Page 42 - Eric C. Fry - Knots and Ropework

23 This is an acknowledged and perfectly efficient knot, but it can be
dangerous when used by amateurs as a lifel ine. The purpose of
the knot is to provide a quick release by simply tugging the tail
Thief Knot end, whilst the standing part is capable of supporting a load.
It can be used, with a short tail, whenever it is necessary to slip a
orDraw load. But it is more often associated with the fi re service where
its purpose is to provide the means of escape, as a lifeline,
Hitch coupled with the advantage that the rope is retrievable. Should
the buildi ng be higher than ha lf the length of the rope, the
procedure is repeated from one convenient level to the next, until
the operator reaches the grou nd. In this event the hitch is formed
with the bight at the centre of the rope, and both ends hanging
down. The operator, having shinned down the standing part
retrieves his rope by tugging the other fa ll, hence the alternative
name of thief knot.
It is apparent from the illustrations that one fall of the rope will
support a load (the left fall in Fig 6) whilst the other will not and
as the two falls lay side by side. confusion between them, whilst
understandable. could prove fatal.
Note
The danger of confusing the two falls cannot be too highly
stressed. even to professionals much less to amateurs. It was not
long ago that such a confusion resulted in a highly trained and
competent man falling to his death. w ith his rope on top of him.