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C MARKETING - INSTALLATION
ISSUE 1, JULY 1971
DIALS, AUTOMATIC, No. 30...
Precautions to be Observed when Handling and Storing
This Instruction details the precautions to be observed when handling and storing Dials,
Automatic, No. 30..., which is the illuminated dial used on Telephones No. 712
(Trimphone). It has a standard trigger mechanism (see M0015) but
differs from the standard type of telephone dial in that it has a moulded transparent
finger plate and the dialling characters are illuminated.
The dialling characters are illuminated by a 'Betalight' unit. This consists of a sealed
glass tube having an inner fluorescent coating and containing tritium gas. The
radioactivity of the gas causes the tube coating to glow. The tube is mounted in a recess
in the dial body immediately beneath a translucent number ring. The glow is apparent only
when viewed in the dark.
To minimise the possibility of breakage of the tubes care must be taken when handling the
dials and telephones fitted with them. Replacement of faulty parts should normally be
limited to the dial fingerplate and label protector but the number ring may be changed
after confirming that the 'Betalight' glows (see par. 6).
4. Radiation hazard
The exceedingly small (virtually nil) amount of radiation that penetrates the glass does
not present any radiation hazard even when there area large number of dials present. The
amount of radiation escaping is only a small fraction of that permitted from a luminous
watch. Single breakage's of tubes, even at the rate of one per week, do not constitute a
health hazard because natural ventilation will disperse the released tritium.
To minimise the hazards from multiple breakage's, storage in stores without mechanical
ventilation capable of 25-30 air changes per hour must not exceed 100 tubes (i.e. dials,
or dials plus telephones) per 1000 cubic feet of free space. The number of tubes that may
be stored can be found by subtracting the volume of the available storage space from the
total volume of the store, and dividing the answer by ten. Where the store is divided into
separate rooms, each room should be considered individually. An emergency procedure should
be drawn up locally that can be put into operation in the event of multiple breakage's.
Dials and telephones should not be stored at heights greater than 2 ft. 6 in. and
individual items should always be packaged.
6. Procedures in the event of breakage
A dial which is suspected to have a broken 'Betalight' should be examined in reducing
light conditions. Viewing down an opaque tube of slightly larger diameter than the dial is
satisfactory. Any dials that do not glow should be regarded as broken. If more then four
breakage's should occur simultaneously the incident should be reported to the Radiological
Protection Officer who will advise on and arrange for any monitoring that may be required.
The Radiological Protection Officer is a member of THQ (p&s4.3), London Material
Section, London, N.l. Telephone 01-226 1262 Extn. 347.
(a) Subscribers' premises. In the event of a dial which does not glow being discovered
on a subscriber's premises it should be recovered and returned to the Supplies Divn.
clearly labelled 'Dial No. 30 with suspect tube'.
(b) Breakage's indoors. When breakage's occur, or as soon as they are discovered,
ventilate the affected area. If the number of dials or telephones involved is greater than
four, remove the suspect stock to a well ventilated place, preferably out-of-doors.
Inspect the items and report as detailed above.
(c) Breakage's outdoors. When breakage's occur in the open the radioactive gas will be
(d) Breakage's in transit. Ventilate the vehicle and remove the suspect items, inspect
the items and report as detailed above.
(e) Disposal. The number ring must not be removed from a Dial No. 30 which is suspected
of having a broken tube, such dials must be returned to the Supplies Divn. securely
wrapped and clearly labelled 'Dials No. 30 with suspect tubes', not more than ten dials
being enclosed in the one package. When a larger quantity of faulty dials needs to be
disposed special arrangements should be made with the Radiological Protection Officer.
(f) Cuts from broken 'Betalights'. Fragments of broken tubes can be expected to be
contained within the dial. Although the fragments of glass may retain some radioactivity
any such fragments can be treated as normal refuse. Should a cut from a fragment of
'Betalight' be suffered the incident should be reported to the Radiological Protection
Disposal will be normally the responsibility of the Supplies Divn. where small quantities
(not more than ten tubes) may be treated as normal refuse but larger quantities will be
subject to the advice of the Radiological Protection Officer.
Additional precautions are not necessary to the normal careful handling of equipment to
prevent damage in transit. If the total load of dials and/or telephones should exceed 1000
the Radiological Protection Officer should be consulted regarding certain statutory
Not more than 50 Dials No. 30 should be packaged together in a single container. As the
'Betalight' may be more vulnerable when the dials not mounted in a telephone, a warning
notice should be displayed on the outside of bulk packages of dials: TRITIUM - CONTAINS
RADIOACTIVE GAS EXTERNAL RADIATION BELOW 0.5 MILLIRAD PER HOUR.