Critical Separation

How far apart should the members of the group be? What we really mean is how far apart they are when each is in the centre of their individual strip. This will be Critical Separation. Two searchers are said to be at Critical Separation when an object placed midway between them is on the limit of visibility of both of them (fig. 1).

Critical Separation is found by laying an object on the ground that is similar to that which is being searched for. Two searchers stand on opposite sides of it and circle round it, keeping it just on the limit of visibility. This gives an indication of not only Critical Separation but also the variability of the terrain. If the searchers have done a significant amount of moving in and out as they have circled the object then it is likely that they will need to do a lot of purposeful wandering as they search as seen in fig. 2.

Fig 1. Searchers at Critical Separation - the object is just visible to each of them; it will be approximately midway between them.

Fig 2. Finding Critical Separation - walk around the object so that it just remains visible; the obstructions in the uneven terrain cause the searcher to move inwards.

The factors that affect searcher spacing are:

1. • what you are looking for – if the object is very small or of a colour that is not very easily distinguished from the background then the searchers will be much closer together than they would be if they were searching for a large, brightly coloured object
2. • the terrain you are searching in – any given object will be easier to detect (and therefore the searchers can be further apart) on flat ground with little or no vegetation compared with uneven ground or tall vegetation
3. • the level of visibility – conditions of poor visibility will at the very least cause the searchers to be close together; at worst they will need to use a different tactic

Searching at Critical Separation represents the most efficient use of trained searchers. There is no duplication of effort brought about by adjacent searchers seeing into each other's strips, as would happen if they were too close (fig. 3). Similarly there will be no dead ground between them, as would happen if they were too far apart (fig. 4).

Fig 3. Searchers too close

Fig 4. Searchers too far apart

The style of searching that involves a small group moving relatively quickly is the way that most searching is done in the Initial Response phase. It is often referred to as Initial Response Searching. The emphasis is on speed, and using small groups enables the Search manager to put search resources into as many areas as possible. Only searchers who have been trained to search in this way should be used for this.

In the Initial Response phase the emphasis is on searching possible routes that the missing person may have taken, or particular locations that they might have visited or in which some accident might have happened to them. We are unlikely to be searching areas.

Later in the search, maybe after the first day, speed is likely to become less important. We are now more concerned with thoroughness. This period of time is referred to as the Intermediate Phase of the search. It consists of searching any new routes and locations that have been suggested, and re-searching the routes and locations searched in the Initial Response. There may be some searching of areas taking place. The technique used for this is referred to as ‘line searching’.

Typically this will involve larger groups moving at slower speeds, with more effort having to be expended on group management. They will be spaced at Critical Separation, with the end-searcher half that distance from the feature being used to define the edge of the segment. If the searchers are trained in purposeful wandering then they will use it.

In the Final Phase of the search (several days later) the searchers will most likely be searching only areas, using a line search technique but with the searchers closer together than Critical Separation; the effect of this is explained in Chapter 7. They may well be searching with a constant spacing (sometimes called ‘grid searching’).

The importance of looking for clues should not be overlooked. There might only be one body in the area being searched, but that body will have left many potential clues in getting to its location. Searchers should understand that a clue and the area around it may contain vital information, and therefore should be treated as a scene of crime.

Search Skills are generally transferable, and therefore skills that are acquired in training on hillsides and in forests can be used in other environments, for example urban areas, riverbanks and roadsides.

Our thanks to the Centre for Search Research,  Northumberland, England