Explosion Testing Laboratory
In modern industry, process safety is of central importance, especially when dealing with potentially hazardous substances and mixtures.
To minimize risks and ensure maximum safety, it is essential to precisely know the safety-related parameters of these substances.
The parameters available in literature are usually based on standard conditions, which can significantly differ from process conditions and should be critically examined from a safety perspective.
Our PROTEGO® testing laboratory offers the possibility to determine various parameters under non- atmospheric conditions Atmospheric conditions Atmospheric conditions are pressures from 80 kPa till 110 kPa and temperatures from -20°C up to +60°C. , allowing to identify the influence of your individual process conditions (pressure, temperature, oxidizing agents, inert gases, etc.).
The investigation of explosion Explosion Abrupt oxidation or decomposition reaction producing an increase in temperature, pressure, or in both simultaneously. pressure, flammable limits, maximum explosion pressure rise, limiting oxygen concentration, or maximum experimental safe gap under realistic operational conditions provides precise data that contribute to risk minimization and simultaneously avoid costs due to over-engineering.
Maximum experimental safety gap MESG (explosion group)
The assessment of the ignition penetration capability of a substance is determined in accordance with EN ISO/IEC 80079-20-1 in a MESG measuring device Device A device is a pipe component that influences the media flow by opening, closing, or partially shutting off the flow channel or by dividing or mixing the media flow. , and the substance is then classified in one of the explosion groups IIA1, IIA, IIB1, IIB2, IIB3, IIB or IIC based on the experimental results.
The explosion group of a substance is utilised for the purpose of evaluating the suitability of flame arresters Flame Arresters A flame arrester, deflagration arrester, or flame trap is a device or form of construction that will allow free passage of a gas or gaseous mixture but will interrupt or prevent the passage of flame. or devices with the "flameproof enclosure" (Ex d) type of protection for the given substance. In addition to determining the MESG of pure substances, the PROTEGO® testing laboratory also offers the possibility of quantifying the influence of temperature, pressure, inert gases, or oxidizing agents. Possible areas of application could include, for example, determining the necessary inert gas Inert gas Non-flammable gas which will not support combustion and does not react to produce a flammable gas. content to change the explosion group of a specific substance mixture from IIC to IIA, thereby achieving a more cost-efficient plant design.
Lower and upper flammability limit
Various measures from the field of primary explosion protection Explosion protection An explosion protection is a flame arrester that prevents flame propagation into plant sections to be protected during explosions. can be applied to prevent explosive atmospheres from occurring within a plant. One of the most important of these is ensuring that the flammable limits of a substance or mixture are not exceeded or fallen below.
These parameters can be determined at atmospheric pressures in accordance with EN 1839:2017-04 using the tube or bomb method, whereby only the bomb method in accordance with EN 17624:2022 is applicable for elevated pressures. In this method, the fuel-air mixture is fed into an explosion pressure autoclave and ignited there by means of high-voltage discharge, exploding wire, or sliding spark ignition.
Dynamic pressure measurement in the wall can be used to detect whether the criterion for ignition of the mixture (5% or 2% pressure increase relative to the initial pressure) is met or whether the value falls below the limit. The mixture can be produced either by means of a partial pressure process or by complete evaporation of liquid streams and subsequent homogenization with the gas or air stream.
When applying explosion limits Explosion limits Limits of explosion range. to ensure safe process control, it should be noted that the key figures determined in the laboratory are not always directly transferable to the process. This may be due to differing environmental conditions, especially temperature and pressure, which can have a critical influence on the key figures.
Flash point
The so-called “flash point” can be used to assess whether or under which environmental conditions a flammable atmosphere occurs above a liquid. This safety parameter is one of the oldest, having been used as standard for explosion risk assessment since the 19th century.
To determine the flash point, a liquid sample of a defined volume is heated using a constant temperature gradient and tested at specific intervals for the possibility of ignition using a suitable ignition source Ignition source Any source with enough energy to initiate combustion. . The type of ignition source, the volume, and the temperature gradient are defined by the standard used, which means that the values determined can vary within a certain range.
It is important to question whether the standard used is applicable to the substance or mixture of substances being tested to take a conservative approach to safety. The example of acetone-ethylene glycol mixtures in the figure shows, that ISO 13736 deviates significantly to the unsafe side compared to ISO 1523 for mixtures with low proportions of low-boiling components or impurities.
Limiting oxygen concentration
In addition to the explosion limits already mentioned, another important parameter for primary explosion protection is the so-called limiting oxygen concentration. This is the highest oxygen concentration in a fuel-inertgas-air mixture at which no explosion can occur.
The LOC can be determined in accordance with EN 1839:2017-04 using the tube or bomb method, whereby this standard is limited to temperatures up to 200 °C and atmospheric initial pressure. If the LOC is to be determined at elevated initial pressures, this can only be done using the bomb method in reference to EN 17624:2022, which defines the determination of explosion limits at pressures up to 100 bar.
In contrast to the determination of explosion limits, the LOC not only varies the proportion of fuel, but also adds an inert gas. By measuring different compositions in the ternary mixture, triangular diagrams with the respective explosion range are obtained, as shown in the figure.
Auto-ignition temperature
In order to assess whether the heating on the surface of an electrical machine, such as a pump or fan, poses an ignition hazard to the surrounding medium in a potentially explosive atmosphere Explosive atmosphere A mixture of air and flammable substance in the form of gases, vapors, mists or dusts under atmospheric conditions in which, after ignition, spreads to the entire unburned mixture. , both the maximum surface temperature of the device and the ignition temperature Ignition temperature Lowest temperature (of a hot surface) at which ignition of a flammable gas or vapor in a mixture with air or air/inert gas occurs under specified test conditions. of the medium must be known.
The auto-ignition temperature of a substance is the temperature at which it ignites spontaneously on a hot surface in an air atmosphere without additional ignition sources such as electrical sparks.
Various standards can be used for this determination, e.g., ISO-IEC 80079-20-1. According to this standard, the determination is carried out in a borosilicate glass Erlenmeyer flask (V = 200 ml), which is heated in an oven.
The Erlenmeyer flask is heated from a temperature of 80 °C using a constant temperature gradient, and the sample is added in defined volumes and at defined intervals. At a certain surface temperature of the Erlenmeyer flask, the sample ignites. Starting from this temperature, tests are carried out at successively lower temperatures to determine whether ignition still occurs until the temperature at which ignition can be reliably ruled out is reached. Based on this temperature, the sample is classified into one of the temperature classes from T1 to T6.
Maximum explosion pressure and pressure rise of gases and vapors
If the primary and secondary explosion protection measures to prevent explosive atmospheres and effective ignition sources do not provide a sufficient level of protection for a specific application, tertiary explosion protection measures can be used. These measures limit the effects of an explosion to a safe level through design measures. This can primarily be achieved through explosion pressure (shock) resistant construction, pressure relief devices, and decoupling systems.
The maximum explosion pressure (pmax) and the rate of pressure increase (dp/dtmax or KG value) are among the factors relevant for the correct design of these measures. These values, as well as the explosion limits and the oxygen limit concentration, can be determined in a spherical explosion pressure autoclave, in which the substance is presented in gaseous or vaporous form and brought to explosion.
Fig. 1 shows examples of the explosion pressure curves and their first derivatives for hydrogen, ethylene, and methane in air. With regard to the explosion pressure, it is clear that the three substances have relatively similar values, but the corresponding pressure rise rates are very different. It can be seen that hydrogen has by far the highest KG value, which is more than twelve times that of methane.
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