Negative tree

There are two basic types of analytical tree. The positive tree, or objective tree, which is developed to ensure that a system works properly, and the negative tree, or fault tree, which is generally used for troubleshooting and to investigate system failures (Fig. 10-2). 

These same positive trees are very useful feeder documents for many types of hazard analysis. For example, the item layout for failure mode and effects analysis worksheets can be taken directly from the positive tree for the project. Positive trees can easily be converted into negative trees for troubleshooting or accident analysis. 

The management oversight and risk tree (MORT) chart is a large, complex, negative tree (see Chapter 18). Even though the project evaluation tree (PET) is depicted as a positive tree, it is mentally converted and used as a fault tree for accident analysis applications (see Chapter 16). 

Construct an analytical tree. The tree can be on any subject and either a positive tree or a negative tree. Include at least four tiers in its longest branch, not including the top event as a tier. 

The fault tree (Figure 7.4-1) has "Pre.ssure Tank Rupture" as the top event (gate G1). This may result from random failure of the tank under load (BEl), OR the gate G2, "Tank ruptures due to overpressure" which is made of BE6 "Relief valve fails to open" AND G3, "Pump motor operates too long." This is made of BE2, "Timer contacts fail to open," AND G4, "Negative feedback loop inactive" which is composed of BE3, "Pressure gauge stuck," OR BE4, "Operator fails to open switch," OR "BE5, "Switch fails to open,"... 

Harz-alkohol, m. resin alcohol, -austauscher, m. ion-exchange resin, -baum, m. pitch tree (applied to various conifers), -bildung, /. resin (or rosin) formation, (of gasoline) giim-ming. -brei, m. a viscous material trapped in the pores of a synthetic plastic, resin magma, -cerat, n. Pharm.) rosin cerate, -elektrizi-tat, /. resinous (negative) eleetricity. 

Evaporation ponds are often viewed negatively, particularly due to potential salinisation of local land, unpleasant odours and aesthetic problems (Christen et al. 1999). The siting and design of an evaporation pond must then take these factors into account. The planting of trees around the perimeter of a disposal basin has been suggested as a way to increase social acceptance. The pond site should also include a bulfer zone to position the pond an appropriate distance away from residential and commercial areas, schools, hospitals and other public areas (Jolly et al. 2000 Christen et al. 1999). 

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