The issue of toxicity alarms for ethylene oxide
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Our company’s ethylene oxide toxicity alarm sets the first level at 1 ppm and the second level at 2 ppm; it gives false alarms frequently (painting, strange odors, as well as other substances such as methanol and ethanol can trigger alerts). Is there any way to solve this problem?
I assume you are using a combustible gas detector that is non-selective, and in that case there is no solution. You can use gas detectors with high selectivity, but the cost can be very high. If the requirement for alarm latency is not strict, an online chromatograph can also be used as a means for alarm detection.
It’s a toxic alarm; we’ve tried different manufacturers’ models and tested them all
The alarm threshold can be increased: alarm at 8 ppm, interlock at 10 ppm, and SIS intervention for shutdown at 20 ppm
The alarm device you have installed there is likely not an alarm device designed for detecting ethylene oxide as a hazardous gas. Actually, the situation is similar to what I have here: toxic gas detectors can give false alarms due to other substances. I’ve tried many different manufacturers, and in the end I chose detectors that are designed to detect specific substances. They are expensive, but the rate of false alarms is low. At the same time, try to minimize painting work in the surrounding area; moreover, when carrying out painting work, protect the instruments and inform the management department.
What standards are 10ppm and 20ppm based on?
Internal control of the unit. The calculation basis is, for example, GB/T50492-2019; the lower explosive limit LEL of flammable gases, the occupational exposure limit OEL, and the health-based concentration IDLH for toxic gases are considered, with the lowest value among these three being adopted. Among them, IDLH is considered only when the instrument range is insufficient. The LEL for ethylene oxide is 3%; according to the specifications, the first-level alarm threshold is set at 25% and the second-level alarm threshold at 50%. Thus, the alarm value should be below 0.75% (7500 ppm), while the interlock value should be below 1.5% (15000 ppm). The OEL for ethylene oxide is 600 ppm; according to the specifications, the first-level alarm threshold is set at 100% and the second-level alarm threshold at 200%, so the alarm value is set below 600 ppm, while the interlock value is set below 1200 ppm. For ethylene oxide, the IDLH value is 22.4/44*298.15/273*1/1*1500 = 834 ppm. According to the standards, the first-level alarm threshold is set at 5% and the second-level alarm threshold at 10%; thus, the alarm value should be below 41 ppm, while the interlock value should be below 83 ppm. All the values calculated above are the most basic settings; a first-level alarm is treated as a high-level alarm, while a second-level alarm is treated as a very high-level alarm, with interlocks being triggered simultaneously. Due to factors such as response time, it is advisable to choose a value that is lower than the calculated value, that is, to include a margin of safety.