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Safety Measures for Hydrocyanic Acid Raw Material Chemical Production Plant

Date: Oct 14, 2022

    Hydrocyanic acid often used as a kind of raw material in chemical production. Since hydrocyanic acid is both highly toxic and has the risk of fire and explosion, for chemical production enterprises that use hydrocyanic acid as raw materials, in order to prevent the occurrence of acute poisoning accidents and fire explosions of hydrocyanic acid, it is very important and necessary to formulate corresponding security measures.

1. Characteristics of Hydrocyanic Acid

    Hydrocyanic acid is a colorless and transparent liquid, volatile, white poly, and has a bitter almond taste. The flash point of hydrocyanic acid is 17.8 ℃, which belongs to the Class A fire hazard substance, the explosion limit is 5.6%~40% (volume fraction), the relative molecular mass is 27.03, the hazard category is the 6.1st category of toxic substances, and the liquid relative density is 0.697 ( 18°C), the gaseous relative density is 0.93 (air=1). When acute poisoning occurs at high concentrations in the air, the patient will lose consciousness almost immediately, develop respiratory paralysis, followed by cardiac paralysis.

2. Anti-virus security measures

    2.1 Antivirus measures in the production process

    (1), Regularly monitor the air in the production workshop

    (2), The monitoring and testing of the airtightness of production equipment (or facilities) containing hydrocyanic acid should be strengthened. Maintenance workers must wear protective equipment when overhauling; on-site personal washing facilities and eyewashes should be provided.

    (3), Once the occurrence of operators hydrocyanic acid and other acute poisoning accidents in the process of production, it should be ensured that effective rescue and treatment measures can be taken in time, monitoring and protection should be strengthened, especially when the air pressure is low.

    (4), In places where oxycyanic acid liquid may leak, impermeable building materials should pave the ground and set up a cofferdam.

    (5), New fillers and gaskets with high temperature resistance, corrosion resistance and wear resistance should be used to improve the tightness of reaction equipment, valves (sampling valve, pouring valve, etc.), pipeline flange connection and airflow sealing to prevent the diffusion and leakage of harmful substances.

    (6),If the hydrocyanic acid solution is accidentally splashed on clothes or skin, immediately take off the contaminated clothes, rinse with plenty of water.In serious cases, it needs to be washed with 0.5% sodium thiosulfate solution or soaked in sodium thiosulfate solution to detoxify.

    (7), The sampling of the materials in the process device should adopt a closed circulation system; the liquid level indication of the materials should not use a glass tube liquid level gauge; the sampling point of hydrogen cyanide should be located in a place that is easy to sample and can be quickly evacuated. The sampling valve should be kept in an iron box with double locks, and two people will unlock and take samples at the same time. The sampling personnel should wear compressed air respirators and airtight protective clothing.

    (8), Exhaust gas containing hydrocyanic acid can be incinerated by torch. Since the exhaust gas contains hydrocyanic acid and has self-polymerization, it shall not be discharged into the public torch pipe network in the plant area, and a dedicated torch can be set up. The torch should be equipped with a permanent light and a TV monitoring system.

    (9), Waste water and waste containing hydrocyanic acid need to be incinerated by incinerator; the incinerator should use a constant burner and set up a TV monitoring system.

    (10), The vaporizer of hydrocyanic acid shall not be arranged in the torch area or incinerator area.

    (11), If the lips are splashed with hydrocyanic acid solution, they should be washed with sodium thiosulfate solution immediately and rinsed to detoxify; it is strictly forbidden for operators to eat or drink in the workplace.

    2.2 Industrial Hygiene Auxiliary Facilities

    (1), The hygienic characteristics of the process equipment using hydrocyanic acid as the material belong to Class 1, and production sanitation rooms (washrooms, laundry rooms), living rooms (restrooms, toilets)and dressing roomshould be set up. Casual clothes and work clothes should be stored in separate rooms. The dressing room should be well ventilated, and its construction area should be designed according to 1.5m2 per employee.

    (2), Due tothe hydrocyanic acid leakage accident may also occur chemical burns and skin absorption caused by acute poisoning, so the accident shower, eye washer and changing room should be set up, and set up 24 hours of continuous water water supply equipment to meet therequirement of production and operation.

3, Fire and explosion-proof safety measures

    3.1 Fire and explosion protection in the process

    (1), In order to prevent the self-polymerization of hydrocyanic acid, the liquid hydrocyanic acid pipeline of the input device should be accompanied by frozen salt water to maintain low temperature transportation.

    (2), Measures should be taken to ensure that the amount of hydrocyanic acid added does not exceed the specified standard

    (3), The pump room for transporting hydrocyanic acid should be set apart from other pump rooms; the pump for transporting hydrocyanic acid should use a shield pump or a magnetic pump to prevent the leakage of hydrocyanic acid from the dynamic seal of the pump.

    (4), Storage tanks for hydrocyanic acid should not be installed in the device area.

    (5), In order to prevent the hydrogen cyanide polymer from sticking to the pipeline and valve seat, the inlet of the safety valve should be connected with nitrogen blowing.

    (6), The air tightness of the reaction system should be ensured during the structural design, sealing form and equipment installation process of the reaction kettle, and leakage should be strictly prevented.

    (7), All metal pipes should be welded except for flange connection.

    (8), A block valve and a figure-8 blind plate should be installed at the boundary of the device, a platform should be installed at the block valve, and a platform with a length equal to or greater than 8m should be equipped with steps in two directions.

    (9), In order to prevent leakage and leakage of the hydrocyanic acid pipeline, the thickness of the pipe wall should be tested regularly, and the weld seam should be inspected with a non-destructive flaw detector.

    (10), The hydrocyanic acid pipeline should have a slope, and should not be banded. Valves should be used sparingly to avoid dead ends, so as to avoid poisoning accidents during shutdown and maintenance.

    (11), The underground cable trench of the power distribution cabinet in the installation area should have measures to prevent the accumulation of combustible gas or the entry of sewage containing combustible liquid. The trench can be filled with sand when the cable is laid, and drainage facilities should be set up; where the cable communicates into the power distribution room and the operation room, it should be filled and sealed with flame-retardant materials.

    (12), The cables should be of flame-retardant type. The cables leading to the junction box (port) of the electrical equipment should wear explosion-proof flexible connecting pipes, and the lines laid on the frame should be laid through galvanized steel pipes.

    (13),The electrical lines in the installation area should be laid in accordance with the technical requirements of steel pipe wiring, and must be isolated and sealed.

    (14), For other electrical equipmentbut the lighting fixtures, a special grounding wire should be used. The lighting fixtures can use the metal pipeline system with reliable electrical connection as grounding wire, but pipelines for transporting flammable substances shall not be used.

    (15), The division map of the explosion hazard area in the installation area should be drawn as required. All electrical equipment and lighting fixtures in the explosion-hazardous area shall be of suitable explosion-proof type, and the grade and group of the explosion-proof electrical equipment selected shall not be lower than ⅡBT1.

    3.2 Alarm device

    (1), The process unit area, control room, and analysis room should be equipped with a hydrogen cyanide detection and alarm device; the patrolling inspectors should be equipped with a portable hydrogen cyanide detection and alarm device.

    (2), If there are other Class A media (non-hydrocyanic acid toxic gas) in the production site, a flammable gas alarm should be set at the same time.

    (3), The alarm device should be arranged on the windward side of the wind direction of the minimum frequency of the release source, and the radius of the horizontal plane covered should be 7.5m indoors and 15m outdoors.

    (4), The alarm instrument should be a relatively independent instrument system; the hydrocyanic acid alarm instrument can be selected from gel electrolysis (battery type) type, diaphragm electrode type or constant potential electrolysis type, and should be powered by an uninterruptible power supply (UPS).

    3.3 Automation Control

    (1), For the production process that may escape hydrogen cyanide gas, automatic operation should be adopted as much as possible, and reliable exhaust and purification and recovery devices should be designed to ensure that the operating environment and the concentration of harmful substances discharged meet relevant standards.

    (2), Equipment and pipelines should be equipped with corresponding instruments, alarm signals, automatic interlock protection or emergency shutdown facilities according to the fire hazard and operating conditions of the materials in them.

    3.4 Buildings

    (1), The structures in the installation area shall be designed according to the fire resistance level of Class II or above.

    (2), The load-bearing steel frame, bracket, skirt and pipe frame of the structures in the installation area shall be covered with a refractory layer, and the fire resistance rating shall not be less than 1.5h.

    (3), The refractory layer of the beams and columns of the main strip at the bottom of the steel pipe frame of hydrocyanic acid should not be lower than 4.5m; all the beams, columns and diagonal supports should be covered with the refractory layer.

    3.5 Lightning protection

    (1), The lightning protection of the device should be fortified according to the second type of buildings.

    (2), The main metal objects such as equipment, pipelines, and steel frames in the installation area should be connected to the direct lightning protection grounding device or the protective grounding device of electrical equipment.

    3.6 Anti-static

    (1), A special connection terminal should be set at a certain position of the equipment and pipeline as the connection point of electrostatic grounding. The grounding branch and connecting wires should be multi-strand metal wires or metal conductors with sufficient mechanical strength, corrosion resistance and not easy to break.

    (2), Process pipe racks (or pipes) and equipment and containers that may generate static electricity should be reliably grounded, and the grounding resistance of each group of specially designed electrostatic grounding bodies should be less than 100Ω. All metal parts of the pipeline system in the installation area, including the metal cladding layer of the sheath, must be grounded; both ends of the pipeline, as well as branches and turns, should be grounded with an anti-static and anti-induced lightning.

    (3), The working neutral line of the lighting circuit, the working neutral line of the three-phase four-wire system, and the dedicated grounding trunk line of the DC circuit shall not be used for electrostatic grounding.

    (4), The material conveying pipeline can be used as the air-termination device itself, and the connection between the flange and the valve should be equipped with a metal jumper. When the flange is connected with more than 5 bolts, the flange may not be bridged by metal wires, but it must form an electrical path.

    3.7 Other requirements

    (1), Containers and pipelines such as reactors in the process unit should be equipped with nitrogen replacement facilities.

    (2), The air tightness test of the reaction system before feeding the device should be strictly checked. There should be no leakage in the equipment and pipelines involving hydrocyanic acid.

    (3), Hydrocyanic acid is very corrosive to metals. For the gaskets of process equipment, pipes, flanges and valves, corrosion-resistant materials should be selected to prevent leakage due to corrosion, causing poisoning and fire accidents. 

    (4), If a TV monitoring system is installed in the installation area, the camera in the explosion-proof area should be an explosion-proof type, and the monitoring screen can be installed in the control room outside the explosion-proof area.

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