Gas detection
Gas detection (ATEX based)
Gas detection device
If the health and safety of personnel depends on it, equipment measuring the concentration of flammable gases, vapors and oxygen must be applied. It can reduce the hazard by issuing an alarm in time, i.e., before the Lower Explosion Limit (LEL) is reached. Gas detectors can also be used to activate fire extinguishing systems or to initiate an evacuation.
A properly functioning gas detector is the result of the correct choice of equipment, correct installation and use, timely calibration and proper maintenance. A solid knowledge of the behavior of the flammable substances present is necessary to make a good choice.
How to choose gas detection equipment?
The following characteristics are important when selecting equipment suitable for the environment:
- Temperature and pressure when the gas is released;
- Sensitivity of the detector to dirt or condensation;
- Sensitivity to "poisoning" (some detectors will react so violently to certain chemicals they do not performwell after exposure).
An additional and life-threatening hazard is the toxicity of many flammable gases and liquids. These gases and vapors are dangerous even at very low concentrations, often much lower than the minimum explosion limit. When using gas detection equipment to detect toxic gases, additional safety measures in the form of personal protective equipment are required.
Portable gas detectors are often equipped with more than one measuring head, e.g., for measuring toxic gases as well as oxygen concentration. A small reduction in oxygen concentration may indicate the presence of toxic gases or vapors that may not (yet) be detected by the gas detection heads at hand.
Use of portable and transportable gas detection equipment
For most daily work situations, the READ & RUN method is ideally suited. This method entails the following:
- In a clean environment, check the gas detector for proper operation;
- In the zone:
- take measurements at various locations;
- take into account the nature of the gas (lighter / heavier than air);
- as soon as the reading indicates 10% LEL or more (READ) leave the workplace immediately following the instructions in the work permit (RUN);
- notify the responsible person / manager.
Gas concentration checks during operation in a zoned area:
- zone 0: eliminate source of danger and continuous monitoring.
- zone 1: continuous monitoring;
- zone 2: regular monitoring (regular = before work starts and at least every 4 hours,preferably more often).
Basic rules for working in a zoned area
A number of basic rules apply to work in zoned areas. For example, it must be ensured before work starts:
- that no explosive atmosphere is present or likely to occur;
- that no sources of ignition are present or likely to form.
As long as the gas concentration is < 10% LEL, work may be carried out as if the zone were a safe area.
If the gas concentration is > 10% LEL, work may not start or must be stopped.
Two further remarks concerning the use of gas detection equipment:
- If gas is released from an active sourceof hazard, its temperature must be taken into account when measuring. For example, methane is a gas lighter than air. If the released gas is colder than the surrounding air, it will still linger for some time for the methane must first heat up before Heating up takes energy and, depending on the temperature difference between the methane and the air, this can take some time.
- Substances with a relatively high flash point such as diesel oil will produce little vapor after a cold night. This is because the temperature of the oil is low at the time. Gas measurements taken early in the morning will show little or no gas.
When the storage tank heats up during the day, more vapor will be emitted. At a sufficiently high temperature (the flash point) an explosive mixture may form. More often than not this change in process conditions goes unnoticed, becoming a danger to work safety in such an environment.
