Field Of Explosion Protection Research Articles

Shear-stiffening porous material with impact-hardening functionality: Application in hydrogen explosion safety protection

In this study, a shear-stiffening composite porous material (PU@CS) was developed using the dipping-drying technique, with polyurethane (PU) as the substrate. PU@CS not only overcomes the cold flow drawbacks of shear-stiffening gel (SSG) but also significantly enhances the mechanical properties of PU (with a one-order-of-magnitude increase in maximum storage modulus). The introduction of multi-walled carbon nanotubes (MWCNTs) overcomes the electrostatic aggregation drawback of PU. Due to its outstanding shear hardening effect, PU@CS exhibits superior explosion-proof compared to PU, and when filled to a length of 50 cm, it achieves complete quenching of hydrogen gas explosion flames, with a maximum explosion overpressure attenuation ratio of 87.2%. This work provides data support for the application of SSG in the field of explosion protection.

Dynamics of the standardization process for explosive atmospheres

This paper presents an overview of the standardization activity in the field of explosive atmospheres both at the national and international level, as well as the evolution of this activity in different areas related to these explosive atmospheres. In the first part of the paper, the aspects regarding explosion risk, explosion prevention and protection, classification of explosive atmospheres, as well as factors influencing explosion protection are briefly presented. In the second part of the paper, the context of standardization at the national level is presented together with the reference institutions in the field of standardization for or in relation to explosive atmospheres. On this occasion, the international institutions that administer the standards that have an impact in the field of regulations for explosive atmospheres at the national level are also presented. In the last part of the paper, the analysis carried out for several representative standards in the field of explosion protection is presented, from the point of view of the significant changes made in the current edition compared to the previous edition.

Comprehensive research method for explosive coal dust

The article briefly analyses the explosion and fire hazard properties of coal dust of different dispersions. It is emphasised that many experts working in the field of explosion protection and industrial safety pay insufficient attention to changes in the properties of the dust when reducing its dispersity. It is suggested to develop a new, complex methodology based on the dispersed composition of coal dust. The authors suggest to put methods of special sample preparation and dispersing of samples in two stages as a basis of the complex methodology. To do research with the help of thermal synchronous analysis of the smaller fractions, the authors propose to regrind the coal fraction obtained after the cone crusher in an analytical mill. To exclude adhesion of particles due to the process of static charges accumulation it is suggested to use impactless sieving machine of Retsch company which allows to take out the accumulated charges of static electricity. The coal dust fractions obtained after sieving were sent for granulometric analysis by a dynamic image processing method in CAMSIRE and by an optical microscopic method using a LEICA DM 4000 with image scope colour processing. A simultaneous thermal analysis was performed selectively for fractions smaller than 1000 μm. This was carried out with an STA 449 F3 and NETZSCH Proteus termal analysis application software. The authors consider that the obtained results allow to conclude that it is further expedient to carry out research work in this direction and will make it possible to develop recommendations aimed at prevention of coal dust aerosol explosions.

Study on the Mechanism of Sparks Generated Mechanical Friction

In the field of explosion protection, measures must be taken to prevent ignition sources due to mechanical friction and impact. One of the most dangerous sources of ignition in methane-air mixtures is sparks, which are easily induced by friction and impact from light metals. In general, sparks and hot surfaces are coexistent in the friction processes of metal contacts. The questions are whether sparks are a truly effective ignition source and whether the nature of materials plays a decisive role in the ignition ability of sparks. Therefore, this research focuses on the temperature of hot surfaces and sparks generated by friction between pure copper, Q235A steel, and TC4 titanium alloy and the grinding wheel. The effect of the relative rotating speed on the friction temperature and friction spark characteristics is investigated. The result indicates that friction sparks are indeed easier to detonate gas than hot surfaces. Moreover, a mathematical model based on the heat transfer theory is used to prove that the sparks induced by friction from TC4 alloys are more hazardous than those induced by friction from copper and Q235A steel. The factors affecting the energy released by sparks are listed in the formula.

Effects of nozzle geometry on the reignition by hot gas jets

ABSTRACTIn this paper, the ignition of a hydrogen–air mixture by a jet of burned hot gas (often termed reignition in the field of explosion protection) is studied in a two-chamber experimental configuration. This experiment allows systematic creation of hot gas jets emerging from a thin, long nozzle and them to impinge into an unburned, cold hydrogen–air mixture, possibly causing (re)ignition. In an extensive parametric study, hot exhaust gas jets originating from different nozzle diameters (0.6 mm–1.2 mm) and lengths (25 mm and 70 mm), as well as different pressure ratios along the nozzle (up to 5.5) were tested for their ability to reignite the hydrogen–air mixture. It was investigated how often reignition occurred within 10 tests under each condition. Dependencies between the occurrence of reignition and the mentioned nozzle and jet parameters were determined. It was found that the outcome (reignition or no reignition) can differ for nominally identical experimental paramete rs, which demonstrates the parametric sensitivity of the process. The statistical frequency of reignition occurrence depends on the nozzle diameter as well as on its length. For pressure ratios above the critical value, reignition occurred more often for the longer nozzle (l = 70 mm) at a given diameter. Some of these findings, notably the dependence on the nozzle length, pose a challenge to conventional models.

Redesign of a soft conductive rubber strip electrode for measurement of surface resistance according to IEC 60079-32-2 within the context of the PTB Ex Proficiency Testing Scheme

To ensure worldwide quality and homogeneity in the field of explosion protection, not only uniform rules in the form of IEC standards but also the active participation in interlaboratory comparisons are necessary. The “PTB Ex Proficiency Testing Scheme” is the first global proficiency testing program of its kind in the field of explosion protection. It serves as proof of competence and provides laboratories with a complete system for their own performance evaluation.In 2015, the program “Electrostatic Charge - Test Round 2015” was launched within the PTB Testing Scheme. The participants of the program performed surface resistance and transferred charge tests according to IEC 60079-0 and IEC 60079-32-2 on various types of test samples. The new standard IEC 60079-32-2 proposes different kinds of electrodes for the user, such as conductive silver paint electrodes, soft conductive rubber strip electrodes on spring-mounted metal tongues or conductive foam strips mounted on an insulating support, depending on the geometry of the sample. These different types of electrodes as well as the construction latitude for each electrode could lead to deviations between the results of different test laboratories due to better or worse electrode contact with the test sample.Therefore, the proficiency team and electrostatic experts at PTB decided to design an accurate and user-friendly electrode which meets the requirements of IEC 60079-32-2. This paper provides information about the electrodes' design as well as the results of comparable measurements.

Incendivity of aluminium bronze in mechanical friction contacts

The occurrence and incendivity of mechanically generated sparks and hot surfaces in friction contacts are presented when using aluminium bronze. These ignition sources must be taken into consideration when using mechanical equipment in explosive atmospheres. Frictional processes can be caused by malfunctions. In the field of explosion protection, bronze is commonly considered to be an alloy with a low tendency to form mechanically generated sparks. This mainly applies to tin bronze. In many industrial applications, bronze alloys are used today which are particularly hard and have a relatively low thermal conductivity. The question arises therefore as to whether the low tendency to form mechanically generated sparks also applies to aluminium bronze. A second question to clarify is how incentive – compared to contacts of stainless steel and mild steel – frictional contacts of aluminium bronze are. The experimental set-up consisted in a friction pin which was pressed onto a rotating friction disc. The temperature development and the spark formation were observed. Subsequently, it was checked whether the potential ignition source had become effective. Furthermore, it was examined as to how far the incendivity of aluminium bronze differs from the incendivity of stainless steel and mild steel. The experiments showed that friction velocities between 1 m/s and 20 m/s and surface pressures between 1 N/mm2 and 40 N/mm2 did not cause any mechanically generated friction sparks. The temperature of the friction pin develops as a function of the mechanical power density applied. In the case of larger power densities, higher maximum temperatures were reached. Furthermore, the time until maximum temperature was reached was significantly longer at lower power densities. For power densities of 2 W/mm2 and 140 W/mm2, maximum temperatures of 165 °C and 872 °C were measured. The ignition tests proved that with friction partners made of aluminium bronze, hydrogen/air mixtures can be ignited. In all experiments, the effective ignition source originated from the hot surface. A power density of at least 10.5 W/mm2 is required for ignition. The ignition threshold of aluminium bronze is about two times higher than the value of homogeneous mild steel (5.5 W/mm2) and four times the value of homogeneous stainless steel (2.8 W/mm2). In ignition tests with ethene, no ignition was generated by friction of aluminium bronze.

Results of the first electrostatic proficiency testing program IEC 60079-0 versus IEC 60079-32-2 and necessary consequences

Laboratories in the field of explosion protection (Ex-testing laboratories) are required to participate in proficiency testing programs in order to fulfill the requirement of performing interlaboratory comparisons. This paper introduces the electrostatic proficiency testing program titled "Electrostatic Charge – Test Round 2015″ as part of the “PTB Ex Proficiency Testing Scheme”, which represents the first comprehensive proficiency testing scheme in explosion protection. More than 50 laboratories all over the world performed surface resistance measurements and transferred charge tests in accordance with IEC 60079-0 (2011) and IEC 60079-32-2 (2015) on various types of test samples.Although both standards use what is essentially the same test setup, there exist several differences between the test procedures, which may lead to different results. The analysis of the participants' results shows that factors such as the type of electrodes, the level of the measuring voltage, the precleaning procedure, the relative humidity and the definition of the threshold limits can have an influence on the outcome of the tests. In this work, the differences between both standards – IEC 60079-0 (2011) and IEC 60079-32-2 (2015) – and the issues associated with using two different procedures to reach the same goal are discussed and illustrated.

The “PTB Ex Proficiency Testing Scheme” - Interlaboratory Comparisons in the Field of Explosion Protection

The requirement of participation in interlaboratory comparisons was not sufficiently fulfilled by laboratories in the field of explosion protection (Ex-testing laboratories) due to a lack of proficiency testing programs. The reasons were the extensive effort, the complexity of the relevant measurands- and characteristics of interest and difficulties with the selection of appropriate test samples.The present paper introduces the PTB Ex Proficiency Testing Scheme as the first comprehensive proficiency testing program in explosive protection. Furthermore, a detailed look into the program “Explosion Pressure” is presented with a discussion about the reasons for differences in the results of the participants. It is shown that the scheme can improve the performance of the participated Ex-testing laboratories which generates additional confidence for the whole community related to the topic explosion protection..