Malfunctions

An extremely important safety issue with respect to ah. wood product manufacturing processes is personal worker safety. Ah of the processes use much moving machinery, usuahy including many saws or knives. Workers must continuahy remember the inherent dangers these machines involve as weh as other possible dangerous situations which could result from malfunctions or other errors. In addition, most processes are more or less dusty and noisy. Most employers require use of safety glasses and many require hearing protection, safety shoes, and hardhats as weh as other kinds of protection needed for Specific jobs. 

Whenever unvented combustion occurs iadoors or when venting systems attached to combustion units malfunction, a variety of combustion products win be released to the iadoor environment. Iadoor combustioa units include nonelectric stoves and ovens, furnaces, hot water heaters, space heaters, and wood-burning fireplaces or stoves. Products of combustion include CO, NO, NO2, fine particles, aldehydes, polynuclear aromatics, and other organic compounds. Especially dangerous sources are unvented gas and kerosene [8008-20-6] space heaters which discharge pollutants directly into the living space. The best way to prevent the accumulation of combustion products indoors is to make sure all units are properly vented and properly maintained. 

Absence of ignition peaks or reinforcing pressure waves Minimum gun smoke, flash, and blast pressure Detonation-free in event of malfunction... 

Volatile acids, reported as acetic acid, are the most important operational parameter. In a weU-operating digestion process, the value should be <1 g/L (3.8 g/gal). A value >6 g/L (23 g/gal) indicates malfunctioning optimum pH is 6.8—7.2, and a pH <6.8 indicates excessive volatile acid production. Formerly, lime was added to the digester contents if the pH showed an undesirable drop. However, the reduction in pH indicated a change in organism that could not be remedied with lime (2). 

Ingestion of large amounts of trichloroethylene may cause Hver damage, kidney malfunction, cardiac arrhythmia, and coma (38) vomiting should not be induced, but medical attention should be obtained immediately. 

Considerable effort has been directed to determining the causes of connection failutes and to learning how to minimize the likelihood of occurrence. Acceptable failute rates range from <1 in 10 operating hours for contacts in air-frame (31) electrical systems and in some telecommunications equipment, to 100—1000 in 10 operating hours in instmments, to even larger rates for contacts in many consumer products. A failute is defined as exceedance of contact resistance, which can be as Httle as twice the initial contact resistance, that causes circuit malfunction. The required lifetimes of connectors may be >20 yr, although most required appHcation times ate shorter (see Materials reliability). 

Technical Support Document Revisions to the Malfunction and Diagnostic System Requirements Applicable to 1994 and later New California Passanger Cars, Eight-Duty Trucks, andMedium Duty Vehicles with Feedback Fuel Control Systems (OBD-II), California Air Resources Board, Sacramento, Sept. 14,1989. 

In this example, reactor temperature and coolant malfunction are variables, and high and estabUshed are values. Variables can take symboHc or continuous values. For example, the rule above can alternatively be stated as ... 

Then the certainty of the conclusion, namely "coolant malfunction is estabhshed" is computed as follows ... 

The reactor temperature is required because a high reactor temperature may be indicative of a possible coolant malfunction, which is the hypothesis currendy under consideration in Rule 102. The knowledge for this rule was obtained from Jane Q. Expert."... 

To illustrate the power of the object-oriented style of representation, consider the reactor diagnosis example used eadier in the discussion of rules. Assume that there are several reactors, R-101, R-102, etc, each served by a common cooling system. Relating coolant malfunctions to the temperature in each reactor would need multiple rules, or rules with multiple disjunctions. Instead, if rules are used in combination with the object representation described above, a single general rule can be written to cover all the specific instances, as follows. 

In continuous processes where automatic feedback control has been implemented, the feedback mechanism theoretically ensures that product quality is at or near the set point regardless of process disturbances. This, of course, requires that an appropriate manipulated variable has been identified for adjusting tne product quality. However, even under feedback control, there may be daily variations of product quahty because of disturbances or equipment or instrument malfunctions. These occurrences can be analyzed using the concepts of statistical quahty control. 

Although digital control technology was first apphed to process control in 1959, the total dependence of the early centralized architectures on a single computer for all control and operator interface functions resulted in complex systems with dubious rehability. Adding a second processor increased both the complexity and the cost. Consequently, many installations provided analog backup systems to protect against a computer malfunction. 

For example, in rotary vacuum dryers it is possible to prevent the formation of explosible dust-air mixtures by setting and monitoring a certain partial vacuum (negative pressure). This pressure value must be determined by experiment for each type of dust. With pressures of less than O.I bar, in general, hazardous effects of dust explosions need not be anticipated. If the vacuum system malfunctions, the partial vacuum must be released by inert gas and the instaUation shut down. 

Gans, M., Systematize Troubleshooting Techniques, Chemical Engineeiing Piogiess, April 1991, 25-29. (Equipment malfunction examples)... 

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