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A conveyor system is a fast and efficient mechanical handling apparatus for automatically transporting loads and materials within an area. A conveyor system may use a belt, wheels, rollers, or a chain to transport objects. A mercantile occupancy is typically a building or structure open to the public displaying and selling goods or merchandise. Because mercantile occupancies normally involve the display and sale of large quantities of combustible goods, the potential fire hazard in these occupancies can be relatively significant. Most mercantile occupancies require an automatic fire sprinkler system to achieve a reasonable level of fire and life safety. Small quantities of flammable liquids are common and are permitted in mercantile occupancies. Larger quantities require a permit and may change the occupancy to a high-hazard classification.
Other Hazardous Materials Mercantile occupancies frequently contain, are liquefied petroleum gas (LPG), pesticides, swimming pool chemicals, and aerosols. The size and type of LPG containers limit the number allowed. Other fire code provisions may apply to toxic materials and oxidizing agents. Compatibility can be a concern with strong oxidizing pool chemicals not stored or displayed with flammable or combustible liquids.
A belt conveyor is widely used in mining, metallurgy, coal and other industries. It can be used to transfer bulk materials or materials into pieces. According to different transferring requirements, the transferring system can be of only one belt conveyor or consist of several belt conveyors or combined with other transferring equipment. The belt conveyor can be installed horizontally or aslope to meet the needs of different transferring requirements.
The overall design concepts for surface and underground conveyors are not significantly different. However, underground conveyors require specific consideration with regard to logistics and constructability, together with other considerations such as access and maintainability.
Considering the limited space underground and naturally dusty environment, even with a high-performance dust collection and ventilation system, special attention must be paid to the maintainability of the components, even to changing out a complete conveyor belt after 10+ years of operation.
Another aspect of the conceptual layout of an underground-to-surface conveyor system is the aim of limiting underground transfer points. This leads to single-flight conveyors with maximum feasible lengths and lifts, and thanks to the recent developments in increased belt strength and gearless drive design undergroun
All belts used in the research were ignited by the gas flame, as evidenced by a marked increase in the volume of flame at the burners. Data in tables 2 and 3 show that preheating had no significant effect on belt ignition; ignition occurred only after flame was applied to a belt. Table 2 gives the time between the application of the gas flame and ignition. The average time was 45 seconds, ranging from 10 to 250 seconds for P-O and N-CR belts, respectively. Ventilating conditions had a highly significant effect on ignition; the time decreased with a decrease in air velocity- The type of belt material had a significant effect on ignition. The time required to ignite neoprene was greater than that for the other materials; the least time was required for polyvinyl chloride. An ignition source, type of carcass, and the use of single or parallel belts had no significant effect on the time for ignition.
Table 1:
Table 2:
All belts used in the research ignited. Following ignition, the flame either propagated the full length of the specimen (propagation) or died out within about 2-½ feet from the ignition zone (no propagation).
Data in table 6 are the average flame velocities along the belt. Data for the V2 and V5 ventilation conditions show that flame velocity was significantly greater on rubber than on neoprene or polyvinyl chloride belts. No significant difference is observed between flame velocities on neoprene and polyvinyl chloride materials.
A significantly higher flame velocity developed on belts with an impregnated nylon carcass than on the cotton-rayon carcass belts. Flame velocities were generally higher in trials with preheating (ignition source S1) than without; however, the differences were not statistically significant. Significant differences in flame velocities were not observed between the V2 and V5 ventilation or single-parallel belt configurations.
Table 6:
Temperatures taken in the air 1/8-inch above and the belt 30 seconds before the flame arrived were 4.4°C to 51.7°C above ambient (table 7). These temperatures are considerably below those required to cause the decomposition of conveyor belting. Data in table 8 show that the quantity of gaseous products liberated in laboratory tests becomes appreciable only at a temperature of 260°C and higher. Therefore, it may be assumed that little or no decomposition of the belt occurred ahead of the flame.
Table 7:
The extinguishing agents and techniques studied were evaluated based on the time required to extinguish burning on both the top and bottom belts. A sprinkler system between belts and high-expansion foam was the only effective technique of those tried (table 9). Although water from overhead sprinklers, solid streams, sprays, and fog extinguished the burning on the top belt, smoke and heat prevented firefighters from approaching beyond the front of the conveyor to attack the fire on the burning bottom belt. Potassium bicarbonate applied by rock-dust distributor and by hand-extinguishers quenched flame within 5 feet of the point of application but failed to quench burning downwind. The time for sprinkler systems located between the belts to extinguish burning appears to depend on the spacing between sprays and the rate of flame propagation. For the rubber (R-CR) belt used in these tests, flame propagated at an average rate of 2 fpm in an air velocity of 200 fpm in the test entry of the Experimental Coal Mine.
Table 9:
Tests-covered belts are made of several layers of materials, including fibres, fabrics, most often plastics, i.e., thermoplastic polyurethane (TPU), polyamide (PA) and acrylonitrile butadiene rubber (NBR), and in one case, LL2 natural leather.
Six types of commercial belts, NBR/PA fabric/PA film/PA6/soft NBR (abbreviation XH),
NBR/TPU/PES fabric/TPU/NBR (abbreviation TLA), thermoplastic connection (abbreviation TC),
NBR/PA fabric/PA film/PA fabric/NBR (abbreviation SG), and NBR/PA film/special fabric (abbreviation KSG), serving both the drive and transport functions were used for the tests, including five manufactured by NITTA Co. and one of their leather/PA/leather (abbreviation LL2).
Table 1:
Markings and construction of the tested flat multilayer belts
Figure 1:
Optical light microscopy images of the internal structure of the flat belts: (a) XH, (b) TLA, (c) TC, (d) SG, (e) LL2, and (f) KSG.
The following symbols are used in Table 1: NBR—acrylonitrile butadiene rubber, PA fabric— polyamide fabric, PA film—polyamide film, PES—polyester cord, TPU—polyurethane, PA6— polyamide 6.
Table 1-a lists the XH 500-4 belt type (extra high top cower), which consists of four layers. The top and bottom layers are acrylonitrile butadiene rubber (NBR), and the middle layers are polyamide film (PA) and polyamide fabric (PAFab). This belt, like the previously described KSG belt, is characterized by high flexibility and excellent abrasion resistance and can work under conditions from -20 to 80 °C in printing houses.
Next, the TLA 30E 30 belt type (Table 1-b) was made of multilayer polymeric materials, i.e., the upper and bottom layers are acrylonitrile butadiene rubber (NBR), and the middle layers are made of polyurethane (TPU) and polyester fibre (PES). The TLA belt can be used in the tangential machine for textiles, where at operating temperatures ranging from 0 to 60 °C, it has high abrasion resistance and a high friction coefficient and is capable of handling very heavy loads.
The TC 950 belt (thermoplastic connection) (Table 1-c) was made of polyurethane layers. The lower black layer has a rough structure, and the upper green layer has a smooth structure. The black surface is the running side of the belt, and the upper side can be used for transportation, e.g., in the textile industry. Such bands are used in drives characterized by a high speed of movement, and due to the construction, limited access to the belt. The operating temperature of the belt ranges from − 20 to 60 °C, its linear speed reaches 40 m/s, and because of considerable tensile stretch, it can be placed on pulleys without a tensioner. These belts are used in printing and textile industries in drives without the possibility of using pretension.
The SG 250 flat belt (Table 1-d) was made of several layers of NBR/PA fabric/PA film/NBR. It is characterized by the easy assembly, a long service life, high flexibility, quiet running, and an easy connection process. This belt can be used in the temperature range from − 20 to 80 °C; it shows high flexibility and optimal elongation during operation and can be used on smalldiameter pulleys (from 35 mm). These belts are mainly used in printing, paper processing, packaging machine, parcel and letter sorting, and light transport applications.
The LL2 flat belt (Leder Leder) is made of three alternating layers of leather and polyamide 6 (PA6), as shown in Table 1-e. Such bands are used in multi-shaft drives in a contaminated working environment; they are characterized by good resistance to variable loads, and they perform the function of overload couplings. These belts are characterized by a brief permanent slip, good cooperation with pulleys (the pulley does not damage the belt), and antistatic properties, and are designed to work in the temperature range from − 20 to + 100 °C. The closed belt was obtained by grinding its ends at an angle and heat sealing at 100–120 °C for 15 min. These types of belts are used in mills, chippers, machines, and devices for wood processing.
Table 1-f shows that the KSG belt, which consists of three layers of NBR/PA film/special fabric and shows excellent abrasion resistance, high efficiency, and flexibility, is long-lasting and maintenance-free. At the same time, the band is characterized by high resistance to oils, water and electrification while maintaining an operating temperature range from − 20 to 80 °C. The KSG belt is used in printing houses (folder gluers) in the production of packaging.
As a result of the research, the concentrations of CO gases released during the thermal decomposition and combustion of six samples of conveyor belts or flat drive belts were determined and are illustrated as a function of time in Figure 3.
Figure 3:
Toxic gas concentrations during the thermal decomposition and combustion of the flat drive belts; detail shows a smaller measuring range from 0 to 2000 ppm.
Figure 3 shows that in the case of the tested belts, the emissions of 2 to 4 toxic compounds, such as CO, CO2, HCN, NO, SO2 and HBr, were recorded. It was found that the most frequently emitted gases during combustion were CO and CO2 for all tested belts, followed by HCN in 3 belts, such as XH-500, TC, SG 250, and SO2 in the case of the XH and LL2 belts. The emission of HBr compounds was only recorded in the SG 250 belt. Moreover, no emissions of NO2, NO, HCl, or HF compounds were recorded for the tested belts, as was the case with V-belts, the results of which are described in10. The number and type of toxins released during the burning of the belts are summarized in Table 2.
Table 2:
The type and number of toxins emitted during the combustion of the tested samples.
Belt samples |
XH 500-4 |
TLA-30 |
TC 950 |
SG250 |
LL2 |
KSG |
Type of toxins emitted |
CO, CO2, SO2, HCN |
CO, CO2 |
CO, CO2, HCN |
CO, CO2, HCN, HBr |
CO, CO2, SO2, |
CO, CO2 |
Emitted |
4 |
2 |
3 |
4 |
3 |
2 |
It should be stated that the XH 500-4 and SG 250 belts emit the most toxic substances into the atmosphere during combustion; hence, they pose a serious threat to human health and the environment.
Figures 4, 5, 6, 7 and 8 show the instantaneous emission values of selected toxic gases depending on the type of belt material.
Figure 4:
Figure 5:
Figure 6:
Figure 7:
Figure 8:
SO2 concentration as a function of time during thermal decomposition and combustion of the tested belt samples with the indication of permissible values (Table 2).
Additionally, Table 3 indicates the concentration limits of the products of the thermal decomposition and combustion of the tested materials.
Table 3:
Concentration limits of the thermal decomposition products.
The LC50 parameter indicates the lethal concentration, i.e., the concentration of the substance at which 50% of the exposed organisms die during exposure or in a specified period after exposure. The LC3050i is the concentration that causes 50% of the population to die after 30 min of exposure, and IC50 is the inhibitory concentration that slows down the biological and biochemical functions of organisms by 50%. Under real fire conditions, the mass of a burned belt is much greater than during the test, and the combustion process takes longer. For such conditions, the concentration limits for products of thermal decomposition and combustion of materials are used. The results showed that the CO (Fig. 4), CO2 (Fig. 5), and HCN (Fig. 6) emissions during the thermal decomposition and combustion of the tested samples significantly exceeded all permissible values.
Based on the research, it was found that the HBr emission (Fig. 7) did not exceed the permissible values, and in the case of SO2 emissions (Fig. 8), the permissible values LC3050i and IC50 were exceeded during thermal decomposition and combustion of the samples of materials 1 and 5. However, the LC50 permissible value was only exceeded in the case of the SG belt.
Knowledge of the chemical composition and concentrations of chemical compounds emitted during the combustion of conveyor belts is important for the development of fire protection systems. Research teams developing conveyor fire protection systems are based on three basic types of measurement systems: temperature measurements, smoke measurements and air chemical composition measurements. Integrated systems that use all three control methods are the modern trend in conveyor fire protection systems. The quick detection of the initial phase of fire is possible by using sensors along the route of the conveyor belt. In exemplary systems designed to control conveyor belts made of rubber belts, the detection systems are equipped with sensors of carbon monoxide (CO), hydrogen cyanide (HCN), smoke and temperature or are extended with sulphur dioxide (SO2) sensors. Generally, the results show that classic conveyor belts (based on rubber) are characterized by the following emissions in the case of a fire: smoke, hydrocyanides (HCN), hydrochlorides (HCl), sulphur dioxide (SO2) and carbon monoxide CO.
The results showed that under such conditions, modern conveyor belts may additionally emit carbon dioxide (CO2), sulphur dioxide (SO2) and hydrogen bromides (HBr). In the tested belts, HCl emissions were not noted. Multi-concentration gas detection to detect a fire is beneficial, especially in complex working conditions resulting from the type of transported product. Production areas can be contaminated with a variety of chemical emissions. For example, during the transport of coal and biomass, emissions of carbon monoxide (CO) and hydrocarbons (HC) are widespread. This consequence is due to the phenomena occurring in these materials, e.g., gasification (CO and H2 emission), rot (CO emission) and fermentation (emission of H2, CH4 and complex hydrocarbons).
https://www.911metallurgist.com/fire–hazard–conveyor–belts/#Belt–Ignition https://www.nature.com/articles/s41598–021–87634–9 https://www.fairfaxcounty.gov/fire–ems/fire–marshal/mercantile–occupancy–guideline
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