoned, 13 died, 24 were seriously injured, and 12 suffered moderate injuries. 　　(II) Prone to poisoning and injuries Ammonia is a toxic, irritating gas with a foul odor; it is volatile. When ammonia leaks into the atmosphere and spreads over a certain area, it can cause acute poisoning and burns. The maximum allowable concentration in the air is 30 mg/m3. When the ammonia level in the air reaches 0.5–0.6%, it can cause poisoning in people within 30 minutes ； The main routes through which ammonia enters the human body are the skin, respiratory tract, airways, and digestive tract. Symptoms of mild poisoning include a dry and burning sensation in the eyes and mouth, tearing, runny nose, coughing, hoarseness, difficulty swallowing food and drink, as well as dizziness and headache. Upon examination, congestion and swelling of the conjunctiva can be observed, and a few dry rales can be heard in the lungs ； Symptoms of severe poisoning include severe second-degree chemical burns to the skin of exposed areas such as the head and face due to high concentrations of ammonia; coma, mental confusion, and spasms may also occur. Myocarditis or heart failure can be caused as well. In a few cases, death occurs as a result of reflexive laryngeal spasm or respiratory arrest. 　　(III) Flammability and explosiveness 　Ammonia is both a toxic gas and a flammable gas. Its auto-ignition temperature is 651°C, with a calorific value of 2.37–2.51 J/m3. The critical temperature is 132.5°C, and the critical pressure is 11.4 Mpa. When its concentration in air reaches 11–14%, it can catch fire upon exposure to an open flame; the flame appears yellow-green. The presence of oils increases the risk of combustion even further ； When the ammonia concentration in the air reaches 15.7%-27.4%, it can explode upon contact with a fire source; the concentration at which ignition is most likely to occur is 17%, resulting in a maximum explosion pressure of 0.58 Mpa ； When a liquid ammonia container is heated, it expands and the pressure increases, which can cause the cylinder or tank to explode. 　　(IV) Environmental pollution risk 　Ammonia can pollute the air; driven by wind, this toxic gas spreads through the air, causing widespread air pollution that poses a threat to both humans and animals. If large amounts of liquid ammonia leak into water bodies such as rivers, lakes, and reservoirs, it causes water pollution; in severe cases, the water in those areas cannot be used without treatment. On June 28, 2005, a leak of liquid ammonia occurred in the pyrolysis tank area of a chemical plant in Nanjing, killing virtually all the vegetables, crops, and trees within a two-kilometer radius, as well as many frogs in the water. 　　(5) Prone to secondary accidents Ammonia is unstable and decomposes when exposed to heat; it reacts violently with elements such as fluorine and chlorine. If exposed to high temperatures, the pressure inside the container increases, posing a risk of cracking and explosion. 　　(VI) High difficulty in handling Ammonia is stored in containers in liquid form by pressurizing or cooling it from a gaseous state. Due to variations in the methods of storing liquid ammonia, the pressure within the containers, the location of leaks, and the size of cracks, implementing measures such as sealing leaks or transferring the substance requires high technical skills, making handling it quite difficult. 　　III. Response measures taken by the fire department during ammonia leaks (1) Response to alarms Upon receiving an alarm, it is necessary to ascertain the time of the incident, the exact address, the medium in which the substance is contained, whether there have been any fires or explosions, and if there are any casualties. When mobilizing resources, efforts should be made to use as few assets as possible while still meeting the on-site needs; specialized equipment such as chemical defense vehicles and emergency rescue vehicles must be deployed promptly, and departments such as the police and medical rescue services should be called upon to assist with the rescue efforts. 　　(II) Personal protection Personnel entering the site or the restricted area must wear isolated breathing apparatus and fully enclosed fire and chemical protective suits to prevent ammonia from entering the body ； Those entering low-temperature leak sites must wear cold-protective clothing, and should strive to enter and exit quickly to minimize time spent there and prevent frostbite. 　　(III) On-site inquiry Upon arriving at the scene, firefighters should ask in detail whether there are any people trapped ； The location of the leak, whether it is a liquid-phase or gas-phase leak, and the amount of leakage ； Have any measures been taken to stop the leaks? Are there any equipment for sealing leaks? Is it possible to carry out actions such as sealing leaks or transferring liquids to another container? ； In the case of a tank farm, it is necessary to determine the overall layout, the capacity of the tank that is leaking, the actual storage volume, the storage volume of adjacent tanks, as well as the total storage capacity. 　　(IV) Reconnaissance and detection: Determine the area where the leakage has spread and check for any sources of fire in the surrounding area ； Use instruments to detect gas concentrations and diffusion ranges at the accident site ； Measure the wind speed and direction at the site and in the surrounding area ； Search for those in distress and trapped, and promptly organize rescue and evacuation efforts ； Determine the attack route and positions. 　　(5) Establishing a security perimeter 　Based on the information gathered and the results of investigations, the scope of the security perimeter is determined; security signs are installed, and security personnel are deployed to strictly control the entry and exit of people and vehicles. Throughout the entire handling process, continuous monitoring is carried out, and the scope of the security perimeter is adjusted as needed based on the findings of this monitoring. 　　(VI) Evacuation and rescue: Evacuate all unauthorized personnel from the area where the leak has occurred and from any areas that may be affected by its spread ； Form a rescue team, carry rescue equipment, and rush into the dangerous area to use the appropriate rescue methods and bring all those in danger to a safe location ； Register the rescuers and provide first aid at the scene ； Those with more severe injuries are sent to medical emergency services for treatment. 　　(7) Eliminating hazards 　　1. Prohibit the use of open flames. Depending on the situation, cut off all power supplies within the secure area, extinguish open flames, and stop the operation of high-heat equipment ； 　　2. Dilution to reduce toxicity. Centered on the leak point, a water curtain or spray nozzles should be installed around the tank or container to emit misty water for dilution and toxin reduction; however, direct water flow should not be used. Prevent leaks from entering water bodies, sewers, basements, or enclosed spaces. 　　3. Disperse gases. The leaked ammonia will form vapor clouds that spread above buildings indoors; it is necessary to deploy a certain number of spray nozzles to spray water onto the ground and into the air, in order to change the direction and altitude of the ammonia vapor dispersion. Mobile exhaust fans can also be used to supply air to support the rescue efforts ； Natural ventilation and mechanical exhaust systems should also be enhanced indoors to disperse and dilute the floating air masses ； Do not use a straight-flow water gun to spray at the leaked liquid ammonia or the source of the leak in order to disperse and dilute it ； If steam pipeline facilities are available, a steam pipe can be connected to release steam in order to dilute the leaked gas. 　　4. Close the valve to cut off the source. In the event of an ammonia leak from a production facility, the engineering technicians of the unit involved in the incident or those who are familiar with the situation should be responsible for closing the valves on the pipes that transport the material, thereby cutting off the source of the leak. Firefighters shall be tasked with using water guns to provide coverage and assist with these operations. 　　5. Transfer by pouring. When a storage tank or container leaks and the leak cannot be sealed, the liquid ammonia can be diverted into other containers or tanks using a diversion method. 　　6. Soaking and hydrolysis. During transportation, if the valve of a small-sized liquid ammonia cylinder is damaged and leakage occurs, and there are no tools available to stop the leak, the cylinder can be immersed in a dilute acid solution for neutralization; it can also be submerged in water, but care must be taken to prevent it from entering other rivers and causing water pollution. 　　7. Chemical neutralization. In the event of a minor leak in the wall of a storage tank or container, chemical neutralization can be used; this involves adding acidic substances to the water tank of a fire truck and spraying them onto the tank or container in order to reduce the damage ； The leaked liquid ammonia can also be directed into an acidic solution to be neutralized, resulting in harmless or slightly toxic wastewater. 　　8. Transfer the chemicals that react with it. For chemical substances such as fluorine and chlorine present at the accident site that can undergo violent chemical reactions with ammonia, those that can be moved should be moved immediately, while those that cannot be moved must have protective measures taken to prevent explosions. 　　9. Plugging leaks in appliances. If there is a leak in the pipe wall, and the leak occurs before the valve or the valve is damaged and cannot be used to stop the leak, various types of sealing gaskets, sealing wedges, sealing bags, and other tools can be employed to seal the leak. Micro-porous leaks can be sealed by screwing screws with adhesive into the holes ； If a leak occurs due to a tear in the tank wall, specialized devices such as inflation bags or inflation pads can be used to seal the leak from the outside ； For leaks in pressurized pipes, **type inflation-based sealing strips or specialized tools such as those with metal housings lined with rubber gaskets can be used to seal the leaks from both the inside and outside ； If the valve flange or gasket is damaged and leakage occurs, it can be sealed using different types of flange clamps along with the injection of sealant ； Special valve sealing tools (sets) can also be used directly for sealing leaks ； 　　10. Transfer. When a storage tank or container leaks and the leak cannot be sealed, diversion and transfer methods can be used to eliminate the hazard. In the tank area, tank transfer should be carried out as early as possible if the conditions permit. In the event of a leak from mobile tank trucks or similar, it can be transferred to a location where tank dumping is possible, if conditions permit. Pouring and transferring must be carried out under the cover of a spray water gun to ensure safety. 　　(8) On-site first aid: The rescued victims who have been poisoned should be decontaminated immediately and then handed over to medical rescue teams for on-site first aid. After preliminary treatment, they should be rushed to a hospital for further treatment. 　　(IX) Decontamination 1. Site decontamination Depending on the physical and chemical properties of liquid ammonia and the specific extent of contamination, different decontamination methods can be employed: chemical disinfection. That is, acidic solutions such as dilute salts are sprayed on the contaminated area or the surface of the affected objects, where a chemical reaction takes place that alters the properties of the toxins, turning them into non-toxic or less toxic substances ； Physical disinfection method. That is, using substances with adsorption capabilities such as adsorption pads and activated carbon to carry out adsorption, recovery, transfer, and treatment ； Polluted air can be dispersed and its toxicity reduced using a water-driven exhaust fan ； The polluted area can also be temporarily sealed off, relying on natural factors such as sunlight, rain, and ventilation to eliminate the toxic gases ； Mist water can also be sprayed to dilute and reduce toxicity. 　　2. Equipment decontamination All vehicles and equipment that enter the contaminated area must be decontaminated. 　　3. Personnel Decontamination 　Decontamination stations should be set up at the boundary between the hazardous area and the safe area. All personnel entering the hazardous area must be decontaminated. In case of skin contact, remove the contaminated clothing immediately and rinse thoroughly with 2% boric acid solution or plenty of clean water. In case of eye contact, lift the eyelids immediately and rinse thoroughly with plenty of flowing water or saline for 15 minutes. 　　(10) Clearance and handover 　　Count personnel, vehicles, and equipment ； Remove the security measures, ensure proper handover, and evacuate safely. 　　IV. Precautions for fire departments during the handling of ammonia leaks 　　(A) Selection of combat positions 　　The location of the command post and the parking area for firefighting vehicles should be at an appropriate distance from the area where the ammonia is leaking; they should be positioned in a location upwind. The front of the fire trucks should face away from the source of the leak, so that they can evacuate safely and quickly in case of any emergencies ； Where possible, water sources located in the upwind direction should be utilized. If, due to site conditions, it is necessary to use fire-fighting water sources in the downwind direction, then appropriate personal protective measures must be provided for the drivers and those responsible for supplying water ； The attack route should be chosen upwind or at an oblique angle upwind of the spill area, and water gun positions as well as a command post should be established. During the cleanup of the spill, water gun operators should use mist or scattered water jets for dilution. 　　(II) Prohibition of all sources of fire All sources of fire are prohibited within the exclusion zone. All persons entering this zone are not allowed to wear synthetic clothing or shoes with metal studs, and they are not permitted to bring metal tools into the affected area to carry out rescue operations. At the same time, mobile communication devices such as BB phones, cell phones, and ordinary radios must be turned off, and all power supplies within the security zone must be cut off. 　　(III) Evacuate unrelated personnel 　　Promptly evacuate all unrelated persons from the site of the leak and any areas that may be affected by its spread. Evacuation should be carried out by local authorities, public security forces, and firefighters, and it must proceed in an orderly manner. At the same time, attention must be paid to the safety of the people during evacuation; the evacuation order should be such that those in the area where the leakage occurs or in areas with a high level of danger are evacuated first, followed by those in areas that may be affected by the danger ； First, those with limited mobility such as the elderly, weak, sick, disabled, women, and children, and then those with better mobility ； Lower windward personnel first, then upper windward personnel. The evacuation location should be upwind of the spill site, and the evacuation distance should be determined based on the level of danger at the accident site. 　　(IV) Control of personnel involved in the operations 　　Those who enter the ammonia leak area to carry out emergency response tasks must be strictly controlled; the selected personnel should be professional and highly skilled, and they need to wear adequate personal protective equipment. Water guns that can spray water in a wide range should be used for protection. Those entering and leaving the leak area must have their entry and exit times recorded. Personnel other than those involved in the emergency response are not allowed to enter. For those who need to stay in the area for an extended period, rotations should be implemented. 　　(5) Appoint safety monitors Safety monitors should be assigned to oversee all areas at the disaster relief site throughout the entire process. They need to remain highly vigilant and constantly monitor for any potential dangers that may arise during the rescue operations, detecting early signs of such threats. The personnel involved in the rescue efforts must stay alert and sensitive, and all actions taken must ensure that fires, explosions, poisoning, frostbite, or other injuries do not occur. In case of an emergency that threatens the lives of those involved, the commander should promptly order a retreat. 　　(VI) First aid for poisoned persons: Those who are slightly poisoned at the scene should be immediately moved to a place with fresh air. The skin and face that have come into contact with the poison can be washed with water. At the same time, it is important to monitor the health status of those involved in dealing with the ammonia leak and to conduct health checks; those with severe symptoms should be taken to the hospital for treatment immediately. 　　(7) Operations that involve technical difficulties should be carried out by the unit’s technical personnel. Some ammonia production and storage facilities operate under low temperatures or high pressures, making them complex to manage and highly dangerous. Transferring liquid from one container to another must be done by technical personnel who are familiar with the equipment, the manufacturing process, and have extensive operational experience. Rescue personnel from public security fire departments should act under the guidance and coordination of these technical personnel; they must avoid acting hastily or recklessly. 　　V. Conclusion Although ammonia is a toxic and flammable gas that spreads everywhere in the event of a leak, contaminating the environment and causing poisoning or fire and explosion accidents, proper handling procedures can minimize such incidents when they do occur.