Assessment of the Radioactivity, Metals Content and Mineralogy of Granodiorite from Calabria, Southern Italy: A Case Study.

In this paper, an assessment of the natural radioactivity level, radon exhalation, metal contamination, and mineralogy of a granodiorite rock sample from Stilo, in the Calabria region, Southern Italy is presented as a case study. This rock was employed as a building material in the area under study. The specific activity of 226Ra, 232Th and 40K natural radioisotopes was assessed through high-purity germanium (HPGe) gamma-ray spectrometry. Then, several indices such as the absorbed gamma dose rate (D), the annual effective dose equivalent (AEDE), the activity concentration index (ACI) and the alpha index (Iα), were quantified to determine any potential radiological health risk related to radiation exposure from the analyzed rock. Furthermore, E-PERM electret ion chambers and inductively coupled plasma mass spectrometry (ICP-MS) measurements were carried out to properly quantify the radon exhalation rate and any possible metal pollution, respectively. In particular, to further address metal pollution factors, the geo-accumulation index (Igeo) was calculated to properly address the toxicity levels of the ecosystem originating from the detected metals. Finally, with the aim of successfully discriminating the provenance of such naturally occurring radionuclides, a combined approach involving X-ray diffraction (XRD) and µ-Raman spectroscopy was employed for the identification of the main radioisotope-bearing minerals characterizing the investigated granodiorite. The results achieved in this case study can be taken as the basis for further inquiries into background levels of radioactivity and chemical contamination in natural stone employed as building materials.

Evaluation of accurate measurement methods for radon exhalation rate with advection effect and application in field.

In decommissioning of a uranium tailings pond, radon exhalation rates on a beach surface should meet regulatory standards. Accurate measurements of the radon exhalation rate are demanded. However, current studies fail to consider the impact of advection under temperature variations or pressure gradients caused by gas movement on measurements using an accumulation chamber. Two proposed methods were therefore evaluated to accurately measure radon exhalation rates on the loose medium surface under advective conditions. Repeated experiments were conducted on a laboratory experimental platform filled with uranium tailings sand under advective flow rates of 0.03 and 0.3 L/min to validate the stability and reliability. Deviations between measured and true values were 0.1-6.1 % and 6.3-29.2 % for the two methods, respectively. Subsequently, numerical simulation was used to analyze defects of traditional methods and mechanisms of the new methods. In a field study, all methods were compared, and a predictive map of radon exhalation rates was created using interpolated data from 20 random sites using the new method. Results from the proposed methods, compared with traditional ones, were closer to true values under advective conditions, and accurate assessment of beach surface treatment was expected.

Study on the influence of water saturation on radon exhalation rates of rocks.

The radon exhalation characteristics of rocks will change significantly during water saturation treatment, and radon, as an important tracer, is of great significance in predicting rock activities. In this paper, the radon exhalation characteristics of rocks after saturated with different water contents were studied by centrifugal test, radon measurement test and other indoor tests. The results show that the radon exhalation rate of rocks shows a rising and then decreasing trend with the increase of rock water saturation. The radon precipitation rate peaked at 0.7 Sw âˆ¼ 0.8 Sw, and the high water saturation had an obvious inhibiting effect on the radon exhalation rate of rocks. The research results are of great significance in predicting the rock-water-based geological processes.

Effect of hygroscopicity of typical powder solid wastes on their radon exhalation characteristics.

The characteristics of radon exhalation in the hygroscopic properties of powder solid wastes are immensely significant for environmental safety and their transportation, storage, and landfill. This study detected the radon concentration of superfine cement and five kinds of powder solid waste: fly ash, silica fume, coal gangue, S95 mineral powder, and molybdenum tailing powder, at different hygroscopic times for 1-5 d under 95 % relative humidity. Additionally, the influence of particle size and porosity of solid waste on radon exhalation characteristics was analyzed using a laser particle size analyzer and nitrogen adsorption technology. The results show that the radon exhalation rate of the solid waste was at a low level in dry conditions. Although the presence of water due to the increased moisture absorption rate inhibited the radon exhalation to a certain extent, it was higher than that in dry conditions. The reciprocal of the moisture absorption rate had a strong linear relationship with the ratio between the radon exhalation rate after hygroscopy and radon exhalation rate from dry materials. The pore structure has a significant effect on the exhalation rate of radon, and the macropores inhibits the exhalation rate of radon. The results of this study have guiding significance for the reuse of solid waste and the prevention of radiation risk of radon exhalation during transportation.

Radon Exhalation Rate: A Metrological Approach for Radiation Protection.

Radon, a radioactive inert gas that comes from the decay of naturally occurring radioactive species, poses a substantial health risk due to its involvement in lung cancer carcinogenesis. This work proposes a metrological approach for determining radon exhalation rates from diverse building materials. This methodology employs an electrostatic collection chamber for alpha spectrometry of radon isotopic decay products. Experimental evaluations were conducted particularly focusing on volcanic gray tuff from Sant'Agata de' Goti (Campania region, Italy), a material commonly utilized in construction, to assess radon exhalation rates. The study aligns with Legislative Decree 101/2020, a transposition of European Directive 59/2013/Euratom, highlighting the need to identify materials with a high risk of radon exhalation. Moreover, this work supports the goals of the Italian National Radon Action Plan related to the aforementioned decree, aiming to develop methodologies for estimating radon exhalation rates from building materials and improving radioprotection practices.

Theoretical model for calculating and adjusting radon activity concentration in ventilation networks of uranium mines considering pressure drop effect.

The radiation dose of workers in underground uranium mines mainly comes from radon and radon progeny. To ensure a healthy and safe work environment, it is necessary and urgent to optimize the design of ventilation systems. As such, based on the simplified radon diffusion-advection migration model of the rocks, this paper proposes 1) two methods for determining the radon exhalation rate modified by pressure drop, 2) three methods for calculating radon activity concentration of single-branch, and 3) the novel adjustment algorithm and solving procedures for calculating and adjusting the radon activity concentration in ventilation networks by modifying the radon exhalation rate, demonstrated on a specific ventilation network in a simulated underground uranium mine with calculation and analysis via MATLAB. The results show that 1) the radon exhalation rate of different branches can be modified by their pressure drop, and 2) the proposed method can be used to reveal the influences of different ventilation methods and fan pressures on the radon activity concentration in the ventilation network and the radon release rate to the atmosphere.

Influence of rock type and geophysical properties on radon flux density.

The most significant source of human exposure to ionizing radiation is the radioactive gas radon (basically 222Rn) and its daughter decay products, creating more than half of the effective dose from all natural sources. Radon enters buildings mainly from dense rocks, which are below building foundations at depths of 1 m and more. In this paper long-term measurements of radon flux density are analyzed, with radon exhalation from the surface of the most common rocks-loams, sandy loams, clays, clay shales, several types of sandy-gravel-pebble deposits, clay and rocky limestone. The influence of geophysical properties of rocks on radon flux density due to exhalation from surfaces of those rocks was studied. Based on the results obtained, a method of local assessment of the hazard from radon and its progeny in buildings is proposed, which is based on the geophysical properties of rocks below the foundations of those buildings.

Novel approaches for accurately measuring radon exhalation rate and mechanism interpreted by numerical simulation.

Measurements of radon exhalation rate using traditional methods can be affected by back-diffusion or differential pressure in the accumulation chamber, resulting in deviations between the measured and the true values. To obtain an accurate radon exhalation rate for evaluation of radon-risk regions, two novel approaches of measurements based on traditional methods were proposed. Repeated experiments were implemented on a self-designed stainless cylindrical vessel filled with uranium tailings sand. The measured radon exhalation rates on average were 0.51 ± 0.02 and 0.52 ± 0.02 Bq m-2 s-1 for the two proposed methods, with 0.02% and 0.04%, respectively, deviations from the theoretical value. In addition, numerical techniques were employed to interpret the defects of traditional methods and mechanisms of proposed approaches to measure accurate values. Two novel approaches have significantly reduced the impact of back diffusion and differential pressure inside the chamber and consumed less time.

Numerical simulations of radon exhalation from surrounding rocks of single and double underground roadways.

The radon exhalation rate of surrounding rocks in underground roadways is an important parameter in determining radon exhalation capacity and ventilation flowrate for radon removal. By approximating the roadways as thick-walled, porous cylinders, this study investigates radon exhalation from their surrounding rocks via simulations using computational fluid dynamics (CFD). Radon exhalation rates of single and double underground roadways were computed and analysed under different pressure differences, radon diffusion coefficients, permeabilities of rocks, single roadway locations and additional parallel roadway orientation. The radon regulating zone was presented and the effect of pressure difference on it was analysed. By fitting the data from simulation results, an estimation model was obtained for the radon exhalation rate of a single roadway. For two adjacent parallel roadways with a distance greater than or equal to 50m, the model is also suitable for estimating the radon exhalation rate when the rock permeability is less than 1 × 10-14 m2 and the ratio of permeability to diffusion coefficient is less than 5 × 10-9.

Radiometric analysis of Brazilian commercial ornamental stones.

The term "commercial ornamental stones" comprises different natural stones with different mineralogical components and the distribution and amount of natural radionuclides depended on the mineralogy. Few studies on natural radioactivity in ornamental stones carried out in Rio de Janeiro (Brazil) and the present work were carried out in order to analyze the distribution of activity concentration in these materials. The activity concentration of 238U, 235U, 226Ra, 232Th and 40K in Ornamental Stones measured using γ-ray spectrometry to estimate the radiation hazard as well as establishing a database for radioactivity levels. Samples were collected in stores in Rio de Janeiro, carefully transported, weighed, packed with PVC film and left to rest for at least 45 days to reach secular equilibrium. Samples analyzed by gamma spectrometry using a hyper pure germanium detector (HPGE). Detection efficiency for each sample was obtained using LabSOCS software. The activity concentrations for samples were within the ranges (0.83 ± 0.15 to 39.96 ± 1.19, 8.04 ± 2.54 to 111.36 ± 13.33, 0.43 ± 0.03 to 264.58 ± 0.98, BDL to 8.17± 0.65 and 1.30 ± 0.57 to 1567.01 ± 65.08) Bq⋅kg-1 for 238U, 226Ra, 232Th, 235U and 40K, respectively. The world average for building materials is 50 Bq⋅kg-1 for 238U, 50 Bq.kg-1 for 232Th and 500 Bq⋅kg-1 for 40K. In the present work, the average for granite was 19.43 ± 0.39 Bq⋅kg-1 for 238U, 56.70 ± 1.13 Bq⋅kg-1 for 232Th and 1113.28 ± 20.27 Bq⋅kg-1 for 40K, thus the values for 232Th and 238U are above the world average. Analyzing for the granite that showed the highest concentrations of activity the average values of Transport Rate was 3.12 ± 0.04 Bq⋅m-2⋅s-1, Emanation Rate was 0.16 ± 0.00 Bq⋅kg-1⋅s-1, Exhalation Flow was 530.26 ± 6.05 Bq⋅m-3, Effective Equivalent Dose Due to Radon Exposure was 0.78 ± 0.01 WLM⋅year-1 and Annual Effective Dose Due to Radon and Thoron was 7.02 ± 0.10 mSv⋅year-1. Annual Effective Dose Due to Radon and Thoron it is above the annual limit for public individuals which is 1 mSv⋅year-1 and below the occupationally exposed individual, which is 20 mSv⋅year-1 in an average of 5 years, it does not exceed the maximum level recommended by ICRP-60.

Radon exhalation characteristics after pyrolysis of long flame coal.

Coal pyrolysis is a important method for classifying and utilizing coal resources and contributes to enhanced comprehensive resource utilization. However, In high-temperature areas such as coal pyrolysis, there is an abnormal phenomenon release of radioactive gas radon, understanding the relationship between temperature and radon exhalation characteristics, as well as the underlying mechanisms, holds great importance for assessing radon pollution in mining areas. After coal undergoes pyrolysis under high temperature conditions, its material composition, pore structure, water content, and other properties have changed. The pyrolysis products in different atmosphere environments have differences, and the characteristics of radon emission are also different. To address this, the present study conducted coal pyrolysis experiments in both aerobic and anaerobic environments, using long flame coal sourced from Yulin, China. The radon release concentration of the pyrolysis products was measured. The research findings indicate that during pyrolysis at elevated temperatures, the ratio of coal mass loss is constantly increasing. High temperatures promote the development of pores and fissures, and significant changes in coal properties at temperature thresholds (300 °C and 500 °C). The specific surface area, pore volume, and fracture ratio all display substantial increases, and the amplitude of change is greater under aerobic conditions. The fractal dimension of total pores and macropores shows continuous growth, while the specific surface area, pore volume, and fracture ratio exhibit a strong negative correlation with the radon emission rate of pyrolysis products. The expansion and penetration of pores and cracks, along with the release of a substantial amount of pyrolysis gas, accelerate the transformation, migration, and exhalation of radon, resulting in a negative correlation between the heat treatment temperature and the radon release rate of pyrolysis products. Under aerobic conditions, the radon release rate of pyrolysis products decreases more significantly.

Long-distance migration law of radon in overburden of abandoned goaf during coal spontaneous combustion.

The surface isotope radon measurement method (SIRMM) is widely used in fire source detection in abandoned mines. However, studies on the long-distance migration of radon during coal spontaneous combustion are lacking, which hinders the further popularization of this technology in coal fire prevention and control. For this reason, the migration law of radon in overlying strata in fire areas was studied through experiments and numerical simulation. The radon exhalation concentration of coal was found to increase at first and then decrease in the range of 30-350 °C through experiments. The radon concentration reaches the maximum value (557.1 Bq/m3) at 150 °C, which is 6.3 times higher than that at 30 °C. Based on the radon source term obtained by fitting the experimental data, the radon migration model of coal spontaneous combustion in abandoned goaf was constructed, and the dynamic distribution characteristics of the airflow, temperature, and radon concentration fields in the overlying strata area were analyzed. The internal relationship between surface radon and underground fire source was discussed. The simulation results revealed the sharp change in the porosity of the overlying rock causes radon concentration at the interface between the caving and fissure zones to increase continually with the process of spontaneous combustion, providing material and energy support for the long-distance radon migration. When the maximum temperature of the coal pile reaches 70 °C, the concentration of radon released from the coal pile increases rapidly to 13696 Bq/m3, and the radon from the underground space appears on the surface at this temperature. In the range of 70-150 °C, with rapid increase in radon released from coal piles, the surface concentration of radon also increased rapidly to 225 Bq/m3. At the high-temperature stage exceeding 150 °C, the concentration of radon released from coal piles exhibited a downward trend, resulting in a decrease in the rate of increase of radon concentration on the surface. A close relationship between the surface radon concentration and underground fire source temperature in the process of coal spontaneous combustion was observed. In the spatial position, the peak position of radon on the surface was highly consistent with that of the fire source longitudinally, which ensures the accuracy of the SIRMM to determine the location of the hidden fire source. This suggests that the SIRMM can accurately evaluate the fire source's temperature and fire area's development trend.

Unraveling the complex interplay between soil characteristics and radon surface exhalation rates through machine learning models and multivariate analysis.

This research seeks to elucidate the intricate interplay between soil characteristics and the rates of radon surface exhalation rate. To achieve this aim, Light Gradient Boosting Machine (LightGBM) and eXtreme Gradient Boosting (XGBoost) machine learning (ML) algorithms are employed, supported by Multivariate Analysis (MA). An analysis was performed on a collection of soil samples, examining radon surface exhalation rates and other pertinent properties such as moisture content, particle size distributions, and the concentrations of Ra-226, Th-232, and K-40. The analysis revealed several key factors influencing radon exhalation rates, namely Ra-226 concentration, moisture content, and larger soil particles. To visualize the intricate relationships between these variables, contour plots of experimental and ML-generated data were created. These visual representations demonstrated that elevated soil moisture levels decrease radon exhalation rates. In contrast, higher concentrations of Ra-226 and a greater proportion of large soil particles led to an increase in exhalation rates. This endeavor presents these complex relationships in an accessible manner, furthering our understanding of the factors in radon surface exhalation. MA techniques, including Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA), were initially employed to investigate the complex interactions of soil attributes on radon exhalation. HCA identified three distinct clusters but faced limitations in detecting strong negative impacts. PCA successfully captured these inverse effects, indicating that the first two principal components accounted for approximately 80% of the total variance, primarily attributed to Ra-226 concentration, moisture content, and the percentage of large soil particles. However, neither technique could quantify the effects of soil attributes on radon exhalation rates. LightGBM outperformed XGBoost, but both successfully quantified the impacts of the studied soil characteristics on radon exhalation. Sensitivity analysis confirmed the robustness and accuracy of both models. This study highlights that XGBoost and LightGBM algorithms can effectively quantify radon exhalation rates based on soil characteristics, providing valuable insights for environmental policies, land use planning, and radon mitigation strategies.

A new model to accurately measure the radon exhalation rate from soil using AlphaGUARD.

Radon exhalation rate from soil is a critical factor in evaluating environmental radon levels. However, AlphaGUARD PQ2000PRO may have some sensitivity towards thoron, which can have a significant impact on radon measurement. The traditional radon exhalation models generally ignore the presence of thoron, leading to an overestimation of the radon exhalation rate from soil. To handle this issue, a new model was proposed based on an analysis of several previous studies on radon exhalation theories. To prove the feasibility of the model, the radon exhalation rate measurements were performed by two different types of detectors-AlphaGUARD PQ2000PRO and RAD7. The radon exhalation rate obtained by using the new model is in good agreement with that obtained by using the theoretical model of radon exhalation of RAD7 within one standard error. This new model can be applied to accurately measure radon exhalation rate from soil by the PIC detector (PQ2000PRO).

Models of radon exhalation from building structures: General and case-specific solutions.

Assessing the radon activity that exhales from building structures is crucial to identify the best strategies to prevent radon from entering a building or reducing its concentration in the inhabited spaces. The direct measurement is extremely difficult, so the common approach has consisted in developing models describing the radon migration and exhalation phenomena for building porous materials. However, due to the mathematical complexity of comprehensively modelling the radon transport phenomenon in buildings, simplified equations have been mostly adopted until now to assess the radon exhalation. A systematic analysis of the models applicable to radon transport has been carried out and it has resulted in four models differing in the migration mechanisms - only diffusive or diffusive and advective - and the presence of inner radon generation. The general solutions have been obtained for all the models. Moreover, three case-specific sets of boundary conditions have been formulated to account for all the actual scenarios occurring in buildings: both perimetral and partition walls and building structures in direct contact with soil or embankments. The corresponding case-specific solutions obtained serve as a key practical tool to improve the accuracy in assessing the contribution of building materials to indoor radon concentration according to the site-specific installation conditions in addition to the material inner properties.

Radon exhalation from cement-based materials under accelerated carbonation.

Cement-based materials manufactured from rocks and soils will release radon which is a carcinogen and affects indoor air quality. The alkaline cement-based material neutralizes with the acidic gas carbon dioxide in the air, reducing its pH value, known as carbonation. Carbonation of cement-based materials is an important environmental factor that can change the pore structure and effect radon release. In this study, test blocks of concrete, fly ash concrete, cement mortar, and cement paste were subjected to carbonation at 20 vol% CO2, 70% relative humidity, and a temperature of 20 ± 2 ℃ for 28 days to explore the effect of material characteristics and carbonation age on the radon exhalation rate. Carbonation had a significant influence on the radon exhalation rate, but this effect showed positive (promoting/increasing) and negative (inhibiting/decreasing) fluctuations with carbonation age. Among the material characteristics, aggregate content had the most significant influence, followed by fly ash and cement variety. The radon exhalation rate was ordered as cement mortar > concrete > cement paste before carbonation, but was concrete > cement mortar > cement paste after carbonation. The radon exhalation rate of cement paste blocks without aggregate was ~ 1 mBq/(m2·s) lower than that of cement mortar. The inhibition of radon emission by concrete was mainly observed in the early carbonation period (< 7 days), while that by fly ash concrete was observed after 7 days. The content of fly ash did not have a significant influence on the radon exhalation rate of materials. Radon inhibition by composite Portland cement concrete was mainly observed in the middle stage of carbonation (~ 14 days), while inhibition by ordinary Portland cement concrete was mainly observed in the early (3-7 days) and late (i.e., ~ 28 days) stages. The water/binder ratio did not significantly affect the radon exhalation; concrete with a low water/binder ratio showed weak radon inhibition only when the carbonation age was long. These results will help to evaluate radon pollution in indoor or underground environments under long-term use.

Evolution of pore structure and radon exhalation characterization of porous media grouting.

Cracks and pores are considered as major sources of radon. Cement is widely used as a grouting material in mines, tunnels, and other projects for reinforcement, seepage prevention, and water plugging. This paper mainly experimentally studied the correlation between the radon exhalation rate of the porous medium after grouting and the sand grain diameter, grouting pressure, and slurry water-cement ratio. The pore characteristics of the samples before and after grouting were also studied based on the low field nuclear magnetic resonance (LF-NMR). The findings of the study show that the porosity of samples increases after the superfine cement solidification with an increase in the water-cement ratio, and the radon exhalation rate is proportional to porosity, the radon exhalation rate increases by 0.0005 Bq·m-2/s at W/C = 1.5, and by 0.0017 Bq·m-2/s at W/C = 2 increases, in comparison to the W/C = 1.The radon exhalation rate of porous media gradually increased after grouting in response to an increase in grouting pressure and the water-cement ratio. The radon exhalation rate of the porous media with larger pores was relatively higher and exhibited a positive correlation with the volume of micropores in porous media，the correlations of coarse, medium and fine media are 0.815, 0.826, and 0.859. The change in pore structure has an influence on radon exhalation. Although grouting changes the pore structure and reduces the connectivity between internal pores, the micropores generated after cement slurry solidification improves the radon exhalation rate by providing new channels, When the water-cement ratio is 1.5 and the grouting pressure is 1.5 MPa, the radon exhalation rate of porous media is 0.00273 Bq·m-2/s. The research results serve as a reference basis for the evaluation of the impact of rock masses on grouting reinforcement and pore sealing.

Radiological assessment of urban soil samples in the residents of a central Anatolian volcanic province, Turkey.

The concentration of natural and anthropogenic radionuclides, emanation fraction (EF), and mass (χM) and area (χA) exhalation rate of 222Rn in urban soil samples collected from dwelling areas in Nevsehir city located in a region known as the central Anatolian volcanic province of Turkey were determined using gamma-ray spectroscopy. The average activity concentrations of 226Ra, 228Ra, 40K and 137Cs were measured as 60.2 ± 3.8, 50.1 ± 2.8, 631.0 ± 29.7 and 5.5 ± 0.4 Bq/kg, respectively. The average concentration of 222Rn in soil and air was estimated as 27 kBq/m3 and 84 Bq/m3, respectively. The average values of EF, χM and χA were found as 20%, 25.4 µBq/kg⋅s and 20.2 mBq/m2⋅s, respectively. The average values of outdoor absorbed gamma dose rate, external and internal annual effective dose and lifetime cancer risk estimated for radiological assessment were found as 85 nGy/h, 104 µSv/y, 797 µSv/y and 4.1 × 10-4, respectively.

A study on radon diffusion and exhalation of soils under transient conditions: Theoretical and experimental approach.

A practical method is presented for the short-time transient-diffusion measurement of radon flux and concentration in large soil samples (porous materials) and the radon diffusion coefficients. An experimental apparatus was designed and tested to verify the theoretical validity and technical accuracy of the presented technique by the transient-diffusion method. The concentration data measured inside the accumulator determines the radon flux for various soil thicknesses. Good agreement was observed between values of the measured radon flux and those expected by the theoretical model based on the diffusion theory. The relative standard deviation of 16% was obtained in measurements with dry soil by the short-time transient-diffusion method. Diffusion coefficients of soils were derived from the curve fit of measured flux data to the theoretical expression based on Fick's law. Comparing the measured diffusion coefficient and that obtained by empirical correlation provides a good agreement with a relative uncertainty of 11%. The present transient-diffusion measurement technique could provide low cost, good precision, short time experiment, no radioactive waste (residue) generation, and good validity.

Study on the characteristics of radon exhalation from rocks in coal fire area based on the evolution of pore structure.

Radon is of great significance as a tracer for the detection of coal fires due to its distinct variations in radon exhalation properties while heating. The research on radon exhalation performance through pore structure is still in its early stages. In this paper, the pore structure and radon exhalation characteristics of heat-treated limestone are studied using indoor tests such as nuclear magnetic and radon measurements. The study's results demonstrate that the radon exhalation rate of limestone initially increases gradually, followed by a steady decline and subsequent increase with the increase in temperature. The radon exhalation rate at 800 °C reaches 2.42 times that at room temperature. The pore structure change within limestone strongly correlates with the radon exhalation rate. The pore volume of micropores (<0.1 µm) plays an essential role in the radon exhalation capacity, which is directly related to the fractal dimension of micropore structure in the heated limestone. The study's findings can be used to identify coal fires.