Gas Detector / Gas Detection Instrument

For most applications it is relatively easy to determine whether a stationary or a mobile gas detector is more suitable. The stationary gas detectors are mostly used indoors. If a stationary gas detector is to be used in recreation rooms to monitor the indoor air quality by means of the key variable, such as carbon dioxide concentration, gas detectors with traffic light displays are well suited for indicating the measured values. These green, yellow or red signal lamps or notifications on the displays can be easily recognized in offices and classrooms, even from a longer distance. If the indoor air quality deteriorates, additional ventilation can be provided. For the rooms in which urgent ventilation on is not possible or not desired by the user, the stationary gas detectors with analog or switching outputs can automatically trigger mechanical window openers and increase the air exchange rate of the ventilation systems. Alternatively, persons who are in the endangered area can be warned via connected signal lights or acoustic alarm devices. Stationary gas detectors with interfaces to other devices are also used to monitor and control industrial processes. In addition to the analog and switching outputs, the stationary devices can also be equipped with RS485 or USB connection.

Mobile gas detectors with a memory for measurement data often also have an interface that allows the data to be transferred to a PC. Often the USB interface on the mobile gas detector can be used not only to transfer the data but also to charge the internal battery. Since mobile gas detectors are often used for personal protection in hazardous areas, some of the devices have special functions. For example, one of these special functions in the gas detector can record the total exposure of the carrier for the entire shift. This data can be used to evaluate the total concentration of hazardous substances to which the employee was exposed on that day. To enable the person to be protected to concentrate on his or her task and the environment, the devices can be attached to the clothes and also alert by vibration. To ensure reliable operation even under tough operating conditions with mechanical stress, some of these mobile gas detectors are also tested in special drop tests.

It is essential that the measuring range is selected in consideration of the intended use, i.e. in relation to the purpose of the measurement. For example, a gas warning device for carbon dioxide with a measuring range of up to 500 ppm or up to 60,000 ppm can be selected. But not only the upper limit value, but also the lower value must be considered. Not every gas detector can measure from a concentration of 0 ppm. Some sensors for CO2 are designed in such a way that they can only measure and display values above 400 ppm – which corresponds approximately to the natural concentration of carbon dioxide in the outside air. For many applications this limitation is irrelevant. If, however, the lower values are required for special measurements, care must be taken to select a gas detector that can detect these values.

Also the requirements regarding the measuring and display accuracy of the gas detector depend on the application. For the gas detectors for leak detection, which react already far below dangerous concentrations, displays without numerical values are often sufficient. The presence and the intensity of the gas leakage is visually signaled by several indicator bars or LEDs as well as acoustically and haptically. With higher concentrations of the gas, the number of the bars and the frequency of signal tones and vibrations also increase. In indoor areas where the user can react to too high measured values with ventilation, the gas detectors should have both a numerical value display and a clearly recognizable assignment of the value – for example via the traffic light system. In other monitored areas, the gas detectors should be able to store the measured data as a numerical value and, when the threshold values are reached, to control via interfaces the other devices that either ventilate mechanically or sound an alarm. A gas detector for personal protection or for the control of industrial processes must be able to be set with sufficient accuracy to the critical values for the respective gas.

In addition to the visual display of the measured value as a numerical value, gas detectors can have additional visual, acoustic or haptic alarms. A mobile gas detector for personal protection is often equipped with all three types of alarm. Fire departments and rescue services have defined the criteria after several carbon monoxide poisonings during rescue operations in order to protect the emergency services with reasonably used gas detectors. Often such a gas detector used for personal protection is used with two alarm values. The pre-alarm can be set, for example, to allow a stay of 30 minutes without health damage. The main alarm can then signal that the rescuers are only allowed to stay in the affected area for up to 15 minutes or that the area must be left immediately. Some gas detectors have fixed alarm thresholds, while others can be adjusted to the specific conditions of use.

Depending on the environment in which the gas detector is to be used, the appropriate IP classification must be ensured. The IP degree of protection indicates the degree to which an electrical device is protected against water and ingress of foreign bodies or dust due the construction of the housing. The higher the IP classification, the better the gas detector is protected against these influences.

The prerequisite for a fire is the presence of the three conditions: combustible material, oxygen and ignition source. If flammable material and oxygen already form an ignitable mixture, even single ignition sparks can lead to explosions. According to the evaluations of the Gesamtverband der Deutschen Versicherungswirtschaft e. V. (Association of the German Insurance Industry registered association), fire caused 50 percent of the damage among the commercial companies and even 70 percent of the damage – among the industrial ones. For residential buildings, the share was only about 20 percent of the total regulatory expenditure.

During many fires, toxic gases are produced, which are the main cause of death and health damage caused by fire events. In addition to the carbon monoxide released in all incomplete combustions, additional toxic gases are often produced and spread in the surrounding area. For this reason, ABC-reconnaissance vehicles are used in large fires and in fires at commercial and industrial plants. For example, the gas detectors of such a vehicle measured increased levels of ammonia, chlorine and carbon monoxide during a major fire in Hagen in an adjacent street.

A gas detector for flammable gases often does not indicate the concentration of the gas, but how many percent of the lower explosion limit LEL has already been reached. This makes it easier for the user to assess the danger. The lower explosion limit LEL is the minimum concentration above which the flammable gases are ignitable or even self-ignite in the presence of oxygen. Combustion continues automatically from this concentration and leads to an increase in pressure and temperature. There is a particular danger if flammable gases in explosive concentrations are supplied with additional oxygen. This can happen unconsciously, for example by opening a window or door. This can lead to large-area ignition and a sudden increase in pressure. Gas detectors for flammable gases are used to measure in potentially hazardous areas whether an ignitable concentration is present.

The term F-gases stands for fluorine-containing gases, which contribute significantly to global warming. The contribution of these industrially produced gases, which are mostly used as refrigerants or in manufacturing processes, to global warming is much higher than that of carbon dioxide. In order to be able to compare the effects, for each F-gas the global warming potential is given as GWP value – Global Warming Potential. The GWP value indicates as a factor how much more the F-Gas contributes to the greenhouse effect than carbon dioxide. For carbon dioxide the GWP is therefore 1, ammonia has no greenhouse effect, and for propane the GWP is 3. However, for the refrigerant pentafluoroethane (R125) the GWP is 3,500. One kilogram of the released R125 therefore has the same effect on the global warming as 3,500 kg of carbon dioxide. Both the climate-damaging F-gases and the refrigerants or technical gases that can be used as substitutes can be flammable or toxic. If the gas detector is used, attention should be paid to all three hazard possibilities in terms of measuring range and warning threshold.

In January 2015, the European F-Gas Regulation 517/2014 came into force. Its aim is to restrict further emissions of fluorinated greenhouse gases. In addition to bans on use, restrictions on placing on the market and refilling bans for maintenance and repair, this regulation also covers leakage checks and systems for detecting leaks in equipment containing F-gases. A gas warning device with a sensor adapted to the refrigerant is required for leakage checks. Some gas detectors can also detect several groups of common refrigerants with their sensor. This makes them suitable for detecting leaks in the systems with unknown fillings. These gas detectors usually do not provide exact numerical values, but they do show leaks in refrigerant lines and containers even in already contaminated rooms.