From: ajw@squid.mel.dit.CSIRO.AU (Andrew Waugh)
Subject: Re: Torpedos  (was: Incident on Boston (MBTA) Commuter Rail)
Organization: CSIRO, Division of Information Technology, Melbourne
Date: Wed, 23 Dec 92 22:24:41 GMT

In article <1992Dec22.134008.8594@ryn.mro4.dec.com> pierson@empror.enet.dec.com (dave pierson) writes:
>In the UK and possibly elsewhere, sometimes called a "fog signal", and
>some signals were fitted to place and remove the "fog signals" when the
>fog was sufficiently bad.

They were also known (possibly informally) in the UK as 'detonators'.

Traditional UK signalling works on quite different principles to those
used in the USA. While detonators are used to protect obstructions
(such as broken down trains), the most common traditional use was in
'shotting' distant signals at times of fog or snow storm.

When visibility fell too low at a signalbox, the Signalman would
call out the Fog Signalmen. These were usually members of the local
track gang. These worthys then had the dubious pleasure of standing
at the distant signal (and, occasionally, other signals) for hours
on end in a cold dank fog, or worse, in a freezing snowstorm. This
was often at night; after a full days work. Their only consolation was
the overtime payments! Their job was to place detonators on the track
whenever the distant signal was at danger. A train, when passing the
distant, would explode the detonators and inform the Driver that he
was passing a distant signal at danger and so should start slowing down.

Fog Signalmen have generally been replaced by AWS systems.

At some places it was too dangerous for a Fog Signalman to shot signals.
An example would be the inside lines of four track lines. For such
locations detonator placing machines were invented. These had a magazine
full of detonators and an arm which placed a detonator on the rail.
Detonators could be placed and removed from the rail by working a
remote lever. For fogging duties, such detonator machines would be
worked by a Fog Signalman.

As this century wore on, some of the railway companies began equipping
signalboxes with a detonator machine for each main line. The machines
were located whereever convenient (often opposite the signalbox) and
were not associated with any signal. They were for emergency use.
A typical situation where they were used would be if a train was
running through signals, the signalman would operate the machine to
give a warning to the train crew. The machines were operated by levers
in the signalbox. These could either be full sized levers in the
interlocking frame or small levers in a separate frame. They were
painted black (?) with white chevrons. The chevrons pointed up for
the lever controlling detonator placers on the Up line and down for
machines on the Down line. The Railway Inspectorate encouraged
companies to equip their signalboxes with this equipment, but it
wasn't until after the second world war that they became at all common.

Finally, detonator placing machines could be provided to protect
particular danger points. An example would:

------------------------------------------->

-------------------------------------------<
                       \
                        ---o---------------<
                      ------|  +===========
                       |       | (platform)

This part of a station with a two track main line with a platform
a loop line. There is a starting signal at the platform end and
a detonator machine (represented by the 'o') on the loop line
immediately in advance of the signal.

It has been known for a train standing at the platform to start
while the signal was still at danger. This set up an extremely
dangerous situation as a second train could be approaching the station
at speed on the main line. The first train would not have to move
very far past the signal before it fouled the main line.

In such a situation the detonator placer provided a valuable safety
backup as the erring engine would almost immediately explode a
detonator and (hopefully) stop before fouling the main line. Such
a detonator was usually worked by the _point_ lever, not the signal
lever, as the machine was operated by rodding. If the points were
normal for the main line the detonators were on the rail, reverse
for the loop, the detonators were off.

andrew waugh
Newsgroups: rec.railroad