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I. Basic Measures to Improve Explosion Protection Safety in Electrical Installation for Pharmaceutical Workshops
1. Overview
In pharmaceutical synthesis and extraction workshops, due to the extensive use of volatile organic substances, the vapors of these substances mix with air in certain proportions, reaching explosive concentrations. Upon encountering open flames, high temperatures, electric arcs, etc., combustion or explosion can occur. These workshops naturally become flammable and explosive hazardous areas. Therefore, explosion protection safety must be seriously considered as the primary factor in electrical design.
2. Basic Measures to Improve Electrical Explosion Protection Safety
Correct Selection and Standardized Installation of Wires, Cables, and Electrical Equipment
The national standard GB50058-92 "Code for Design of Electrical Installations in Explosive Atmospheres and Hazardous Areas" indicates that in explosive gas atmosphere Zones 1 and 2:
The rated voltage of insulated wires and cables used for low-voltage power and lighting circuits must be not lower than the working voltage and should not be less than 500V.
The minimum cross-section for copper-core cables in Zone 1 is 2.5 mm²; whereas in Zone 2, the minimum cross-section for copper-core cables is 1.5 mm².
Luminaires, switches, motors, and their control buttons should be selected as explosion-proof types, and the explosion-proof level should be higher than the level and group of the flammable and explosive substances.
For example: The flammable and explosive substances in extraction workshops are mostly ethanol, and the classification level and group for ethanol is IIAT2. Therefore, we should select equipment with an explosion-proof level of dIIBT3 or higher. Wiring for luminaires should be laid in galvanized steel conduits and adopt a three-wire system, i.e., adding an extra grounding protection PE wire. The cross-section of this PE wire should be the same as the phase wire's cross-section, and it should be reliably electrically connected to the luminaire's casing. The galvanized steel conduit should also be reliably grounded.
Power distribution line design should primarily use cable trays. The selected cables should be flame-retardant power cables with a withstand voltage of 1000V.
Cables should be run along walls or columns near equipment, routed through conduits down to buried underground, laid to the motor side, and then connected to the motor terminal inlet using explosion-proof flexible conduits.
Openings in cable trays or galvanized steel conduits passing through walls or floors between different zones should be tightly sealed with non-combustible materials to prevent explosive mixtures from diffusing through electrical conduits from hazardous areas to non-hazardous areas. Sealing points should preferably be located on the low-hazard area side of the partition wall between high-hazard and low-hazard areas. Cables in Zones 1 and 2 must not have intermediate joints.
Additionally, it is best not to use mobile or portable equipment within explosion-proof workshops. Collisions, friction between metal casings, or accidentally dropping them onto concrete floors can potentially generate electrical sparks, making them ignition sources.
Static Electricity Grounding
Static sparks can easily ignite explosive mixtures. Therefore, static electricity grounding plays an important role in explosion protection.
The static electricity grounding main should preferably be set as a closed ring throughout the explosion-protected area. When exposed, use 25×4 galvanized flat steel, installed along the perimeter walls at a height of 0.3m from the ground. When concealed, use 40×4 galvanized flat steel, laid under the screed. Whether exposed or concealed, it should connect to the main equipotential bonding terminal board at at least two points. Grounding branches use 12×4 or 25×4 galvanized flat steel, and should be reliably electrically connected to process equipment and pipelines, HVAC ducts, metal containers, normally unenergized metal enclosures of electrical equipment, etc. Connection points should be treated for corrosion protection.
The resistance value of the static electricity grounding system should not exceed 1 MΩ. The ground resistance value of a specifically installed static electricity grounding electrode should not exceed 100Ω. In practical design, natural grounding electrodes or grounding electrodes for other purposes should be fully utilized as the grounding body for the static electricity grounding system (excluding independent lightning protection grounding devices). When the grounding system uses a combined grounding electrode method, the grounding resistance value should be ≤1Ω.
Lightning Protection Grounding
Buildings with explosive hazard environments should be classified as Class I or Class II lightning protection based on the nature of the flammable and explosive substances, and corresponding measures against direct lightning strikes and lightning induction should be taken. Specific methods for lightning protection and grounding can be referred to in the relevant design codes and standard detail drawings, and will not be elaborated here. Only reasonable lightning protection and grounding measures designed effectively can reduce lightning disaster, thereby lowering the probability of explosion risk.
Installation of Combustible Gas Detection and Alarm Instruments
When abnormalities occur in a certain part of the process flow, flammable and explosive substances might be released at pumps, pipe valves, flanges, etc. These substances cannot be detected by human senses alone. Only by installing combustible gas detectors can the concentration of on-site explosive mixtures be monitored intuitively, allowing for timely and effective preventive measures to reduce the mixture concentration and explosion risk.
When detecting combustible gases heavier than air, the detector's installation height should be 0.3-0.6m from the ground. If too low, indoor water splashing or outdoor rain splash can damage the detector and reduce sensitivity; if too high, it exceeds the height where heavier-than-air gases tend to accumulate, possibly failing to detect the gas.
When detecting combustible gases lighter than air, the detector should be installed 0.5-2m above the release source, and the horizontal distance from the release source should preferably be no more than 5m. This allows rapid detection of combustible gas, reducing the time from leak to alarm.
The effective coverage radius of a combustible gas detector on a horizontal plane is preferably 7.5m indoors and 1.5m outdoors. For enhanced safety and effectiveness, the distance between detectors can be appropriately reduced based on site conditions.
Combustible gas detection and alarm can use single-stage or two-stage alarm. The first-stage alarm set point should be less than or equal to 25% LEL; the second-stage alarm set point should be less than or equal to 50% LEL. First-stage alarm can activate audible and visual alarms on-site or in the control room to alert relevant personnel; second-stage alarm can automatically start the on-site air supply/exhaust system to promptly remove combustible gas, keeping the on-site mixture concentration within a safe range.
The explosion-proof category of the detector must comply with the category, level, and group of the on-site explosive gas mixture. The selected detector's level and group should not be lower than the level and group of the explosive gas mixture in the installation environment.
Pharmaceutical enterprise explosion-proof workshops should install combustible gas alarm detectors. They can prevent fire and explosion accidents, greatly enhance production safety, reduce casualties, and minimize property loss for the enterprise, playing a significant role in safe production.
Enhanced Ventilation to Reduce Concentration of Explosive Gas Mixtures
Ventilation in explosion-proof workshops can be natural or mechanical. Natural ventilation involves opening workshop windows during production. Wind can carry away combustible gases, naturally reducing the concentration of explosive mixtures. Mechanical ventilation is typically designed by HVAC specialists, installing supply and exhaust fans in the workshop to improve the overall air condition.
Mechanical ventilation can be manually started for non-scheduled ventilation, or set with timers for scheduled ventilation. Additionally, it can be interlocked with the on-site or control room combustible gas detection alarm; when the set value is reached, the supply/exhaust fans start for ventilation. In summary, well-ventilated workshops can reduce the probability of explosion risks.
3. Conclusion
The electrical design for explosion-proof workshops in pharmaceutical enterprises should adopt corresponding preventive measures based on the characteristics of flammable and explosive substances and the basic conditions for forming an explosion, ensuring safety, rationality, and effectiveness. Only with reasonable design and standardized construction can the project meet explosion-proof requirements.
II. Explosion Relief Panels/Venting Panels Specialized for Chemical/Pharmaceutical Workshops
Venting buildings are used for areas with potential explosion risks. Such buildings can be separate or located along the exterior walls of a building, aiming to limit the area of facility damage.
The explosion venting wall system is designed to contain the internal deflagration closed explosion pressure and instantly release the critical pressure through venting devices. Note: Deflagration refers to the burning velocity of the explosive substance being less than the speed of sound (340.29 m/sec). System function: When deflagration occurs, and the shock wave and pressure reach 20 PSF (100 kg/㎡), the rupture of venting bolts promptly releases the shock wave and pressure to the outside, preventing damage to the building and other equipment, and maintaining the structural integrity of the building.
Design Standards: FM Global - Building Damage Limitation FM1-44; Code for Fire Protection Design of Buildings GB50016-2006. Application Scope: Chemical storage warehouses, Combustible gas solvent rooms. Venting Panels.
Characteristics of Explosion Venting Roofs:
Rapid venting
Minimal secondary injury risk during venting
Good strength
Lightweight
Durable
Moisture resistant
Compression resistant
Excellent fire performance
Quick installation
Outstanding thermal insulation performance
Mature leak-proof
Easy surface decoration
Parameters of Explosion Relief Panels:
Material composition: Minerals, fibers, additives, etc.
Combustion performance: Class A non-combustible material, according to GB8624-2006 non-combustible material
Size specification: 2440mm × 1220mm
Standard thickness: 6mm - 25mm
Density: 1000 kg/m³
Asbestos content: 100% asbestos-free
Anti-mold and anti-insect function: Under normal use conditions, possesses anti-mold and anti-insect functions.
Application Fields:
Explosion-proof venting roofs
Explosion-proof venting exterior walls
III. Explosion Protection Safety Management in Pharmaceutical Plants
In the design of pharmaceutical industrial plants, certain processes, such as chemical synthesis pharmaceuticals or the purification, drying, and packaging processes of active pharmaceutical ingredients, can easily pose risks and cause explosions.
Factors to Note in Pharmaceutical Plant Design for Explosion Protection
Workshops and production areas within a pharmaceutical plant that produce and use explosive materials should be concentrated and arranged within the same area as much as possible. The distance to general workshops and production areas should meet safety distance requirements, facilitating unified treatment of explosion-proof structures like firewalls.
Workshops with explosion risks should be arranged within single-story buildings. If the process requires a multi-story building, they should be placed on the top floor. When there are locally explosion-proof rooms within the plant, these rooms should be positioned against the exterior wall as much as possible, equipped with specially designed windows that open easily outwards. This facilitates achieving the required venting area and aids firefighting.
Within a plant building, workshops with high risks and those with low risks should also be separated by sturdy firewalls (brick or reinforced concrete walls). It is advisable to have doors on the exterior walls, using corridors or balconies for inter-workshop communication; or to install double-door airlocks in the firewall, preferably staggered, using the airlock to weaken the explosion shock wave and limit the affected area.
Areas within the clean zone requiring explosion protection should preferably be arranged against exterior walls, complying with the current national "Code for Fire Protection Design of Buildings" and "Code for Design of Electrical Installations in Explosive Atmospheres and Hazardous Areas".
Production and storage of hazardous materials of different natures should be set up separately, e.g., acetylene and oxygen must be separated.
Explosion hazard locations should not be set in basements or semi-basements, as poor ventilation can significantly impact accidents and is unfavorable for evacuation and rescue. Ventilation systems containing flammable and explosive substances should be set up separately, equipped with fire and explosion protection measures.
In explosive atmosphere environments, rooms requiring clean air should maintain positive pressure, while rooms emitting explosive hazardous substances should maintain negative pressure.
The following measures should be taken in process design to eliminate or reduce the generation and accumulation of flammable substances:
First, control the total amount of flammable substances; only the necessary usage amount should be placed in the production area.
The process flow should preferably use lower pressures and temperatures, confining flammable substances within sealed containers.
Nitrogen or other inert gas protection measures can be used inside equipment.
Promptly remove pharmaceutical residue discharged from production.
Flammable liquids must not be directly discharged into drains; water seals should be installed in drains.
Equipment using or processing flammable and explosive media in cleanrooms must meet both cleanliness requirements and fire/explosion protection requirements. Equipment and instrument maintenance and inspection should be performed well to eliminate leaks and spills.
Sealed device process equipment and pipelines are preferably arranged outdoors or in an open layout.
Electrical equipment in explosion-proof workshops should be selected and installed as explosion-proof types (e.g., explosion-proof switches, motors, luminaires, etc.) based on different situations. Non-explosion-proof equipment must be strictly avoided.
To eliminate or control sparks, arcs, or high temperatures sufficient to ignite explosive gas mixtures, the following measures can be taken:
For Class A production workshops emitting combustible gases heavier than air or flammable/combustible liquid vapors, and Class B production workshops with dust or fiber explosion risks, spark-free floors are preferable. To prevent sparks, floors can use rubber, plastic, rubber mixed with graphite, or asphalt concrete, etc. Interior walls in workshops where combustible dust might settle should be plastered or painted, creating easily cleanable (washable paint) interior surfaces.
Equipment and instruments directly located in areas with flammable liquids should be selected as explosion-proof types. Ventilation equipment exhausting flammable liquid vapors and vacuum pumps used for evacuation in areas with flammable liquids should be explosion-proof.
Control the flow velocity of conveyed flammable liquids to prevent static electricity generation.
Avoid friction and impact in areas with flammable liquids.
High-temperature equipment and pipelines should have electrostatic grounding devices to prevent static electricity generation.
Combustible materials should not be used as building materials.
Open flames are strictly prohibited in rooms with explosion risks.
Safety Alarms and Interlocks
In the safety protection measures for explosion-proof production areas, the rapid dispersal of explosive gases during accident conditions and the shutdown of ventilation systems during fire alarms to prevent fire spread must be considered. Therefore, the interlock logic in the ventilation interlock system design must be clear and unambiguous; otherwise, it may be counterproductive.
Install explosive gas concentration probes in locations within the production workshop most likely to leak. Once the concentration exceeds the alarm threshold, automatically send a signal to interlock and start the emergency exhaust in the ventilation system, increasing exhaust volume to rapidly reduce concentration. In case of a fire, automatic smoke detection systems or manual fire alarm buttons should automatically interlock to shut down the running ventilation system to prevent fire spread.
Safety Interlocks: Electric heaters in HVAC systems should be interlocked with supply fans and should have no-air-flow power cut-off and over-temperature power cut-off protection devices. Pneumatic actuators are used in conjunction with regulating water valves and air dampers in flammable and explosive environments.
