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Plainsboro Center, NJ, United States

Prugh R.W.,Chilworth Global
AIChE Annual Meeting, Conference Proceedings | Year: 2011

The "generic" standard for preventing fires and explosions involving combustible dusts is the National Fire Protection Association publication NFPA 654. In this document, fifteen of the requirements are prefaced with the phrase "if an explosion hazard exists", and an additional four requirements are prefaced with the phrase "if a fire hazard exists". An objective of this paper is to show how explosion hazards can be avoided in many dust-handling processes, by welldesigned, well-constructed, and well-maintained systems that involve reliable control of pertinent variables. The handling of combustible dusts can be hazardous to personnel and property, if the fineparticle dust is dispersed in air, at a concentration that is above the Minimum Explosible Concentration [MEC], and if an adequately-energetic ignition source is present within the cloud. The result could be a flash-fire if the cloud is relatively unconfined, or an explosion if the cloud is confined. In the absence of dispersed dust or if the dust-cloud concentration is below the MEC or if there is no energetic ignition source, neither a flash-fire nor an explosion would occur. Strong efforts should be made to minimize ignition sources and to design and/or control operating parameters such that suspended-dust concentrations that exceed the MEC would be unlikely. This paper shows how explosion hazards can be minimized by preventing the accumulation of dust in ducts, by controlling the accumulation of dust on filter media, and by ensuring an adequate flow of air through equipment that otherwise could accumulate dust. Source

Prugh R.W.,Chilworth Global
AIChE Annual Meeting, Conference Proceedings | Year: 2011

The "Process Safety Management" standard of the Occupational Safety and Health Act [OSHA] requires that "The frequency of inspections and tests of process equipment shall be consistent with applicable manufacturers' recommendations and good engineering practices, and more frequently if determined to be necessary by prior operating experience." Guidance concerning inspection and test frequencies is provided in publications of the Center for Chemical Process Safety, and an objective of this presentation is to compile sources for the available data. Objectives of preventive-maintenance and mechanical-integrity programs are to ensure that devices, systems, and equipment will perform satisfactorily during the interval between inspections or tests [I&T]. Thus, "leading indicators" (such as corrosion rates, and detection of incipient failures) are important in establishing appropriate I&T frequencies, rather than "present conditions" (such as hydrostatic tests, and detection of existing failures) or "lagging indicators" (such as historical failure rates). Of critical importance is the recording of "as-found" conditions, prior to repairs, calibrations, or replacements. Suggestions are provided for adjusting inspectionand- test frequencies and intervals, both upward and downward, as based on a "predictivemaintenance" program. Of current interest is the testing of the shut-off devices on blowout preventers at wellheads beneath oil platforms. Typically, the shut-off devices are of a fail-safe design, where loss of air, gas, or hydraulic pressure would cause the valves to close. Frequent testing is required to ensure that emergency shutdown devices [ESD] will function properly when needed to protect personnel and property. Although the ram preventer (pinch device) cannot be tested without destroying the piping, the actuating systems need similar frequent testing. Source

Prugh R.W.,Chilworth Global
11AIChE - 2011 AIChE Spring Meeting and 7th Global Congress on Process Safety, Conference Proceedings | Year: 2011

Equilibrium concentrations of vapor above toxic liquids can be orders of magnitude above the threshold limit value or other vapor-toxicity criteria. Thus, it is important to know the vapor pressure - and, thus, the concentration in air - at the liquid temperature, to determine the toxicity hazard. The infinite point for liquids, e.g., benzene, cyclohexanes, naphthalene, and hexane, can be used to establish an approximate vapor pressure vs. temperature relationship. Through the use of a graph, the approximate vapor pressure that corresponds to room temperature can be determined from one data point. In addition, transposition of the Antoine equation can be used to derive the A, B, and C constants from these two data points, or from three data points (if available), for use in spreadsheet analysis of toxicity hazard versus liquid temperature. Based on the ratio of equilibrium vapor concentration to toxic concentration, the type of breathing protection can be selected. This is an abstract of a paper presented at the 2011 AIChE Spring Meeting & 7th Global Congress on Process Safety (Chicago, IL 3/13-17/2011). Source

Zeeuwen P.,Chilworth Global | Ebadat V.,Chilworth Global
Chemical Engineering | Year: 2011

An introduction to self-heating phenomena and suggestive measures to control this type of ignition source are discussed. Self-heating can arise by one of two different mechanisms, by exothermic (heat releasing) chemical reactions and by exothermic decomposition. Self-heating of solid materials usually results in smoldering, which can set the material on fire or cause dust explosions, particularly when the smoldering material is disturbed and exposed to air. A single test is usually unable to predict self-heating behavior for all different drying and storage conditions. For large-scale storage situations tests are carried out at different scales so that the effect of the size of the bulk material can be assessed. All tests are carried out in temperature- controlled ovens that allow screening tests and isothermal testing. The test provides a useful tool for a quick identification of the self-ignition hazard of materials and should be conducted for materials whose thermal stability characteristics are not known. Source

Umbrajkar S.,Chilworth Global | Rowe S.,Chilworth Global
AIChE Annual Meeting, Conference Proceedings | Year: 2011

Process-safety studies, when conducted just prior to scale-up, can result in the development of processes that may lack inherent safety. The risk associated with scale-up of such processes is high and requires corrective work to mitigate the risk. It is important to understand that process-safety studies do not involve a single reaction calorimetry test or doing a HAZOP or checking the thermal stability of the compounds involved or making sure the reactor has a vent. Safety is the product of all of these activities, and several others, added together. Doing all areas well, and integrating the various outcomes, provides a holistic strategy which is likely to be highly robust. The key to developing safe processes is in having robust procedures which accompany a process from discovery to large-scale production. Critical safety decisions are made at every stage. This article/presentation discusses the overall strategy and outlines the tasks that are necessary to ensure the safety of a process, when they should be performed, and, critically, how the outcomes of the individual tasks should be integrated to maximise their benefit. The scale-up of a chemical process is collectively dependent on a variety of individual groups within a company. Ideally, a multi-disciplinary team should be appointed to be responsible for each new process to be scaled-up (from laboratory scale through to full scale). Various tools available to generate, and then evaluate, data on reactivity and stability will be discussed. The use of the Criticality Class concept to help understand the level of intrinsic process hazard is exemplified. Where the hazard level is significant, changes to the process or conditions can be implemented such that the process at the end of development is inherently safer. Source

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