ADM, HBOT & Sub Aspida
User Manual
Int. Approved
Document ref: PSA-811-14
June 2017
Page 22 of 43
Copyright © 2017 Analox Ltd. All Rights Reserved.
Commercial in Confidence
5.16
Panic alarm
In cases where a worker is in distress and still conscious, it is possible to activate the ultra-loud siren
manually. To activate the panic alarm, press and hold the
button for a minimum of 1 second.
5.17
Time-weighted average (TWA) monitoring of carbon dioxide
Carbon dioxide is toxic to the human body as concentrations increase. Short term exposure to the gas
can be potentially lethal. Longer term exposure to more moderate levels of carbon dioxide can also be
detrimental to health, so health and safety bodies such as UK HSE define occupational exposure levels
(OEL) for the gas. These OELs provide a recommended safe exposure to carbon dioxide whilst under
working conditions. The occupational exposure levels are based on a calculated time-weighted average
(TWA) level of carbon dioxide in any one 24 hour period. The TWA calculation is based on average
carbon dioxide levels weighted to an assumed standard 8-hour daily working shift.
The Analox
Aspida
has a facility which automatically calculates a TWA value on a per-user basis. When
a user powers on the device and selects a user ID, the Analox
Aspida
begins calculating and
continuously updating that user’s own TWA. The
device also takes into account any historic data from
the last 24 hours which is relevant to the selected user. TWA data is logged alongside the actual gas
readings in the internal data log.
NOTE:
If no users IDs are registered to the device, the TWA values will all be attributed to a default
user.
An alarm feature is provided which will warn of a high TWA exposure to carbon dioxide. In addition to
the normal 3 available gas alarms per sensor, carbon dioxide sensors have a 4
th
alarm (priority 4) which
is triggered when the calculated TWA value exceeds the TWA set-point. This alarm is set by default to
the UK HSE recommended OEL for carbon dioxide of 5000ppm (0.5%). When this alarm is triggered,
the red indicators, vibration and horn warnings will activate as with other gas alarms. In the case of a
TWA alarm, a TWA symbol will be shown below the carbon dioxide reading on the display, as shown
below. The TWA alarm is the lowest priority alarm and as such will be over-ridden by any gas alarms
triggered by a short term increase in carbon dioxide levels.
Figure 7 - The main gas display showing that to user has exceeded their TWA
exposure to carbon dioxide
As with the standard gas alarms, the TWA alarm can also be fully configured using the
Aspida
configuration software.
