Poor design

Entrainment separation is accomplished with inertial separators, which are usually cyclones or impingement separators of various forms. If properly designed, these devices can remove virtually all droplets of the sizes produced in scrubbers. However, reentrainment of liquid can take place in poorly designed or overloaded separators. 

Unbumed Hydrocarbons Various unburned hydrocarbon species may be emitted from hydrocarbon flames. In general, there are two classes of unburned hydrocarbons (1) small molecules that are the intermediate products of combustion (for example, formaldehyde) and (2) larger molecules that are formed by pyro-synthesis in hot, fuel-rich zones within flames, e.g., benzene, toluene, xylene, and various polycyclic aromatic hydrocarbons (PAHs). Many of these species are listed as Hazardous Air Pollutants (HAPs) in Title III of the Clean Air Act Amendment of 1990 and are therefore of particular concern. In a well-adjusted combustion system, emission or HAPs is extremely low (typically, parts per trillion to parts per billion). However, emission of certain HAPs may be of concern in poorly designed or maladjusted systems. 

For example, unsatisfactory equipment design has caused inlet-end erosion due to improper distribution of water in the water box. Poor design and construction practices have caused erosion-corrosion of the tube sheet due to unsatisfactory water distribution or leakage past pass partitions. Deep channels (wire drawing) or worm holes have been observed in tube holes due to leaking tube-to-tube sheet joints. 

As a result of these poorly designed control systems, users experience significant operational problems, including machine and process shutdowns. As with any process plant, the first objective is to achieve reliable production from the FCCU. Only with reliable production will operators start optimizing the unit. Users, therefore, are not using the... 

Another type of utility that is a serious air pollution source is the one that handles the wastes of modem society. An overloaded, poorly designed... 

Blade flutter and rotating stall are problems encountered in the compressor due to poor design or contamination of the blades. Changing blade angles can usually solve the problem however, this adjustment is very... 

Before selecting or sizing a specific control device, a careful evaluation of all aspects of the process and contaminants must be made. Improper terminology can lead to poor design and/or operation of any type of device. A list of contaminant definitions in accordance with the USA Standards Institute includes the following. 

Poor understanding of the reaction chemistry resulting in a poorly designed plant. 

I lii.s case is an example of system-induced error." The poor design of the information display and poor steam valve icccssibility created the conditions for failure. 

Poor design that stored MIC in large tanks... 

Fans with poorly designed or excessively simple straight blades should be replaced with quality fans with lower noise generation. As the accumulation of dirt on impellers often causes imbalance, leading to vibration and... 

In contrast, a case of overfilling, which was the subject of an official report [1], was due to the poor design of complex automatic equipment at a large teirninal for loading gasoline and other hydrocarbons. 

Many accidents, particularly on batch plants, have been due to runaway reactions, that is, reactions that get out of control. The reaction becomes so rapid that the cooling system cannot prevent a rapid rise in temperature, and/or the relief valve or rupture disc cannot prevent a rapid rise in pressure, and the reactor ruptures. Examples are described in the chapter on human error (Sections 3.2.1 e and 3.2.8), although the incidents were really due to poor design, which left traps into which someone ultimately fell. 

Other frequent causes were poor design or use of drains and vents (see index) and freezing of water (see Section 9.1.1). 

An opportimity for error recovery would have been to implement a checking stage by a supervisor or independent worker, since this was a critical maintenance operation. However, this had not been done. Another aspect of the unforgiving environment was the vulnerability of the system to a single human error. The fact that the critical water jacket flow was dependent upon a single pump was a poor design that would have been detected if a hazard identification technique such as a hazard and operability study (HAZOP) had been used to assess the design. 

Inadequate ergonomic design in areas such as control panels and the labeling and placement of valves on the plant can also be regarded as a latent failure because it will increase the probability of active errors. For example, a worker may misread process information from a poorly designed display. Poorly labeled and situated valves can cause the wrong valve to be selected, with possibly disastrous consequences. 

These examples illustrate incidents tliat led to accidents. Ignorance of readings and alanns, poor instructions, lack of proper training, poor design, and ignorance of basic scientific principles lue oHen factors beliind hmnan error. 

System efficiency is influenced by the air plenum chamber and fan housing. Industrial axial flow fans in proper system design will have efficiencies of approximately 75% based on total pressure. Poor designs can run 40%. Speed reducers are about 75% mechanically efficient. 

A poorly designed discharge manifold can cause shock waves and excessive pressure peaks. This manifold should be as short and direct as possible, avoiding any sharps turns. The conventional small atmospheric air chamber, often furnished with pumps, supplies only a moderate cushioning effect. For best results, this air chamber should be supplemented by a large atmospheric air chamber or by a precharged pulsation dampener. 

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