Before overhauling its hydrogen production equipment, a chemical plant conducted a hot work analysis. When the safety manager used a combustible gas detector to measure the hydrogen content inside the cryogenic hydrogen production equipment, the instrument showed a value of <4% (in reality, several measurements were between 3.0% and 3.8% H2). At this point, the safety manager approved the hot work. The instant the welding foreman ignited the welding torch, a violent explosion occurred, causing the entire cryogenic hydrogen production equipment to collapse, resulting in seven deaths and eight injuries.
The causes of this serious accident are multifaceted and irrelevant to this article, so they will not be discussed further. However, the above situation demonstrates that the correct understanding and use of gas detection alarms, which involve safety-related hot work analysis, is a topic worthy of discussion. This article will only provide a preliminary discussion on this topic for the reader's reference.
Functions and limitations of gas detectors and alarms
1. Function
Gas detectors are simple and convenient small instruments, available in both pocket-sized and fixed types. They can be fitted with different types of probes (sensors) to measure various types of gases. Due to their small size, high sensitivity, rapid detection, portability, and low cost, they are used in many production departments to detect the concentration of various combustible and toxic gases.
2. Limitations
The application of gas detectors should primarily focus on qualitative and semi-quantitative analysis. If users only require information about the presence of combustible gases (such as hydrogen or oxygen) and their concentration, a gas detector can provide basic, approximate information for reference. However, if users treat the displayed data as precise data, they will be misled, potentially leading to serious consequences. It should be noted that a gas detector is not a gas analysis instrument; the two differ significantly in performance and application, and this distinction should be clearly understood.
The difference between a gas analyzer and a gas detection alarm
1. Differences in instrument structure
Gas detectors and alarms have a relatively simple structure, consisting only of a probe (sensor) and a sensor signal conversion circuit. Gas analyzers, on the other hand, not only have an internal probe (sensor) but also a complete gas path system, which introduces the sample gas into the instrument and then leads it out for venting or recovery.
2. Different detection methods
Gas detectors and alarms detect gases by directly exposing their probes to the air or sample gas environment. Gas analyzers, on the other hand, introduce the gas (sample gas) to be measured into the instrument through a special method for analysis, and then vent it out of the instrument.
3. Different methods of controlling the measurement conditions
The gas detector alarm does not have a part for adjusting and controlling the sample gas process technology conditions, and it does not take into account the environmental conditions where the sample gas exists, and directly performs detection.
The gas analyzer, along with its internal gas path system and external supporting equipment, forms a relatively complete chemical process flow. The gas analyzer internally adjusts and controls the working conditions of the sample gas in all aspects to ensure the normal and stable operation of the sensor, which is the guarantee that the gas analyzer can obtain accurate measurement data.
4. The operational methods for completing the entire measurement process are different.
When using a gas detector alarm, simply place the instrument within the atmosphere to be measured, and it will display a value. In contrast, a gas analyzer requires careful introduction of the sample gas into the instrument, followed by strict adjustments to process conditions such as temperature, pressure, and flow rate. Accurate measurement data can only be obtained after the operator has adjusted the instrument to achieve a stable chemical process. Data obtained before this point is incorrect and must be discarded.
5. The methods for eliminating interfering factors differ during the testing process.
Gas detectors and alarms place sensors directly in the ambient atmosphere for measurement. Their structural design and practical application do not consider factors that might interfere with the measurement, and they lack the capability to eliminate various interfering factors. In contrast, gas analyzers, when designed, selected, and used, must fully consider all internal and external factors affecting the measurement and meticulously eliminate them one by one. Only in this way can the accuracy and reliability of the detection data be ensured. Otherwise, inappropriately ignoring any influencing factor is unacceptable and impermissible for the detection process.
6. Differences in data accuracy
Gas detectors and alarms can only provide qualitative analysis results and relatively rough quantitative analysis data. The data displayed by such instruments cannot withstand scrutiny and cannot be used for error analysis (because "error" can only be discussed when the analytical data deviates from the true value very small). Therefore, they cannot be used as accurate analytical data to determine (determine) important process improvement and adjustment measures. Gas analyzers, on the other hand, are rigorous measuring instruments that can provide highly accurate data when performing quantitative analysis. This data can serve as the basis for improving and enhancing gas production and safety, guiding and conducting production management, quality management, and enterprise management. Furthermore, this data can serve as important evidence in judicial and criminal investigation work, used in lawsuits to determine the boundaries of right and wrong.
