Toxic Gas Detector Time Delay

Question

Toxic Gas Detector Time Delay

hammy1554 (Chemical)

(OP)

24 Dec 20 07:51

Hello Friends,

We have Ethylene Oxide EO toxic gas detectors (GDT)in side plant. These is deluge activation linked to these EO Toxic gas detectors. Once these gas detectors 10 ppm (2 time of STEL) value it will activate Deluge system.

EO detectors have inherent cross sensitivity issue and we are facing false activation of deluge.

Is there any possible solution to avoid this?

We are intended to put time delay for 1 min or 2 min, if 10 PPM Value stay for more than 1 or 2 min then deluge to activate.

or is it safe to raise the GDT Deluge activate value to 50 ppm?

Please share your experience.

EmmanuelTop (Chemical) · Answer 1 · 2021-01-01 09:31:13

STEL refers to average concentration of 5ppm over time period of 15 minutes, hence you should not have a single detector triggering deluge at any instantaneous value of EtO concentration. Why not use 5ppm over 1 minute period?

What is typically used is to employ signals from two or more detectors in order to initiate executive action. This depends on how the detectors are positioned inside your plant and what is their coverage area. If you depend on a single EtO detector in any given area, you cannot use this approach.

There is no such thing as "common sense" - Apollo RCA

hammy1554 (Chemical) · Answer 2 · 2021-01-07 05:45:46

Issue is false activation, even if we set it at 5 ppm over 1 ppm i will do false activation of deluge. we want to avoid it.
One more issue with the detectors that once they detect a value of 10 or 12 ppm of EtO, it will not go back to original within a min, some time in 90 Sec.

So if we put 1 min time delay for 5 ppm, it still can have activation.

georgeverghese (Chemical) · Answer 3 · 2021-01-10 23:36:55

Activating deluge at STEL seems too conservative. Usually, we only elect to instruct operators to safely stop work and seek egress when concentrations reach STEL. Emergency escape at some higher level than STEL.
What are the other physiological effects on humans of EtO at high concentrations from which we can choose a more reasonable level for deluge activation ? What happens at the suggested 50ppmv ?

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Toxic Gas Detector Time Delay