MSA SIRIUS Instruction Manual page 58

8 Performance Specifications
Use of SIRIUS PID for detection of extremely toxic gases:
The system resolution limit of the SIRIUS PID in normal mode (with a new, clean lamp)
is approximately 0.1 ppm isobutylene equivalent. Users must be aware of exposure limit
guidelines, such as TLV, for the target analyte. Do not use the SIRIUS PID Detector if
the exposure limit for the target analyte is below 0.1 ppm.
For any analyte, its exposure limit guideline can be recalculated in terms of equivalent ppm
isobutylene by dividing the exposure limit guideline by the appropriate response factor.
Example: For butadiene (CAS 106-99-0), the recommended threshold limit value (as TWA)
is 1 ppm. Its response factor (10.6 eV lamp) is 0.69. The TLV for butadiene, in terms of
equivalent ppm isobutylene is:
ppm ÷ 0.69 = 1.4 ppm isobutylene equivalent.
The SIRIUS PID Detector has a reproducibility of ±2 ppm (±2000 ppb) or 10%, whichever
is greater (see Table 14). The user must account for this potential variation between the
displayed value and the actual concentration when setting alarms and interpreting readings.
Gases with very high response factors (RF):
The SIRIUS PID is a very versatile solution for monitoring many different gases and vapors.
In addition to the pre-programmed list provided in the SIRIUS instrument, users can deter-
mine response factors for many other compounds (see 4.3). The maximum response factor
value that will be accepted by the SIRIUS instrument is 39.99. Following the procedure in
Chapter 4, if a response factor of greater than 39.99 is experimentally determined, the user
must use the next higher energy lamp (9.6, 10.6, or 11.7 eV) to monitor that compound. If a
response factor of greater than 39.99 is experimentally determined when using the 11.7 eV
lamp, the compound of interest has an ionization potential too high to be detected reliably
using the SIRIUS instrument.
Use the correct bulb when determining the response factor.
Failure to apply the appropriate response factors can result in inaccurate readings.
These additional response factors were determined by MSA Chemists using the SIRIUS
Multigas Detector. The listing consists of response factors for several common industrial
chemicals that are notpreprogrammed into the instrument. Using your IBM compatible PC
with the Data Logging Software and Data Docking Module, you can add a response factor
from this list to the monitor's internal gas table. Consult the Data Logging Software User's
Manual for specific instruction. MSA is continually developing new Response Factors;
contact MSA if your compound of interest is not listed.
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