Ventilation Measures Against Industrial Explosions in Paint Production Facilities

Summary

Based on Occupational Health and Safety Law No. 6331, the "Occupational Health and Safety Risk Assessment Regulation" stipulates in Article 8, paragraph 1, clause (r), and furthermore, the "Regulation on the Protection of Workers from the Dangers of Explosive Atmospheres" issued under the same law requires in Article 10 that workplaces where there is a possibility of explosive atmosphere formation must prepare an "Explosion Protection Document." This document expresses in written form how explosion risk is managed in that workplace. When managing explosion risk in workplaces, the most prioritized measure to be applied is naturally the prevention of explosive atmosphere formation. If an effective ventilation system is present, the formation of a flammable fuel and air mixture can be prevented. The effectiveness of the ventilation system should be evaluated together with the operability of the system and the duration that the flammable fuel and air mixture remains in the environment. Standard TS EN 60079-10-1:2015 defines the methodology to be followed regarding the classification of hazardous zones in explosive gas atmospheres and the application of this assessment. When process conditions are evaluated within the framework of this methodology, the problems encountered, the assessment of ventilation system effectiveness, the selection of electrical equipment complying with hazard classification in ventilation systems to be operated in explosive atmospheres, and additional solution resources are presented in this work.

1. Introduction

In a process using hazardous chemicals, dispersion in gaseous phase occurs in the working environment and/or atmosphere. If the chemical in question has flammable or oxidizing properties, there is a possibility of explosion of the air + chemical mixture that will form in the working environment. The lower explosion limit value found in the chemical's safety data sheet means that the gas can form an explosive mixture with air. For example, during battery charging, hydrogen gas is released into the environment. If the mixture of hydrogen gas constituting four percent of the environmental volume with the air in that volume meets sufficient ignition energy, it will explode. As a result of this explosion, workers, equipment, and the building where the process is occurring will be damaged. The numerical values of physical properties in a chemical's material safety data sheet are determined in laboratory conditions or under controlled ideal conditions. Therefore, the numerical value indicated as the lower explosion limit will decrease or increase depending on the ambient temperature and pressure. At the same time, the ignition temperature at which the flammable chemical creates a brief flame pocket may also vary according to environmental conditions, and combustion may continue below the lower combustion limit, causing an explosion to occur. In the "Regulation on the Protection of Workers from the Dangers of Explosive Atmospheres," the mixture created by gases, vapors, mists, and dusts of flammable materials with air under atmospheric conditions, which is completely combustible upon contact with any ignition source, is defined as an explosive atmosphere. According to the European Parliament and Council Directive dated 6 December 1999 and numbered 1999/92/EC, and as published by the Turkish Standards Institute in the standard TS EN 60079-10-1:2015 Explosive Atmospheres - Part 10-1: Classification of Hazardous Zones - Explosive Gas Atmospheres, under conditions where flammable chemicals are regularly released into the working environment as required by the process, a value equal to 25 percent of the lower explosion limit is defined as the safe value [1]. Explosive atmosphere formation from gas or liquid release can be drawn to safe levels by ventilation, especially by mechanical ventilation. Depending on ventilation effectiveness, the hazardous zone is determined as follows: • Determination of the order of magnitude of minimum ventilation rate required to prevent serious accumulation of explosive gas atmosphere, • Calculation of ventilation speed and vapor dispersion characteristics and dilution, • Determination of the order of magnitude of persistence time of vapor in the environment, • Identification of the hazardous zone using ventilation dilution effectiveness, operability, and the duration of explosive atmosphere remaining in the working area values, • Verification that the hazardous zone is consistent with persistence time. • The following may be achieved through mechanical ventilation: • Determination of the hazardous zone as a less hazardous zone and reduction in dispersion limits, • Reduction in persistence duration of explosive gas atmospheres, • Prevention of explosive gas atmosphere formation. • A mechanical ventilation system designed for explosion prevention shall meet the following conditions: • Its effectiveness shall be checked and monitored. • The classification inside the extraction system and at the discharge point of the extraction system and just outside other openings of the extraction system shall be taken into account. • Ventilation air for hazardous zone ventilation should normally be drawn from a non-hazardous area, and the suction effect on the surrounding area shall be considered. • Before the ventilation system dimensions and design are determined, the location, degree, and speed of the release shall be identified. Additionally, the following factors affect ventilation system quality: • Flammable gases and vapors generally have higher densities than air. Therefore, they tend to accumulate near the floor or ceiling of enclosed areas. Air movement is quite limited in these locations. • Gas density varies with temperature. • Obstacles can reduce or completely stop air movement. Therefore, some parts of the zone may not have ventilation. The effectiveness of the ventilation system regarding the dispersion and persistence of explosive gas atmosphere depends on the degree and operability of ventilation and the system design. For example, a ventilation system may not be sufficient to prevent the formation of explosive gas atmosphere but may be sufficient to prevent its persistence. If the presence of explosive atmosphere in the working area cannot be prevented, all energized equipment and machinery must be made suitable for the explosive atmosphere. Energized equipment does not only refer to electrical energy; pneumatic systems and systems that conduct liquid and gas fluids should be evaluated as energized systems since they generate static electricity on piping. Static electricity does not only occur on equipment. During a working day, workers can be charged to create potential differences rising to 15,000 volts or even up to 30,000 volts during routine activities. Therefore, this energy must be controlled. Grounding installations, grounding connections, and equipotential connections can provide this control. If this control is not provided, the gas or vapor forming the explosive atmosphere dispersed in the working area will ignite and an explosion will occur.

2. Material and Method

In preparing this work, the findings encountered by the author in the preparation of explosion protection documents previously carried out were compiled. Dye production facilities typically consist of raw material storage, initial mixing, pigment/paste preparation, formula completion, packaging filling, and product storage sections. The work explains how the explosion risk values resulting from operations in these areas should be reduced with the ventilation system. These findings obtained from actual facilities and real working conditions were evaluated in a flow determined by the legal regulations.

3. Results

How much the mixture determined as an explosive atmosphere will spread in the working environment is evaluated by the dilution effectiveness of the ventilation system. The function between the flow rate, density, lower combustion limit, and safety factor of the gas or flammable liquid vapor released into the environment determines the characteristics of ventilation. The relationship between ventilation characteristics and air velocity in the environment determines the dilution degree of the ventilation system. The ventilation degree is defined as high, medium, or low in the relevant standard.

High Dilution:

This occurs in areas where the air change rate is high and the working volume is small. Keeping the working area where explosive atmosphere formation is expected small can be considered as a measure.

Medium Ventilation:

This refers to situations where ventilation can dilute flammable liquid vapor to a certain level, but it cannot be completely removed from the environment due to factors such as physical obstacles in the working area, ambient air temperature, and ambient air pressure. In these environments, measures against all ignition sources, including static electricity, shall be implemented.

Low Ventilation:

This refers to situations where the ventilation system cannot dilute explosive atmosphere. Changes including engineering solutions on the process should be evaluated. The efficiency of ventilation in terms of dilution effectiveness of explosive gas atmosphere is expressed by the f-value. This f-value typically varies between f=1 (ideal condition) and f=5 (obstructed air flow). Therefore, in a ventilation system, the location and shape of outlets at the ends of ducts and the presence of obstacles in front of outlets are extremely important. Specifically, a change in the f-value means that the air flow rate that should be supplied to the environment changes by a multiple. The air change rate per unit time C, together with the ventilation effectiveness coefficient, directly affects dilution effectiveness. As the air change rate increases, dilution of the chemical released into the environment occurs more quickly. When calculating how much gas can be released into the environment as a result of a failure in the flanged section of a chemical in gaseous phase transmitted in piping under pressure, the following equation is used: In this equation, the area S of the section where dispersion occurs, the pressure p in the piping, and the polytropic index value expressing the dispersion capability of the gas are determining factors. As can be seen, conditions dependent on the ventilation system are not included in the equation. Under normal operating conditions, if handling operations are not carried out in a building storing flammable materials, such as taking samples or transferring chemicals from large barrels to smaller containers, chemical release is not expected. Therefore, explosive atmosphere formation is not expected. However, Article 118 of the "Regulation on Fire Protection of Buildings" defines volumes where flammable and flashpoint chemicals are stored as Zone 1 (hazardous zone). In such a storage facility, while operations are conducted under normal conditions as mentioned above, chemical release can be expected secondarily due to spills formed on the floor or spills that will occur on the floor as a result of overturning during transport. The following equation can be used to calculate the amount of free dispersion at atmospheric pressure, i.e., evaporation occurring on the floor [2]: In this equation, the uw value is the air velocity value acting on the surface of the released chemical. High air velocity increases the evaporation rate linearly, and therefore, to keep the concentration of the released chemical below the explosion range, air must be supplied to the environment at a higher rate. If the duct cross-section and outlet cross-section are not properly sized, air velocity will increase. Together with the ventilation dilution degree, the conditions enabling the ventilation system to operate continuously and the continuity of dispersion in the process can be evaluated together to determine the hazard classification of equipment to be used in the working environment. The matrix in Table 1 is a tool that can be used for this evaluation. The hazardous zone found using Table 1 should not be the final result. It is necessary to know how long it takes for the chemical released into the environment to be diluted to a safe concentration value after dispersion ceases. In practice, if chemical release does not dilute for more than 15 minutes, that release should be considered permanent. The persistence of a chemical release can be calculated with the following equation: The Xb and Xc values in the equation are concentration values used when determining the ventilation effectiveness coefficient, and are used in determining that the ventilation flow rate is effectively delivered to the environment, and these values should be confirmed by measurements to be performed in the environmental volume. Concentration values and air change rate (C) are factors directly affecting persistence time. Outlet placement and system flow rate must be correctly and adequately determined.

3.1. The Effect of Environmental Conditions in Determining Explosion Severity

Trinitrotoluene (TNT) has been used for a long time in mining, road opening, and military ammunition. Therefore, since there is sufficient research on TNT explosions and their effects, it is possible to calculate values such as the energy that would result from an explosion of a fuel vapor + air mixture and the pressure increase in the blast impact range using the "TNT Equivalent Model" [3]. Using the equation determined by this equation, the pressure increase value that will affect a person, equipment, or building located at the determined range can be calculated. In this equation, the Z-value represents the scaled range value. In order to calculate the scaled range value, the mass of the released chemical must be calculated and reduced to its TNT equivalent. The volume of the chemical vapor + air mixture released into the working environment can be calculated. If the partial pressure value of the vapor of this chemical is known, the molar value of the chemical forming that volume is calculated using the ideal gas equation, and then using the specific weight value of the chemical, how much mass in that volume corresponds to the chemical is found. When using this method, which partial pressure value should be selected depends on the working environment temperature and pressure, so maintaining stable working values of the ventilation system and monitoring them by measurements is extremely important. Fluctuations in the working environment air resulting from conditions caused by the ventilation system directly affect the severity of a possible explosion and can cause increased damage. When determining measures against the damage expected to be caused by an explosion, a consistently operating system and its associated data will affect the correctness of the design. Table 2 shows what kind of damage the pressure increase caused by an explosion corresponds to.

4. Discussion, Conclusion, and Recommendations

Prevention of explosive atmosphere formation or its dilution to a safe concentration value in a short time can be achieved with an adequately sized and correctly designed ventilation system. A high air change rate (C) directly affects system flow rate and consequently the size of the motor supplying energy to the system. High air velocity (u) increases the danger posed by released chemicals. The duct and outlet should not be selected as narrow, but the optimum value should be considered in terms of cost. Incorrect outlet placement or irregular motor operation of the system changes the ventilation effectiveness value (f). Any change in the ventilation effectiveness value will cause air flow to increase by a multiple. The outlet should be correctly and freely placed. In practice, particularly in areas where initial mixing operations are conducted in paint production facilities, and in pigment/paste preparation and formula completion areas, the required cost for electrical equipment such as mixer motor, circulation pump motor, control panel, outlet, switch, and lighting fixture to be suitable for, for example, Zone 2 hazardous zone is 1 unit, while the required cost for Zone 1 hazardous zone can differ up to 5 units. Improperly sized and placed ducts and outlets and a ventilation system with insufficient flow rate capacity will significantly increase the cost of electrical equipment to be operated in hazardous zones. Lecturer Dr. Serdar Gültek / Property Protection and Security Department / Istanbul University Technical Sciences Vocational School

5. References [1] TS EN 60079-10-1:2015 Explosive Atmospheres - Part 10-1: Classification of Hazardous Zones - Explosive Gas Atmospheres, Turkish Standards Institute, December 2015. [2] Zalosh, R., "Industrial Fire Protection Engineering", Wiley, 2003. [3] Guidelines for Chemical Process Quantitative Risk Analysis, American Institute of Chemical Engineers, 2001. [4] Areal Locations of Hazardous Atmospheres Software, Technical Documentation, United States Department of Commerce, 2013.