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A Summary of the Reissued OSHA Combustible Dust NEP

On October 18, 2007, OSHA published a directive for inspection of workplaces that create or handle combustible dusts. On March 3, 2008, OSHA reissued this directive “to increase its enforcement activities and to focus on specific industry groups that have experienced either frequent combustible dust incidents or combustible dust incidents with catastrophic consequences.” The new directive increases activities in outreach, training, the creation and dissemination of guidance and educational materials and cooperative ventures, as well as enhancing its enforcement activities. Read more

Changes to the 2013 Edition of NFPA 654

After much anticipation, the new 2013 Edition of NFPA 6541, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing and Handling of Combustible Particulate Solids, has finally been issued. This is one of the key standards utilized for safe handling of combustible solids. Several important updates and additions were incorporated into this edition of the standard, including: Updated definition of a combustible dust, added determination method for a dust flash fire or explosion hazard area, added housekeeping frequency specification and cleaning methods, updated recommendations for separation, segregation, or detachment, updated usage specifics for flexible and rigid intermediate bulk containers, strengthening of included safety management systems (SMSs), and added contractor and subcontractor management system. Read more

Chemical Interaction Matrices

Despite the promulgation of the “PSM Standard” by OSHA in 1992, chemical accidents continue to occur at an alarming rate. As part of the process safety information element of the standard, OSHA requires reactivity data on the chemicals in the process. Part of this reactivity data is a chemical interaction matrix. Several software programs provide simple approaches to generating these interaction charts for common materials using assigned reactive groups. If your process involves materials not included, you are left to determine the reactivity and incompatibilities on your own. This presentation will explain a process for assigning reactive groups using chemical classification and structural analysis. This process can be used for less commonly understood materials such as additives, lubricants, etc. that may come into contact with process chemicals. Read more

Laminar Flame Speeds Data Collection

Regarding vessels and tubes containing combustible gases or dusts, it is important to acquire knowledge on the conditions under which a fuel and oxidizer could undergo explosive reactions. These conditions are strongly dependent on the pressure and temperature. Given a premixed fuel-oxidizer system at room temperature and ambient pressure, the mixture is essentially unreactive. However, if an ignition source is applied locally and the composition of the mixture is within certain limits (the so-called flammability limits), a region of explosive reaction can propagate through the gaseous mixture due to mainly two phenomena: (1) Temperature rises substantially, (2) High concentration of radicals to form. Characterizing potential explosive reactions is one of the main objectives of hazard assessment. Safeguards to be implemented in process equipment, best process conditions, appropriate prevention and/or mitigation measures, are some of the key purposes to be clarified when handling flammable mixtures. This characterization requires knowledge of several parameters that directly influence on the explosive reaction behavior. One of these parameters is the Laminar Flame Speed, which is one of the key factors that define the kinetics of the reaction. The present paper addresses how to characterize fuel-oxidizer explosive reactions, and highlights the importance of the laminar flame speed concept. The main purpose of this study is to provide reliable data regarding laminar flame speeds with the aim to ensure accurate calculations for hazard assessment purposes. Read more

Reactive Chemical Storage

It is a common practice to insulate storage tanks containing reactive chemicals to protect against fire exposure. While this mitigation technique is appropriate for vessels handling non-reactive chemicals, reactive chemicals storage represents a special challenge and must be examined on a case-by-case basis. For certain classes of reactive chemicals, given a sufficiently long hold time, the insulation will always lead to a runaway reaction. If insulation is to be used, special handling is required in order to insure that after the fire is extinguished, the vessel contents do not reach a temperature that causes a runaway within 48 hours. The 48 hours time limit is selected arbitrarily and should be long enough for most installations to empty the tank contents, inject and circulate additional inhibitor into the tank, cool the tank contents, and/or use the vessel contents in the process. Read more

Reactivity Screening Made Easy

During the past decade, large efforts were made by the US chemical and petrochemical industries to implement and maintain effective process safety management (PSM) and responsible care programs. Despite these large investments, incidents continue to occur at an alarming frequency. Many executives of leading companies are trying to understand why. A recent survey conducted by the US Chemical and Safety Hazard Investigation Board (CSB) concluded that reactive chemicals present a significant safety problem for the chemical process industries. Key root causes identified by the CSB survey included technical and management systems failures. This underscores the importance of the need to understand and manage chemical reaction hazards more effectively. We also believe that the “quality” of implementation, change management, and auditing of corporate PSM programs is the culprit. We focus in this short paper on incidents caused by runaway reactions and provide guidance on how to improve the “Quality” of managing chemical reactions hazards through a combination of screening and experimental tools. Read more