Multiple occurring event

Another serious distraction to a process operator is the multiple alarm event, where a single event within the process results in iTuuti-ple alarms. When the operator must individually acknowledge each alarm, considerable time can be lost in silencing the obnoxious annunciator before the real problem is addressed. Air-handling systems are especially vulnerable to this, where any fluctuation in pressure (for example, resulting from a blower trip) can cause a number of pressure alarms to occur. Point alarms (high alarms, low alarms, status alarms, etc.) are especially vulnerable to the multiple alarm event. This can be addressed in one of two ways ... 

Two common DNA-binding structures are found in a variety of transcriptional control proteins. The helix-tum-helix motif allows interaction with DNA sequences. The two a-helices are positioned at an angle to each other. One a-helix (the binding helix) contacts the major groove of the DNA molecule. The other a-helix positions the binding helix relative to the DNA. Transcriptional control proteins can have other domains that allow their interaction with other transcription factors these protein-protein interactions allow multiple binding events to occur. Helix-tum-helix proteins are found in both prokaryotic and eukaryotic systems. See Figure 12-17. 

Fio. 5. Example of unobserved multiple substitution events between two distantly related species (I and II). Although three mutations have occurred since the common ancestor, species I and species II show no differences. 

Non-ideal conditions occur, for example, when the rate of (de)hydrogenation is less than that of cracking, so that the rate of olefin desorption will be low relative to (3-scission, leading to multiple cracking events, and lighter products. In this case a higher iso/normal ratio will be observed in the products than in the ideal case, since secondary isomerisation (i.e. of primary cracked products) is now possible. The results of a classical study of ideal vs. non-ideal HC are shown in Fig. 6.3 (cf. also ref. 27). 

Since these have a common cause, they should be considered as simultaneous events for that cause. If two events do not share a common cause, then the probability that they will occur simultaneously is remote and is not usually considered (API RP 521,3.2). Root cause events such as power loss, utility loss, and external fire will often cause multiple other events and hence large relief loads. 

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