Hazardous Area Classification by Risk Evaluation (Based on IEC 60079-10-1Edition 3.0)
In 2020, IEC (International Electrotechnical Commission) standard 60079 Part 10-1 "Classification of areas-Explosive gas atmospheres" published as IEC 60079-10-1 Edition 3.0 (hereinafter calls as IEC Ed 3.0).
This third edition of IEC 60079-10-1 cancels and replaces the second edition, published in 2015, and constitutes a technical revision.
The hazardous area classification according to IEC Ed 3.0 has promoted expansion of the use of electric devices such as smartphones, tablets and drones in the hazardous facilities and DX (Digital Transformation). Recently new needs are increasing. For example, consideration of ventilation methods and allowable leakage volumes to secure non-hazardous areas (non-explosion-proof areas) for equipment that cannot be used with explosion-proof, expanding areas for hot works and workload shift from turnaround to daily maintenance, and so on.
FPEC will evaluates and determine explosion proof areas for facilities handling hazardous materials according to IEC Ed 3.0.
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Previous method to determine the explosion proof area
The explosion-proof area was used to be determined according to the sample figures shown below based on API RP500, or 505 and NFPA497.
API 500 NFPA 497 -
IEC Ed.3.0 method
Compared to the previous method, the method of determination of explosion proof area had drastically changed. What used to be a sample figures as published by the NFPA and API had been changed to a method of individually risk assessment by quantifying the amount of leakage and the degree of diffusion. Until now, since the sample figures described above was used, if it is a flammable dangerous substance, the dangerous zone is set almost uniformly, not limited to the evaluation of its vapor pressure, molecular weight, and possibility of leakage. Therefore, the entire section with plant equipment was often set as a dangerous area.
IEC Ed 3.0 presents criteria for evaluating risk (suggested values of ventilation level such as leak size and wind), evaluates risk for each case, and determines whether it is a hazardous or a non-hazardous area. This has made it possible, and as a result, the range of non-hazardous areas has often increased. If it is determined to be a hazardous area, the range (hazardous distance) can also be read from the graph.
Applicable Scope of Hazardous Area Classification
We perform risk evaluation for items and complex conditions for which specific calculation methods are not described in IEC Ed3.0 by conducting engineering studies such as chemical engineering, thermodynamics, fluid dynamics, etc.
Item | FPEC coverage | Explanation |
1.Evaluable substances |
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2.Source of release |
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3.Outdoor/Indoor |
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4.Boiling / Non-Boiling liquid |
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5.Supported Industries |
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Application to actual analysis
- Since the case released in the gas state can be easily calculated according to the standard, the risk evaluation could be carried out without much difficulty.
- The case that liquid leaks, liquid pool is made on the ground and liquid evaporates is difficult.
- For the cases that liquid pool is non-boiling and no thermodynamic input is required from the surface on which the liquid is spilt
- Since the evaporation rate calculation is based on mass transfer calculation by wind, we calculate the evaporation rate based on the formula specified by IEC Ed 3.0.
- We set the leakage duration in this case according to the actual conditions such as process conditions and on-site patrol with reference to API.
- For the cases that liquid pool is boiling, or thermodynamic input is required from the surface on which the liquid is spilt
- Since IEC Ed3.0 does not stipulate the evaporation rate regarding boiling liquids and thermodynamic input, we calculate it with heat balance calculation methods with solar heat, atmosphere, ground, etc. adopted by the ALOHA program developed by U.S. NOAA (National Oceanic & Atmospheric Administration) and EPA (Environmental Protection Agency).
- Since IEC Ed3.0 does not stipulate the evaporation rate regarding boiling liquids and thermodynamic input, we calculate it with heat balance calculation methods with solar heat, atmosphere, ground, etc. adopted by the ALOHA program developed by U.S. NOAA (National Oceanic & Atmospheric Administration) and EPA (Environmental Protection Agency).
- For the cases that leaked liquid is flashed
- Since IEC Ed3.0 does not stipulate the evaporation rate in this case as above, we calculate flash rate with flash calculation and evaporation rate of the remaining liquid pool with heat balance calculation methods. Note that the hazardous distance cannot be calculated unless the amount of flash gas and evaporative gas are separately calculated.
- Since IEC Ed3.0 does not stipulate the evaporation rate in this case as above, we calculate flash rate with flash calculation and evaporation rate of the remaining liquid pool with heat balance calculation methods. Note that the hazardous distance cannot be calculated unless the amount of flash gas and evaporative gas are separately calculated.
- For the cases that liquid pool is non-boiling and no thermodynamic input is required from the surface on which the liquid is spilt
- Estimating the physical properties of leaked liquids are also important for the risk assessment. The properties must be calculated at each temperature and physical property estimation method must also be utilized.
- Pure component liquid
- Specific heat at constant pressure of gas and liquid, specific heat ratio, density, latent heat of vaporization, vapor pressure, etc.
- Vapor pressure is calculated from the Antoine coefficient.
- Multiple component liquid
It is more complicated, since compositional variations must be considered.
- Specific heat at constant pressure of gas and liquid, specific heat ratio, compression factor, density, latent heat of vaporization, vapor pressure, molecular weight, lower explosion limit(LEL), boiling point, liquid composition, etc.
- For the vapor pressure, the partial pressure of each component is calculated from the Antoine coefficient, and Raoult's law is applied to obtain the partial pressure of the multicomponent system.
- The LEL is calculated by Le Chatelier's law.
- If the multiple component liquid contains water, the flash and evaporation calculations must include water in the calculations, but the properties such as molecular weight, gas density, LEL and the calculation of the volumetric release characteristic of the source must exclude water.
- Pure component liquid
- Regarding leakage from flanges, IEC Ed 3.0 indicates the range of the leakage port area, but we divide the range into 4 parts based on the (operating pressure / rated pressure) ratio and determine the appropriate value.
- The suggested value of the leak port area differs depending on whether or not the leak port area may expand in the event of a leak, but we decided it in consideration of the maintenance conditions, the age of plant construction, operating pressure, in sound velocity or not, etc.
- If the outdoor ventilation velocities are applied form actual measured values, it should be assessed as the velocity that is exceeded 95% of the time by IEC Ed3.0. Note that applying mean wind velocity as the ventilation velocity may underestimate the risk evaluation.
- Hazardous area
- Spatial shape
The spatial shape of the hazardous area for each release source is determined by selecting from the spatial shapes of hazardous areas defined by IEC Ed3.0 according to the leakage and evaporation conditions of the leaked liquid.
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3D display on plot plans
We allocate the spatial shapes of the hazardous areas on 3D or 2D plot plan.By superimposing the areas of individual release sources, you can learn the hazardous areas of the entire facility, and clearly determine zones where non-explosion-proof equipment can be used according to the actual operation of the facility.
It is also used for safe flight planning of drones and is expected to be used in fields where spatial position information is required, such as automatic flight functions in the future.
Some samples are shown below.
[3D display on 3D plot plan]
[3D display on 2D plot plan]
[2D display on 2D plot plan]
- Spatial shape
- Since primary grades of releases are various depending on how to handle hazardous materials, the rate of gas release or evaporation must be calculated on a case-by-case basis.
[Evaluation examples for primary grades of releases]
- Tank vent
- Assumed that the little remaining liquid is in vapor-liquid equilibrium at that temperature when a tank is almost empty and the gas volume is maximum. The heat balance with solar heat to a tank roof and a sidewall, radiant heat from the tank, convective heat transfer by wind, etc.is calculated. The rate of temperature rise in the gas phase in the tank is calculated, and then the release rate of the vent gas is obtained from the volume expansion rate of the gas phase.
The solar heat is determined by the latitude and longitude of the location of the tank, the date, and the altitude of the sun. By calculating the change over time in the gas release rates, we can learn the change in the hazardous area over time. - In the case that the gas volume is almost zero such as a floating roof tank, it is assumed that the input heat through the sidewall of the tank is calculated, and then internal liquid is heated by the heat.
Assumed that input heat is used for the whole liquid temperature rise until the temperature of the sidewall reaches the boiling point of the liquid and then the vaporization when it reaches the boiling point. The gas release rate uses the evaporation rate of the liquid on the boiling point.
As above, by calculating the change over time of the altitude of the sun, we can learn the change in the hazardous area over time.
- Assumed that the little remaining liquid is in vapor-liquid equilibrium at that temperature when a tank is almost empty and the gas volume is maximum. The heat balance with solar heat to a tank roof and a sidewall, radiant heat from the tank, convective heat transfer by wind, etc.is calculated. The rate of temperature rise in the gas phase in the tank is calculated, and then the release rate of the vent gas is obtained from the volume expansion rate of the gas phase.
- Evaporation from open surfaces
When evaporating from a liquid surface that is open to the atmosphere, check the operating conditions of the liquid and the presence or absence of wind on the liquid surface (e.g. if the liquid surface is deep in the containers, less wind blows.), and then determine the gas release rate by mass transfer calculation or heat balance calculation. - Evaporation from painted surfaces
Assumed that a paint is applied evenly at one time on the painted surface, and then volatile components evaporate from the surface. As a risk assessment, this is the maximum rate of gas release and will be considered as a stricter assessment. - Mixing liquids in open vessels
Assumed that the most volatile liquid (liquid 1) is in the open vessel and then the other liquid (liquid 2) is poured in it. So, the evaporated gas from the liquid 1 is released with the same volume of the liquid 2 poured from the vessel.
The gas release rate in this case is determined by the concentration of the gas evaporated from the liquid 1, the poured volume and poured duration of the liquid 2.
- Tank vent
- In any case, it is important to show how to determine the values in the risk assessment as required by IEC Ed 3.0.
We summarize the risk evaluation results in the table below for each assessment case, and the details of the risk evaluation are clearly recorded. (Below example is LPG equipment)
Experiences
The industries that we have supported and consulted with so far are as follows. If you have equipment that handles flammable liquids or gases, you can take advantage of our precise risk assessment of hazardous areas. If you are specifically considering reviewing your explosion-proof area, please contact us.
- Petroleum Products Plants
- Petrochemical Plants
- Oil Terminals
- Various chemical manufacturing plants
- Plastic Molding Plants
- Semiconductor related plants
- GX (hydrogen, etc.)
- Paint shops
- Paint and Ink manufacturing plants, Printing plants.
- Cleaning process with organic solvents
- Airport Refueling Facilities (Aircraft Refueling Facilities in Kansai International Airports)
- Research Institutes, etc.
Examples of Use
This risk assessment is used in the following cases. If you are thinking of using non-explosion-proof equipment or reviewing hazardous areas at hazardous materials facilities, please take advantage of our precise risk assessment of hazardous areas.
- Expanding the range of use of portable non-explosion-proof devices such as smartphones and tablets
Smartphones and tablet terminals have been introduced to improve the efficiency and reduce the burden of on-site work, such as viewing information at the site, sharing and reporting information immediately, and digitizing work records, and to ensure the safety of workers by carrying vital sensors. - Expanding the area where sensors and cameras are installed
By installing sensors and cameras at the site and continuously acquiring information, it is possible to automate and digitize data of work that was previously performed by workers. The data obtained can be analyzed and diagnosed to detect abnormalities at an early stage and help prevent accidents and malfunctions. In addition, alert functions by intrusion detection can be used to prevent accidental intrusion into hazardous areas. - Consideration of conditions for securing non-hazardous areas (non-explosion-proof areas)
Conditions for securing non-hazardous areas (such as necessary ventilation conditions and allowable leakage volumes) can be studied, and fixed equipment that cannot be explosion-proof can be installed. - Expansion of hot work areas and leveling of maintenance work
Expanding the non-hazardous area will allow for hot work in routine maintenance, resulting in a reduced burden of turnaround maintenance and leveling of maintenance work. - Promoting the use of drones
There is a need to use drones in hazardous material facilities as an alternative to inspection work in high places that require scaffolding, etc. and for diagnosis of abnormalities by image analysis of on-board cameras. - Reduction of maintenance costs
By expanding the non-hazardous area, inexpensive non-explosion-proof equipment can be selected when updating equipment, etc. contributing to reduction of maintenance costs.
Materials required for evaluation
For the evaluation, we ask you to provide us with the following materials.
- Plot plan
- Information on the hazardous materials to be assessed (including physical properties such as composition, molecular weight, boiling point, vapor pressure, lower explosive limit, etc.)
- Operating conditions (any documents showing fluid name, operating pressure, operating temperature conditions, etc)
- P&IDs
- Piping service classes
- Datasheets of tanks
- Equipment list for rotating machinery such as pumps
- Any materials showing the ventilation in buildings (ventilation equipment, air flow, etc.)
- Overall drawings or flow sheets of local exhaust system
- Others (We may ask you to provide additional materials depending on what is being considered.)