Identifying and Preventing Dust Fire and Explosion Hazards Warren Greenfield International Specialty Products Wayne, New Jersey ABSTRACT This paper discusses how International Specialty Products Inc. addresses the identification and prevention of dust explosion hazards in their facilities. The need and methods to obtain required process safety information is discussed and an approach to reduce risk at the operating facilities is presented. Current activities as well as future plans are presented for obtaining process safety information as well as for implementing a protocol for conducting safety reviews and risk assessments for hazardous powder/dust systems. In addition to being informative for the technical personnel already doing work in this area this paper could provide insight and concepts to companies with limited resources who want to be more active in hazardous dust powder process safety screening activities. 1. INTRODUCTION International Specialty Products develops and manufactures specialty chemicals for a diverse range of industries. Over 300 products are produced for use in the pharmaceutical, hair and skin care, food ingredients, agricultural, elastomers and coatings and adhesive markets. The diversified product lines include a range of monomers and polymers which are produced through batch, semi-continuous and continuous processing. International Specialty Products is committed to supporting the development of effective practices and approaches to control workplace risk for all of its manufacturing sites. One important aspect of this commitment is the obtaining and application of process safety information (PSI) to be utilized in defining and minimizing process hazards while processing hazardous dusts and powders. ISP s Process Safety Laboratory in Wayne, New Jersey is a major source of this type of process safety information for the company. A second important aspect of this commitment is the utilization of Process Hazards Analysis methodology coupled with a risk analysis component to identify existing risks and the resulting risk after additional mitigation efforts are made.
International Specialty Products operates both continuous and batch facilities. Most of the powder processing activities occur in the batch operations. Powders can be a raw material, intermediate or a finished product. The vast majority of these powders are organic powders and several contain nitrogen atoms in their chemical composition. In addition to storage, loading and packaging of these organic powder materials there are also various types of drying, size reduction, screening, blending, conveying, and dust control activities. In the past the determination of the hazardous characteristics and the application of the PSI to the design and operation of the operating systems have been dependent on individual plant practices. Recently, a Corporate Safety Health Practice (SHP) has been developed which will require all facilities to follow a specific protocol when processing hazardous powders and dusts. This protocol will define the testing that should be performed on the powders to define their hazardous characteristics and an approach for conducting a safety review and risk assessment for ensuring operations provide adequate risk protection. The SHP in its simplest form has four major steps in the process. The first major step is to characterize the material to determine if the powder /dust is combustible. For materials found to be combustible, the second major step is to determine the hazardous characteristic data (PSI) required to perform a process hazard analysis and risk assessment on the system. These characteristics include the minimum explosive concentration, the minimum ignition energy of a dust cloud and the Kst of the material. Often, the limiting oxygen concentration and the minimum autoignition temperature of a dust cloud and dust layer are also obtained. The other characteristic that will always be evaluated is the self heating potential of the material. The third major step is to do the PHA and risk assessment. If the risk is found to be unacceptable then a fourth major step which is risk mitigation would be required. Steps 1 and 2 are normally provided by the ISP Process Safety Laboratory in Wayne but outside facilities are also utilized when necessary. 2. Wayne Process Safety Laboratory-Overview The Wayne Process Safety Laboratory s main function is to develop and provide process safety information to all of ISP. The information is utilized in PHA s, risk assessment, establishing safe operating boundaries and in equipment and safety relief design. Specifically for powders and dusts the following services are provided: - Determination of explosion characteristics of powders and dusts and gases - Evaluation of the thermal stability of powders and dusts - Evaluation of the self-heating characteristics of powders and dusts The equipment that is normally utilized in the powder/dust testing consists of: - Grewer Oven-Self-Heat Screening and auto ignition temperature in an air stream - Falling Hammer-Impact Sensitivity ASTM E680
- Mike 3 - Minimum Ignition Energy of a Dust Cloud ASTM E2019-20L Sphere -Pressure and Rate of Pressure Rise for Combustible Dusts (P max, dp/dt max, K st ) ASTM E1226 - Minimum Explosible Concentration of Combustible Dusts ASTM E1515 -Limiting Oxygen Concentration - Flammability of solvents and gases -Dust layer ignition temperature apparatus-hot Surface Ignition Temperature of a dust Layer ASTM E2021 - VSP2 adiabatic calorimeter- self heat screening and thermal stability 3. PHA and Risk Assessment Methodology ISP has developed and issued a SHP to define and establish a consistent approach and methodology for when and how to conduct a PHA and risk assessment for processing combustible powders and dusts. The objective is to reduce the risk to ISP personnel and facilities that are working with these types of materials The hazards associated with combustible materials can be fire or explosion hazards of the particulates in either bulk form, layer form or in the form of a suspended dust cloud. Reactivity hazards and toxicity hazards can also be present but are not addressed under this protocol. The major steps 3 and 4 address the PHA and risk assessment portion of the protocol. The fire case scenarios require the three components of the fire triangle. These are a fuel, an oxidant source and an ignition source. The fuel and oxidant need to be present in the proper concentrations and the ignition source needs to have sufficient energy for the fire to occur. The explosion scenario involves two additional items. The first is mixing or turbulence, and the second item is confinement. The SHP utilizes a PHA which focuses on the major fire and explosion hazards. The PHA will focus on developing scenarios that could result in fires and explosions if adequate mitigation were not in place. The risk assessment is performed utilizing a layer of protection analysis (LOPA) which is a semi quantitative approach to risk assessment. ISP has utilized the LOPA approach in their corporate risk assessment and mitigation procedure and it has been extended to powder and dust applications in the new SHP. The LOPA evaluates what the risk level is and what mitigation will be necessary to achieve an acceptable level of risk per the company standard.
The basic steps which are subsets of the four major steps in the SHP are: 1. Ascertain by literature search or testing that the powder/dust material is combustible. If the material is combustible all of the required process safety information (PSI) should be determined. 2. Identify the nodes or different systems that have to be evaluated. These can usually be derived from analyzing: a. charging of material operations-including drum /container handling b. transfer of material operations-air conveyors, screw conveyor, bucket elevators, etc c. processing steps i- drying ii- milling iii- screening iv- blending d. storage of material- both short and long term e. dust control systems-dust collection ducting, bag houses, cyclones, scrubbers, etc. 3. Collect PSI pertaining to the equipment. Include the equipment dimensions of the processing equipment, the MAWP of the processing equipment, the materials of construction of the processing equipment, P & ID s for the processing system being evaluated, all pertinent area electrical classification specifications, and reports documenting grounding and bonding test results. Also the dimensions and physical characterizations of the operating areas/processing rooms (such as drop ceilings) should be gathered. 4. Gather all process information including both normal conditions and extreme deviation conditions 5. Determine if the potential for an explosion or fire can be present for each of the nodes/systems previously identified. All possible deviations without applying safeguards should be used for the initial scenario development. 6. Differentiate explosions between primary explosions, propagating explosions and secondary explosions utilizing the appropriate guide lines found in the SHP. 7. Differentiate fire between spreading fire (spreading on powder or spreading on other materials), flash fire, or smoldering fire utilizing the appropriate guide lines found in the SHP.
8. Evaluate the presence of ignition sources of sufficient energy to initiate the event utilizing the guidelines in the SHP for ignition sources. 9. Perform a LOPA by analyzing and evaluating the existing layers of protection to reduce the risk of hazards determined in steps 5 through8. This is done utilizing the guidelines in the SHP on how to apply LOPA to the PHA. 10. Complete the LOPA by determining what additional layers of protection are needed to achieve an acceptable level of risk for operations. 12. Documentation should include all the PSI gathered, scenarios developed and evaluated, LOPA documentation and the action plan. The action plan should include all required follow up activities with indication of the responsible person and due date for the action item. On the following pages are two representative figures. One is an example of a risk matrix. Companies utilizing this method must develop a matrix that is acceptable and compatible with their standards and requirements. The second figure is an example of a summary table which can be used to document the results of the PHA/LOPA process. Each scenario evaluated should be documented. In some cases individual LOPA sheets are used for each scenario and the summary is presented in a table such as this. The use of individual LOPA sheets allows more room for documenting issues and can incorporate step by step directions on the LOPA procedure into the sheet. Every company will have some slightly different interpretation of the areas on their risk matrix depending on how they constructed their risk matrix. Typically, the red areas of the risk matrix signify areas of high risk and would signify the need for more mitigation or protection to lower the risk. The green areas depict acceptable or desired risk levels. The yellow areas typically signify areas where the risk level is tolerable but should be evaluated for additional cost effective risk mitigation when possible. The risk matrix is a key tool in the LOPA methodology. After a scenario is developed, the consequence is determined and if the consequence is significant a risk analysis using LOPA is done. To do the risk analysis the frequency of the initiating event for the scenario must be determined. The frequency is determined utilizing corporate guidelines. Now with a specific consequence and frequency defined a position on the risk matrix can be located. If the initial placement is in an area of unacceptable risk the existing safeguards are evaluated to determine if the risk is now acceptable. If the risk is still not acceptable additional efforts are made to mitigate the risk further. The SHP that ISP has developed contains several attachments which provide guidance for characterizing the consequence, ignition
energies and source types (including self heating), initiating/enabling frequencies, and credits allowed for different types of mitigation efforts. At ISP, initial training sessions on the hazards of dust/powders coupled with the new SHP for conducting PHA/LOPA for powder and dusts have been conducted. Several additional training sessions are envisioned which will incorporate feedback from the initial sessions and the initial attempts to utilize the SHP. An example application of the SHP application follows. Example case- background A PHA is conducted on a double cone rotary dryer. The dryer is processing an organic powder that is found to be combustible. The powder has a very low minimum ignition energy (~5 mj), a minimum explosion concentration of 40 g/m 3, a P max of 8 bar and a K st of 150 bar-m/sec. The drying operation is normally conducted under vacuum. There is a nitrogen system that supplies nitrogen to the dryer if the vacuum is lost. The dryer has a MAWP of 1 bar. PHA/LOPA The PHA team concludes that if the seal is lost due to a gasket leak air will leak into the system and a combustible dust cloud could form. Following the SHP guidelines the consequence of this could be a primary explosion inside the dryer which would be a consequence category of IV. This consequence was selected because this dryer is in an area where operators are located and personal injury could occur. The frequency is determined by the initiating event and the enabling event. In this case the frequency of failure of a standard gasket was 0.1 yr -1 and the enabling event was an ignition source which was assumed to be always present. Thus, the enabling factor was 1.These factors would be obtained from the guidance in the policy. The very low MIE made this system very susceptible to ignition by several types of electrostatic discharges and a conservative approach was taken. LOPA protocols are typically skewed to take a more conservative approach. The position on the risk matrix falls in the red area. The risk matrix indicates that two credits are required to move into the tolerable risk area. The team then reviews existing safe guards and the existing nitrogen system for protection against air leakage. Since this is a basic process control system, the policy allows 1 credit for this. There is still a need for more risk mitigation. A suggestion that a pressure relief panel be installed was made but because of the nature of the equipment this was not a viable option. After discussion it was decided that an explosion suppression system would be added to the dryer. The credits allowed per the SHP for the suppression system would now bring the risk level to the tolerable level. This scenario would now be written up and documented and the next scenario would be evaluated.
A general risk matrix used in LOPA evaluations is: Frequency of Consequence (Year -1 ) I II III IV V 10 0 Consequence Category 10-0 10-1 10-1 10-2 10-2 10-3 10-3 10-4 10-4 10-5 10-5 10-6 10-6 10-7
A sample PHA/LOPA template page is:
4. SUMMARY This paper presented and discussed a Safety Health Practice (SHP) which ISP is utilizing to analyze and reduce risk when processing hazardous powders and dusts in their facilities. An overview of the ISP S Wayne Process Safety Laboratory s capability for obtaining the required process safety information as well as an example of the PHA and risk assessment methodology has been discussed. It is envisioned that this information will be helpful to those who are interested in developing a system for evaluating and reducing risks associated with powders and dusts as well as provide insight to some of the supporting information that is required to support the PHA/LOPA analysis.