Abstract
Aim: The paper presents a comparative analysis of parameters for ignitability, flammability and thermal stability for each of the selected types of flour. The tests were performed using food products available on the market and used in the catering and food industry as well as in households, i.e. chickpea, wheat, oat, rice and maize flour. Experimental research demonstrated that the combustibility of flour depends on the type of the plant from which it is made and the thickness of the dust layer.
Introduction: The hazard caused by an explosion of food dusts may be present not only under normal operating conditions of appliances or during technological processes, but primarily during the faulty work of devices or system malfunctions. Explosive mixtures of dust and air may be formed during the transport or storage of raw materials, such as cereals, sugar or flour. In order to ensure the appropriate design and selection of suitable appliances, equipment of mills, elevators and other facilities in which ground grain products are produced, processed and stored, a study should be made as to which properties of dusts generated in those conditions cause an increased danger of explosion and fire.
Methodology: To determine the flammability and ignitability of the analysed samples of flour dusts, the following tests were performed: determining the minimum ignition temperature of dusts igniting from a heated surface in accordance with PN-EN 50281-2-1:2002, specifying the ignition temperature of thermal decomposition products according to PN-69/C-8902, thermogravimetric analysis in line with PN-EN ISO 11358-1:2014, and determining combustion heat according to PN-EN ISO 1716:2010. The presented values included the minimum ignition temperatures of layers and clouds, the ignition temperature of the flammable gaseous phase and the value of combustion heat. A thermogravimetric analysis was carried out of five types of food products used, inter alia, in the catering industry, food industry and in households, including wheat, chickpea, oat, rice and maize flour.
Results: It was found that among all the tested types of dusts the chickpea flour dust causes the highest fire hazard. It has the lowest temperature of ignition and of the onset of thermal decomposition, and the admissible temperatures of the surface of appliances operating in the presence of this dust, for a layer of 5 mm and 12.5 mm may not exceed 245˚C and 200˚C, respectively.
Conclusions: The conducted experimental tests allow minimising the hazards and justify the necessity of ensuring a particularly thorough and frequent removal of accumulated dusts, respecting technological regimes and the required frequency of inspections and maintenance activities of all machines and appliances used in the technological process. The dusts of flours made of wheat, maize and rice were found to have similar physicochemical and flammable properties, which may be seen in the example of the bulk density value, ignition temperature, minimum cloud ignition temperature and the initial temperature of thermal decomposition. Given the value of combustion heat and fire load density, it was found that rice flour offers the most favourable parameters. The highest ignitability of the gaseous phase by a small flame among the tested types of flour was found for oat flour.
Keywords: dust ignitability, fire safety
Type of article: original scientific article