Abstract
Hot surfaces are an integral part of the technological processes of agricultural crop processing. Their surface temperature at critical points can exceed the minimum ignition temperature. This paper aims to experimentally observe the behaviour of hay when exposed to radiant heat. The model presented here is implemented using a hot plate device. The hot plate has a defined temperature-time curve. Based on the above, the hot plate temperature is determined as the minimum ignition temperature of the investigated hay specimen. At the same time, the temperature inside the tested material was monitored. The heterogeneity of the above specimens significantly influenced the nature of the biomass thermal degradation. The ignition temperature of the hay (406 °C) can serve as a tool for fire risk assessment.
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Determination of the Ignition Temperature of Hay for the Purposes of Fire Risk Assessment on Farms – Slovak Case Study
Iveta Marková,a,* Patrik Mitrenga,a Linda Makovická Osvaldová,a and Helena Hybská b
Hot surfaces are an integral part of the technological processes of agricultural crop processing. Their surface temperature at critical points can exceed the minimum ignition temperature. This paper aims to experimentally observe the behaviour of hay when exposed to radiant heat. The model presented here is implemented using a hot plate device. The hot plate has a defined temperature-time curve. Based on the above, the hot plate temperature is determined as the minimum ignition temperature of the investigated hay specimen. At the same time, the temperature inside the tested material was monitored. The heterogeneity of the above specimens significantly influenced the nature of the biomass thermal degradation. The ignition temperature of the hay (406 °C) can serve as a tool for fire risk assessment.
DOI: 10.15376/biores.17.4.6926-6940
Keywords: Hay; Fire risk; Hot surfaces; Ignition temperature
Contact information: a: Department of Fire Engineering, Faculty of Security Engineering, University of Žilina, 010 26 Žilina, Slovakia, b: Department of environmental engineering, Faculty of Ecology and Environmental Sciences, Technical University in Zvolen, 960 01 Zvolen, Slovakia;
* Corresponding author: iveta.markova@uniza.sk
INTRODUCTION
Agriculture has undergone a significant change in terms of the work organisation. Today, agricultural production is carried out through medium and small enterprises (SBA 2021). Although the production and breeding of agricultural animals are decreasing (Statistical Office of the Slovak Republic 2022b), the risk of the fire remains The European Green Deal policy favours the use of agricultural products (EC 2019). Concerning renewable sources, biomass is used as a fuel (Mullerová et al. 2010; Martiník et al. 2014; Marková et al. 2018a), while it is also promoted in the construction industry as an innovative natural insulation material (Daňková and Hejhálek 2009; Cascone et al. 2019; Tobias and Writer 2020). The fact that it is a material that does not resist heat must be considered (Preventing fires in baled hay and straw 2012; Štulajter et al. 2015; Čekovská et al. 2017; Marková et al. 2018b; SDSU Extension 2020). The impact of burning and fire suppression on aquatic and terrestrial environments also requires attention (Veľková et al. 2019; Hybská et al. 2020, 2022).
From an occupational health and safety perspective, agriculture and forestry are highly problematic sectors that require increased attention. As the graph of the enterprise development in agriculture, forestry and fishing (Fig. 1) demonstrates, the number of these enterprises is increasing in the long term, as indicated by the trend line with high reliability (R2= 0.95). Over the last decade, more than 3000 enterprises have emerged in that sector. The majority of them are small enterprises (EU-OSHA 2021).
Fig. 1. Development of enterprises in the section of agriculture, forestry and fishing over the last decade (Statistical Office of the Slovak Republic 2022a).
Another reason why increased attention needs to be paid to safety in this sector is a large number of occupational accidents, including serious and fatal ones. Figures 2 and 3 indicate the total number of accidents in each division of the statistical classification of economic activities (SK NACE) for the last decade (2012-2021). Only the first 6 divisions with the highest number of injuries are demonstrated.
Fig. 2. Number of registered occupational injuries (ROIs) in selected SK NACE divisions with the highest number of injuries over the last 10 years (2012-2021) (Source: Statistic of occupational injuries 2012 – 2021)
Fig. 3. Number of serious occupational injuries (SOIs) and fatal occupational injuries (FOIs) in selected SK NACE divisions with the highest number of injuries over the last decade (2012-2021) (Source: Statistic of occupational injuries 2012 – 2021)
Figure 2 indicates that the highest number of registered occupational injuries (injuries in which the incapacity for work lasted more than 3 days, hereafter referred to as ROIs) – 7061 over the last decade were in the retail trade division. The six most risky divisions in terms of the number of ROIs, with a total of 4063 such injuries, include Crop and Animal Production, which falls under the Agriculture, Forestry and Fishing Section. This division is also ranked fourth in terms of the total number of serious occupational injuries (SOIs) – 70 (Fig. 3). Of these, as many as 35 were fatal (hereafter referred to as fatal SOIs), which is a relatively high number compared to the other divisions. Although there were almost two-thirds more fatalities in land transport, these were mainly road traffic accidents. The Crop and Animal Production Division can be considered the riskiest within the Agriculture Section. Figure 4 below demonstrates the injury proportions in each sub-classes of this division.
Fig. 4. Percentage of injuries in each subclass of the division ‘Crop and Animal Production, Hunting and Related Service Activities’ over the last decade (2012-2021) (Source: Statistic of occupational injuries 2012 – 2021)
The highest proportion of occupational injuries, 41%, within the division of Crop and Animal Production, Hunting and Related Service Activities occurs in dairy cow farming. It is followed by cereal farming with an injury rate of 25% and mixed farming with an injury rate of 17%. According to the National Labour Inspectorate, fire hazards are among the most common hazards and dangers in agriculture (Gubrica 2016). Increased fire hazards occur especially during the harvesting of cereals, their post-harvest treatment, and the storage of coarse fodder and straw. These are also used in dairy farming (straw for bedding and hay for fattening), where the highest proportion of occupational accidents occurs.
Figure 5 demonstrates the use of cereal harvesting areas, which pose an increased risk of fire (Holla et al. 2017; Vogel and Annen 2018). In 2021, the harvested area of all cereals amounted to 717694 ha.
Fig. 5. Harvested area of cereals in particular years (Statistical Office of the Slovak Republic 2022c)
Fig. 6. Fire incidence in the Slovak Republic over the last five years (Source: Fire statistics of the Fire and Rescue Corps 2016 – 2021)
The above fact is confirmed by fire statistics obtained from the Fire Technical and Expertise Institute of the Ministry of the Interior of the Slovak Republic (Fig. 6). Although the number of fires has a decreasing tendency, agricultural fires maintain their respective percentage (11-5%). At the same time, Fig. 7 shows the number of fires based on their causes. During spontaneous combustion and subsequent hay fires, heterogeneous forms of combustion, primarily smouldering, dominate. Smouldering produces large amounts of dense, light smoke.
Fig. 7. Monitoring the number of fires by cause of fire in the Slovak Republic over the last five years (Source: Fire statistics of the Fire and Rescue Corps 2016 – 2021)
Hot surfaces are an integral part of biomass processing processes. Their surface temperature can exceed the minimum biomass ignition temperature. Biomass ignition depends on external conditions, but the initiation temperature at which ignition occurs remains the decisive parameter.
This paper aims to experimentally determine the ignition temperature of hay due to the action of radiant heat and cigarettes. Moreover, based on the obtained results, it aims to verify the developed Slovak standards concerning preventive measures regarding the risk of hay fire.
EXPERIMENTAL
Materials
For the experiment, hay specimens obtained from the farm were utilized (Fig. 8c). They were stored in bales and used for running the cow house.
Hay is a green fodder preserved by natural drying or desiccation. Besides fresh green fodder, hay is the most natural feed suitable for all livestock species (Kováč et al. 1989). Hay is the dry above-ground parts of plants that are preserved by drying and partial fermentation and, when stored appropriately, represents a long-term supply of high-quality dry roughage (Straková et al. 2008).
It is necessary to dry the cut material, i.e. to get rid of excess water. This process, which increases the dry matter, is the elementary preservation of hay for long-term storage. The water content of the hay drops to 9-10%. The hay is stored in haylofts with a slatted floor with tunnels into which heating fans blow air, speeding up the drying process.
Hay dried in this way is transported to the cow shed: 1. by pneumatic filling and mechanical emptying (Ďuďák 2022a), 2. by a mixing feed truck (Fig. 8a) (Cow feeding and watering, 2022), 3. by a drive-through feed chute (Herman 2017), or 4. by an electric feed truck by vehicle (Fig. 8b) (Ďuďák, 2022b). Feed must be available to all animals.
Fig. 8. Demonstration of feed transport by mixer feed truck (Cow feeding and watering, 2022); (b) Robot feed transport (Cattle feeding, 2022); c) Test specimen.
The hay samples were provided by the agricultural company Agrodružstvo Bánová, Slovak Republic. The samples were dried and stored according to the instructions in Decree of the Ministry of the Interior of the Slovak Republic No. 258/2007 Coll. As stated by the representative of Agrodružstvo Bánová, Slovak Republic, the moisture of the tested samples is 11%.
Methodology
The determination of the minimum ignition temperature of the organic matter layer was conducted by isothermal stressing of the specimen placed on an electrically heated metal hot plate (Fig. 9) and continuous temperature measurement inside the specimen. The minimum combustion initiation temperature is defined as the lowest surface temperature of the hot plate at which at least one of the following phenomena can be observed during the test:
- Glowing, smouldering or flame burning;
- Time-temperature curve for a thermocouple placed in the centre of the specimen layer rises continuously compared to the temperature of the isothermally heated plate;
- Temperature measured in the deposited dust layer is 250 °C higher than the hot plate temperature.
In the conducted experiments, the above conditions were fulfilled.
Fig. 9. Hot plate
Hot plate calibration was performed at the beginning of the experiment. The obtained temperature-time curve (Fig. 10) is the basis for the measurement of the ignition temperature according to EN 50281-2-1 (1998).
Subsequently, selected biomass specimens were exposed to the thermal surface. The experiments were performed t at T=21 °C and pressure of 100.56 kPa. They were repeated 3 times.
Fig. 10. Dependence of the temperature rise of the hot plate surface on time
The second part of the experiment was based on observing the behaviour of a hay specimen on which a cigarette was placed. The hot plate device was left off as it served as a pad for depositing the specimen.
During the experiment, two temperature values were measured by thermocouples:
1. Surface temperature of the hot-plate;
2. Temperature inside the sample (by thermocouple placed inside the sample).
RESULTS AND DISCUSSION
Table 1 demonstrates the measured values of the minimum ignition temperatures of the hay specimens, the temperatures measured inside them, and a description of the behaviour of the hay layer during its thermal stress and the moment of ignition. The visualization is accompanied by photo documentation (Fig. 11). The specimen weight was increased by 1g. This fact was not reflected in the experiment.
Table 1. Summary of the Results Obtained for the Determination of the Ignition Temperature of Hay
