What is a Gas?

Gas is an essential constituent of human life. The air we breathe is a mixture of diverse gases, primarily oxygen and nitrogen. Gas derives from the word chaos (= disorder, confusion). This is because gases are clusters of molecules that move randomly and chaotically, colliding with one another and with everything around them. Gases present in a space blend rapidly, diffusing with great velocity to occupy the smallest available void.

Air Composition

The table gives the composition of air at sea level (as a percentage by volume at a temperature of 15°C and a pressure of 101325 Pa).

Gases can be lighter than, heavier than, or of the same density as air; they can be odorous or odourless, coloured or colourless. The fact that a gas cannot be seen, touched, or smelled in any atmospheric area does not mean that there is no gas in that area. Gases lighter than air tend towards upper areas, whilst gases heavier than air tend towards the floor. A unit volume of any gas, under identical conditions of temperature and pressure, contains the same number of molecules. For this reason, gases are conventionally measured at high concentrations as % volume (%VOL), at low concentrations in ppm (parts per million), or at very low concentrations in ppb (parts per billion). Both in daily life and in industrial fields, the presence and importance of gas are increasing day by day. In industry, gas appears as an “input” in some processes and as an “output” in others. Depending on their structure, gases exhibit flammable-combustible, toxic (poisonous), or inert properties. It is precisely due to these properties that the control, monitoring, and measurement of gas gain equal importance.

Flammable-Combustible Gases

Due to their chemical structure, these gases possess different flash points; when mixed with air, they become explosive and can ignite with any trigger (such as a spark). An explosion is defined as sudden combustion, releasing a high amount of energy instantaneously and causing harm to humans and the environment.

An explosion depends on the mixing ratio of the gas with air. This mixture must be at such an ideal level for an explosion to occur. An extremely high concentration of this mixture does not mean an explosion will occur in the environment. For gases to reach explosive levels in the atmosphere, lower and upper explosion limits exist: - The lowest concentration at which a gas can ignite and explode is referred to as the Lower Explosive Limit (LEL) . - If the gas concentration is below the LEL level, no explosion occurs. The highest concentration at which the gas can explode is referred to as the Upper Explosive Limit (UEL) .

A significant proportion of flammable-combustible gases consist of hydrocarbon compounds; the simplest hydrocarbon compounds are listed as METHANE, ETHANE, PROPANE and BUTANE . Environments where flammable-combustible gases may be present must be systematically monitored with fixed or portable detectors. Multiple flammable-combustible gases may be present simultaneously in the same environment. The detector system must feature a sensor design capable of detecting the LEL level of this potential gas mixture.

Toxic (Poisonous) Gases

A toxic gas is defined as a gas with a broad mechanism of action that can cause harm up to and including death when inhaled, ingested, or absorbed through the skin. These gases can be colourless and odourless (for example, CO), or they can have an extremely strong odour (for example, H₂S). Exposure to toxic gases in work areas is measured on a TWA (Time-Weighted Average) basis. TWA denotes the average concentration to which an employee may be exposed over an 8-hour working period without adverse health effects. However, there is another limit defined for short-term exposures: STEL (Short-Term Exposure Limit). This limit specifies the average concentration to which exposure can occur for a period of 15 minutes without adverse health effects. For certain gases, instantaneous values take precedence; in measuring these gases, TLV-C (Threshold Limit Value - Ceiling) is taken as the baseline. This value specifies the limit that must never be exceeded, even for an instant. TLV, TWA, and STEL values may vary across countries or international bodies.

Air Composition

Certain toxic gases can have fatal effects even at very low concentrations. Therefore, such toxic gases are monitored at ppm or ppb levels. In addition to their toxic properties, some gases can also possess flammable-combustible characteristics. For this reason, gas detectors (and other instruments) to be used in such atmospheres may need to be ex-proof. (For example, Hydrogen)

Inert Gases

Inert gases are components that under normal conditions cause no harm and do not require monitoring. The most common inert gas, as is known, is Nitrogen (N2) gas in our atmosphere. Helium and Argon gases can be cited as examples of other inert gases. However, if inert gases reach concentrations that displace oxygen in the environment, they produce an asphyxiating effect. Therefore, under certain conditions, inert gases must be monitored, measured, and controlled. Oxygen is an essential gas for life. Under normal conditions, 20.9% of the air we breathe consists of Oxygen. When this concentration drops to levels of 16%, a life-threatening condition begins. For this reason, monitoring, measuring, and keeping under control any type of gas that reduces or displaces oxygen concentration is of vital importance. As can be seen, gases, which are indispensable components of human life, also carry the potential to cause harm to human life and the environment; keeping them under control is therefore critical. Keeping gases under control is achievable through monitoring and measurement using accurate and reliable methods. Our recommendations regarding the measurement of gases using accurate and reliable methods will be featured in our next article. Edited by: Hamdi YÜKSEL All text and visual content on our website belong to the authors of www.novel.com.tr. No content on the website may be copied, modified, or utilised in other print or digital media (websites, blogs, magazines, books, etc.) without written permission. Our rights are protected under the provisions of the Law on Intellectual and Artistic Works No. 5846.