Experimental Study on Thermal Properties and Fire Risk According to Acid Value Change in Palm Oil

Abstract

(1) Background: this study investigates the impact of acid value changes on the thermal degradation and fire risks of palm oil. It emphasizes the need for systematic risk management in food manufacturing and preparation processes to address safety challenges associated with high-temperature operations. (2) Methods: the study employed fire reproduction experiments, fire risk characterization tests, and thermal analyses, including differential scanning calorimetry and thermogravimetric analysis. (3) Result: higher acid values in palm oil significantly reduce smoke points, ignition points, and thermal stability, primarily due to increased free fatty acids and oxidative by-products. These effects are more pronounced in oxidative environments, highlighting the importance of controlling acid value to mitigate fire and thermal risks. (4) Conclusions: this study concludes that increased acid value in palm oil significantly reduces its thermal stability and elevates fire risks due to accelerated oxidation and thermal decomposition. It emphasizes the importance of monitoring acid value and implementing temperature control measures to enhance safety in food manufacturing and cooking processes.

1. Introduction

Food manufacturing and preparation are essential activities in modern society, playing a pivotal role in providing flavor and nutrition while shaping culinary culture [1,2,3]. However, the chemical and physical reactions occurring during these processes can often pose unforeseen risks [4,5]. In particular, the use of high temperatures during food processing can lead to thermal decomposition and oxidation [6,7], resulting in the formation of toxic chemicals and increased fire risks [8]. As the complexity of food manufacturing processes grows and the consumer demands diversify [9], ensuring safety in these operations is becoming a critical challenge.

Edible oils, particularly palm oil, are essential in modern food preparation and production, frequently used in high-temperature processes like frying, baking, and sautéing. [10]. Palm oil is favored in various industries due to its superior thermal and oxidative stability, as well as its economic advantages [11,12]. Thermal stability refers to palm oil’s ability to resist decomposition at high temperatures. This is largely due to its high saturated fatty acid content, which is structurally stable and less prone to degradation. Oxidative stability is the resistance to rancidity caused by oxygen exposure. It allows palm oil to maintain quality, flavor, and safety during extended storage. However, repeated use or prolonged exposure to elevated temperatures induces oxidation and thermal degradation in palm oil [13]. These processes lead to the generation of volatile compounds, the formation of toxic substances, and a reduction in the flash point, thereby increasing its potential as a fire risk rather than a safe cooking medium.

Recent fire statistics in South Korea over the past three years reveal that kitchen fires account for 16.1% of all fires, making them one of the leading causes of fire incidents [14]. Among these, the primary cause is the overheating of cooking oils. Despite being considered a stable oil with a high smoke point, palm oil’s acid value (AV) tends to rise under repetitive use or prolonged high-temperature conditions. This accelerates oxidative reactions, subsequently increasing fire risks. Lee et al. [15] reported that after 252 frying cycles with palm oil, the acid value reached the standard limit (0.5 mg KOH/g), confirming that an increased number of frying cycles negatively impacts oxidative stability. Over time, the flash and ignition points of palm oil can decrease, heightening the likelihood of spontaneous combustion under certain conditions. Lee et al. [16] stated that the flash point of cooking oils used for frying is approximately 300–315 °C, the combustion point is around 350–365 °C, and the ignition point is between 390 and 405 °C. However, it also noted the absence of specific fire characteristic values.

The severity of cooking oil fires is exacerbated by their resistance to suppression once ignited. Cooking oils have a small temperature gap between their flash point and ignition point, allowing fires to reignite easily from residual heat even after the heat source is removed [17]. This poses critical safety challenges, not only in domestic settings but also in large-scale food manufacturing facilities. These characteristics highlight the need for fire management strategies that go beyond basic prevention.

The chemical deterioration of palm oil involves oxidative and thermal degradation reactions, during which harmful substances, such as polycyclic aromatic hydrocarbons (PAHs), are produced [18]. PAHs are carcinogenic and mutagenic, posing significant public health risks [19]. Additionally, volatile compounds generated during thermal degradation can disperse into the atmosphere, further increasing the risk of fire incidents [20,21]. The oxidative stability and flash point of palm oil are closely associated with its AV and peroxide value [22]. An increase in the AV reduces the thermal stability of palm oil, thereby raising its fire risk—a concern that necessitates a scientific approach to fire prevention.

These chemical changes degrade food quality and significantly increase the risk of fire accidents. Currently, research in food manufacturing primarily focuses on quality aspects [22,23,24], with limited studies addressing fire-related issues. Systematic studies on the thermal properties and fire risks of edible oils, such as palm oil, are limited. This highlights insufficient preventive measures and educational efforts across industrial, domestic, and commercial settings.

To address these issues, this study aims to provide a comprehensive understanding of the thermal degradation and associated fire risks of palm oil. This study aims to analyze the thermal properties and ignition risks of palm oil samples with varying AVs, providing actionable data to improve the safety of palm oil use in industrial and domestic settings. Additionally, it examines the relationship between changes in AV and fire risk, offering a basis for systematic risk analysis and management in food manufacturing processes.

2. Materials and Methods

This study employed the following experimental procedures and analytical methods: the preparation of palm oil samples, fire reproduction experiments, fire risk characterization tests, and thermal analyses, including Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA).

2.1. Palm Oil Samples and Preparation

The palm oil samples used in this study were provided by Samyang Corporation, a South Korean cooking oil manufacturing company. The physical properties of the palm oil were analyzed as having a melting point of 36.6 °C, a flash point of 314 °C, an ignition point of 315 °C, and a mass purity of 99%. To assess the impact of AV on the oil’s properties, samples were collected after 0, 45, and 90 days of use. For comparative purposes, an additional sample (Sample D) was collected from a high-thermal-stress environment: a frozen food frying batter production process where palm oil was used for 90 days. This process was selected as it subjected the oil to greater thermal stress than snack production processes.

The AVs of the samples were measured using the neutralization titration method in compliance with ISO 660:2009 standards [25]. This method determines the amount of free fatty acids (FFAs) in the oil, which are neutralized by potassium hydroxide (KOH). AV is defined as the milligrams of KOH required to neutralize the FFAs in 1 g of oil. FFAs present in the oil react with KOH, and the consumed quantity of KOH is used to indirectly calculate the FFA content using Equation (1).

$$Acid Value (\mathrm{m}\mathrm{g}/\mathrm{s})=5.611\times (a-b)\times f/S$$

(1)

where $S$is sample weight (g), $a$is the volume of 0.1 N ethanolic KOH solution used for the sample (mL), $b$is the volume of 0.1 N ethanolic KOH solution used for the blank test (mL), and $f$is the factor of the 0.1 N ethanolic KOH solution.

As summarized in

Table 1. Palm oil samples.

Classification	A	B	C	D
Sample	Fresh Oil	Used Oil	Used Oil	Used Oil
Period of use	0 days	1.5 months	3 months	3 months
Acid value	0.02	0.66	1.30	3.98

, the AV increased with longer usage periods, aligning with findings from previous studies [26]. Notably, Sample D, subjected to thermal stress in the frozen food frying batter process, exhibited a relatively higher AV due to contamination and prolonged exposure to high temperatures. This experimental setup was specifically designed to analyze the fire risk characteristics of palm oil, concerning its AV.

This approach enables a systematic assessment of thermal degradation and fire risk factors in palm oil, offering essential data to support the development of safer practices in food processing environments.

2.2. Fire Reproduction Experiment

The fire reproduction experiment was conducted to simulate fire-prone conditions and measure the smoke point and ignition point of palm oil samples. The smoke point is the temperature at which visible smoke first appears from the oil during heating. The ignition point is the minimum temperature at which the oil spontaneously ignites without an external ignition source. This experiment followed the AOCS (American Oil Chemists’ Society) Cc 9a-48 method, utilizing a GL 240 data logger (Graphtec Corporation, Yokohama, Japan) and K-type thermocouples for accurate temperature recording [27].

In this experiment, 100 mL of palm oil was placed in a tin container and heated incrementally using a burner. The temperature at which visible smoke was first observed was recorded as the smoke point, while the temperature at which flames were observed without an external ignition source was recorded as the ignition point. It is important to note that the measured ignition point is not an intrinsic material property and may differ from standardized results obtained using the ASTM E659 [28] method.

To ensure consistency, the experiments were performed under controlled environmental conditions: an ambient temperature of 28 °C, relative humidity of 72.3%, and atmospheric pressure of 1029.7 hPa (1.016 atm). The indoor setting minimized the influence of external factors such as wind.

As the measurements of smoke and ignition points rely on visual observation, there is potential for subjective judgment to influence the results. To address this, a video camera was used to document the moments when smoke and flames appeared, providing objective verification. Additionally, the experiment was repeated three times for each sample, with the lowest recorded value selected to ensure data reliability.

This experimental setup was designed to identify the thermal thresholds at which palm oil transitions from a stable state to a fire-prone condition. The results provide critical insights into the thermal degradation characteristics of palm oil, contributing to a deeper understanding of its fire risk profile under various heating conditions. These findings are essential for enhancing fire safety practices in environments where palm oil is used.

2.3. Fire Risk Characterization Tests

To analyze the fire risk characteristics of palm oil, the flash point and ignition point were measured in relation to the AV. The flash point is defined as the lowest temperature at which oil vapors, when mixed with air, momentarily ignite upon exposure to a small flame near the surface of the sample [29,30]. There are two main methods for measuring the flash point. The closed-cup method involves heating the sample in a sealed environment to prevent vapor diffusion. In contrast, the open-cup method heats the sample in an open environment, allowing vapors to mix with external air. For the same sample, the flash point measured using the open-cup method is typically higher than that measured using the closed-cup method.

In this study, the Cleveland Open Cup (COC) method was employed, as specified in KS M ISO 2592 (2017) [31]. The experimental apparatus used was the Petro Test CLA4 model (Anton Paar). Each test was performed under identical conditions and repeated three times, with the average value of the results adopted as the final measurement. The flash point was calculated using Equation (2), ensuring precision and repeatability. This approach provides critical data for assessing the impact of AV on the thermal and fire risk properties of palm oil.

Table 2. Comparison of flash point testing methods.

Method	Anticipated Flash Point (°C)	Heating Rate	Ignition Source Adjustment Interval (°C)	Precision
				Flash Point (°C)	Repeatability Tolerance (°C)	Reproducibility Tolerance (°C)
Tag Closed Cup	$<$60	$1 °\mathrm{C}/60 \pm$ 6 s	0.5	$0 \le$$\mathrm{x}<$ 13	1.0	3.5
				$13 \le$$\mathrm{x}<$ 60	1.0	2.0
	$\ge$60	$3 °\mathrm{C}/60 \pm$ 6 s	1.0	$60 \le$$\mathrm{x}<$ 93	2.0	3.5
Pensky–Martens Closed Cup	$\le$110	5~6 °C/min	1.0	$\le$104	2.0	4.0
	$>$110		2.0	$>$104	6.0	8.0
Cleveland Open Cup	$\ge$80	$5.5 \pm$0.5 °C/min	2.0	$\ge$80	8.0	16.0

presents the testing methods for determining the flash point according to material properties. Given that the anticipated flash point of the palm oil used in this study exceeds 80 °C, the Cleveland Open Cup method was deemed appropriate and thus utilized.

To calculate the flash point corrected to the standard atmospheric pressure of 101.3 kPa, the following equation is used:

$$F_C=F+0.25(101.3-P)$$

(2)

where $F_C$ is the flash point (°C), $F$ is the measured flash point (°C), and $P$ is the atmospheric pressure during the experiment (kPa).

After obtaining the corrected flash point, the value is rounded to the nearest even number in its final unit. This rounding ensures consistency and adherence to standard reporting formats. Finally, the corrected flash point is expressed in degrees Celsius for practical application and reporting.

This correction process ensures that the reported flash point values are standardized, enabling accurate comparisons across experiments conducted under varying atmospheric conditions.

The mechanism of spontaneous ignition is based on the theory of thermal ignition as described by Daniel A. Crowl and Joseph F. Louvar (2020) [32]. Depending on the type of heat source that increases the material’s temperature, spontaneous ignition can be classified into three categories: spontaneous ignition, autoignition, and pyrophoric ignition. In fire and explosion studies, spontaneous ignition typically refers to autoignition. This occurs when a material ignites at its minimum ignition temperature due to an external heat source.

The autoignition temperature (AIT) is not an intrinsic material property. It is affected by factors such as the sample’s physical and chemical properties, oxygen concentration, container size in the test apparatus, and heating rate. For this study, AIT measurements were conducted in accordance with ASTM E659-15 [28] using a Petro Test ZPA-3 apparatus (Petrotest GmbH, Dahlewitz, Germany ).

Each experiment was performed three times under identical conditions, and the lowest value among the measured results was selected to represent the AIT. The measured data were evaluated to ensure compliance with the maximum allowable deviations for repeatability and reproducibility (as outlined in

Table 3. Allowable deviations for ignition point repeatability and reproducibility.

Observed Ignition Point Range	Maximum Allowable Repeatability Deviation	Maximum Allowable Reproducibility Deviation
$\le 300 °C$	5 °C	10 °C
$>300 °C$	10 °C	20 °C

). To standardize the results, the final AIT values were rounded down to the nearest 5 °C.

This methodology ensures accurate and reliable measurement of AIT, providing a comprehensive understanding of the thermal behavior and fire risk associated with the tested materials under controlled conditions.

2.4. Differential Scaning Calorimeter and Thermogravimetric Analysis

According to the definition of thermal analysis by the International Confederation for Thermal Analysis and Calorimetry (ICTAC), thermal analysis refers to a set of analytical techniques used to measure the physical and chemical characteristics of materials as a function of temperature [33]. The thermal analysis was carried out using DSC and TGA to evaluate the materials’ thermal properties. DSC data were analyzed using STARe Software (version 12.0), while TGA data were processed using Universal Analysis 2000 Software (version 4.5A). These techniques are essential for precisely measuring thermal stability, decomposition characteristics, and thermal transitions, providing critical insights into the properties of the materials.

DSC is a thermal analysis technique that measures the difference in heat flow between a sample and an inert reference material as they are subjected to the same temperature program. This technique allows for the quantitative evaluation of endothermic (heat absorption) and exothermic (heat release) processes. In this study, DSC analysis was conducted in accordance with ASTM E537-20 [34] using a Mettler Toledo DSC 822e instrument (Mettler Toledo Instrument, Greifensee, Switzerland). Samples weighing 10–15 mg were placed in aluminum pans and analyzed over a temperature range of −40 °C to 600 °C, with a heating rate of 10 °C/min. Experiments were conducted under both nitrogen and air atmospheres to compare the thermal decomposition and reactivity of the samples under different conditions. The purge gas flow rate was maintained at 50 mL/min.

The data obtained from DSC analysis were presented in a thermogram, where the x-axis represents temperature and the y-axis represents heat flow. The thermogram can depict heat flow values or be simply labeled with directional arrows, such as ‘Exo’ (exothermic, heat release) or ‘Endo’ (endothermic, heat absorption), along with their corresponding arrows. The thermograms identified three main types of thermal changes: transitions, exothermic reactions, and endothermic processes, which are crucial for understanding the thermal behavior of the materials analyzed in this study.

This comprehensive approach to DSC analysis provides valuable data for assessing the thermal stability and chemical reactivity of the materials under varying environmental conditions [35].

The onset temperature is defined as the temperature at which an exothermic or endothermic reaction begins, marked by the initial deviation of the thermal analysis curve from the baseline. The extrapolated onset temperature is determined by extrapolating the tangent of the exothermic or endothermic graph to intersect the baseline, providing a precise value for the start of the reaction. The peak temperature represents the point at which the reaction rate within a specific interval (S) reaches its maximum. The reaction enthalpy (ΔH), indicating heat absorption (endothermic) or release (exothermic), is calculated using the peak area and the sample’s weight. The peak area is obtained as the product of the x-axis (time, in seconds) and the y-axis (heat flow, in watts, W = J/s), resulting in energy units of joules (J). Dividing the peak area by the sample weight yields the reaction enthalpy per unit weight, expressed as J/g.

TGA is a thermal analysis technique used to measure changes in the mass of a sample as a function of temperature or time. It is used to assess the thermal stability, decomposition characteristics, and oxidative behavior of materials. TGA incrementally increases the temperature at a constant rate, providing insights into the sample’s mass loss and adsorption behavior. This study followed ASTM E1131-20 [36] and utilized the TA TGA 5500 instrument (TA Instruments, New Castle, USA). Samples weighing 5–6 mg were placed in aluminum pans and analyzed within a temperature range of 30–1000 °C, with a heating rate of 10 °C/min. The experiments were conducted under identical atmospheric conditions as those used for the DSC analysis.

The data obtained from TGA are represented as a thermal decomposition curve, with the x-axis indicating temperature and the y-axis showing the percentage of sample weight remaining. This curve depicts the mass loss behavior of the sample and provides critical information on its decomposition [37].

The thermal decomposition curve obtained from TGA can vary significantly depending on the test conditions, particularly the composition of the surrounding atmosphere. The gas environment is one of the most critical factors influencing TGA results. Typically, analyses are conducted in either an inert or an oxidative atmosphere.

In the experiments conducted using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA), high-purity nitrogen gas (purity > 99%) was used as the protective and purge gas. This created an inert atmosphere, preventing oxidation and enabling precise observation of thermal decomposition and physical changes. In such conditions, low-molecular-weight compounds volatilize, high-molecular-weight polymers decompose, and elemental carbon remains stable even above 1000 °C due to the absence of oxygen.

Conversely, air containing approximately 21% oxygen was employed to study oxidative stability and thermal behavior. In this atmosphere, oxygen facilitates the combustion of elemental carbon and accelerates the decomposition of polymers and organic compounds at lower temperatures. This dual-atmosphere approach provided comprehensive insights into material behavior under inert and oxidative conditions.

3. Results and Discussion

3.1. Fire Reproduction Experiment Results

The experimental results for the smoke point and ignition point obtained in this study are summarized in

Table 4. Experimental results of smoke point and ignition point.

Classification	A	B	C	D
Acid Value	0.02	0.66	1.30	3.98
$\mathrm{Smoke} \mathrm{Point} ($°C)	230	190	158	151
$\mathrm{Ignition} \mathrm{Point} ($°C)	317	312	313	304

. The results indicate a clear trend: samples with higher AVs exhibited lower smoke points and ignition points. These findings are consistent with the prior studies of Eom [38] and Jeong [39]. The observed behavior is closely related to the chemical degradation of palm oil caused by the increase in free fatty acids (FFAs) and the formation of oxidative by-products.

The AV is an indicator of the amount of free fatty acids present in oil. A higher AV suggests significant oxidation or decomposition of the oil, resulting in increased levels of FFAs. These chemical changes degrade the thermal stability of the oil, influencing its smoke and ignition characteristics.

The smoke point is the temperature at which smoke begins to appear due to the evaporation of volatile compounds, primarily FFAs and oxidation products, during heating. As the AV increases, the concentration of FFAs rises, which enhances the volatility of the oil. FFAs vaporize more readily at lower temperatures, leading to earlier smoke generation.

The ignition point is the lowest temperature at which oil spontaneously ignites in the air without an external ignition source. The experimental results revealed that oils with higher AVs had lower ignition points. This is attributed to the elevated concentration of FFAs, which promote oxidative reactions. The increased FFA levels result in a chemically unstable structure, making the oil more prone to ignition. FFAs react easily with oxygen, accelerating oxidation and generating heat, which increases the likelihood of ignition. Oxidative by-products further destabilize the oil and create conditions conducive to ignition at lower temperatures.

3.2. Fire Risk Characterization Test Results

The analysis of ignition risks based on the AV yielded results for the flash point and ignition point, as presented in

Table 5. Experimental results of flash point and ignition point.

Classification	A	B	C	D
Acid Value	0.02	0.66	1.30	3.98
$\mathrm{Flash} \mathrm{Point} ($°C)	321	325	321	310
$\mathrm{Ignition} \mathrm{Point} ($°C)	427	428	419	418

. The flash point is a critical indicator for evaluating the safety and fire risk of oils [40]. Experimental results showed that the flash points of samples with low AVs (A, B, C) in the range of 1.3 or below were relatively consistent, ranging from 321 °C to 325 °C, with no significant differences. However, the flash point of sample D, with a high AV of 3.98, was slightly lower at 310 °C. The increase in AV correlates with a higher concentration of free fatty acids, which reduces the oxidative stability of palm oil and increases its susceptibility to oxidation. Despite this, the effect of AV on the flash point was limited in this experiment, and there were no significant differences observed between fresh oil and used oil samples.

The ignition point also plays an essential role in evaluating the combustion characteristics and oxidative stability of palm oil. For samples with low AVs (A, B), the ignition point remained relatively stable, showing no significant changes with increasing AV. However, for sample C, where the AV was moderately increased, the ignition point showed a sharp decline. In the case of sample D, with a very high AV, the ignition point decreased further, though the rate of decline appeared to diminish. This behavior suggests that the ignition point is influenced by complex interactions between the oxidative stability and combustion characteristics of palm oil [41].

3.3. DSC Results

To precisely measure the thermal stability, decomposition characteristics, and thermal transitions of the samples, thermal analysis was conducted based on AV. The results of DSC analysis in nitrogen and air atmospheres are presented in Figure 1. Under air conditions, all samples exhibited exothermic peaks due to oxidative decomposition reactions driven by the presence of oxygen. In contrast, under nitrogen conditions, no significant exothermic peaks were observed for most samples, except for the sample D, with endothermic peaks attributed to evaporation.

Regarding the presence of oxidation reactions, the air atmosphere facilitated oxidative reactions due to the presence of oxygen, making oxidation the dominant reaction pathway. Conversely, in the nitrogen atmosphere, where oxygen was absent, only pure thermal decomposition reactions occurred.

The temperature range differed significantly between the two conditions. In the air atmosphere, the onset temperature was lower, and the reaction range was broader due to the initiation of oxidation reactions. In the nitrogen atmosphere, reactions began at higher temperatures and within narrower ranges, as only thermal decomposition was observed without oxidation.

Thermal stability varied notably between the two atmospheres. In the air atmosphere, oxidation reactions rendered the samples more sensitive to temperature changes, leading to earlier reactions at lower temperatures. In contrast, the absence of oxidation in the nitrogen atmosphere resulted in a higher thermal stability, with reactions initiating at higher temperatures.

The air atmosphere, influenced by oxidation reactions, showed strong energy release and large peaks at lower temperatures, while the nitrogen atmosphere demonstrated thermal decomposition with higher reaction temperatures and lower energy output.

The DSC changes based on AV are summarized in

Table 6. DSC experimental results (air condition).

Samples	${\mathit{T}}_{\mathit{O}} \mathbf{(}\mathbf{°}\mathbf{C}\mathbf{)}$	${\mathit{T}}_{\mathit{E}\mathit{X}} \mathbf{(}\mathbf{°}\mathbf{C}\mathbf{)}$	${\mathit{T}}_{\mathit{P}} \mathbf{(}\mathbf{°}\mathbf{C}\mathbf{)}$	$\mathbf{∆}\mathit{H} \mathbf{(}\mathbf{J}/\mathbf{g}\mathbf{)}$
A	219	-	-	-
	322	338	338	23
	397	428	431	553
	483	-	535	208
B	195	-	-	-
	299	337	340	92
	398	425	428	398
	479	-	552	276
C	197	-	-	-
	295	320	325	48
	427	442	440	823
	481	-	524	284
D	198	-	-	-
	419	428	428	496
	481	-	549	335

$T_O$, Oneset temperature; $T_{EX}$, extrapolation oneset temperature; $T_P$, peak temperature; $∆H$, heat of reaction.

. As the AV increased, both the onset temperature and the peak temperature decreased. This indicates that higher AVs, associated with increased free fatty acid content, led to reduced thermal stability due to enhanced thermal decomposition and oxidation reactions. Consequently, the heat release and reaction intensity increased with a rising AV. These effects were particularly pronounced in the air atmosphere, where oxidative energy release and fire risks were significantly elevated.

3.4. TGA Results

The mass change behaviors of all experimental samples varied significantly between air and nitrogen atmospheres, with samples exhibiting lower decomposition onset temperatures as AV increased. Detailed results are shown in Figure 2 and

Table 7. TGA experimental result.

Condition	Samples	$\mathbf{Decomposition} \mathbf{Temperature} \mathbf{(}\mathbf{°}\mathbf{C}\mathbf{)}$	Mass Change Rate (wt%)
Nitrogen	A	273~470	99.6
	B	245~450/450~685	90.3/8.6
	C	225~450/450~630	91.5/6.9
	D	179~458/458~676	89.5/8.6
Air	A	217~475/475~530	85.7/13.9
	B	193~470/470~515	84/15.1
	C	181~487/487~530	85.2/14.1
	D	180~500/500~530	87.2/11.9

.

The experimental findings indicate that higher AVs correspond to an increased content of free fatty acids (FFAs) in palm oil, which enhances reactivity with oxygen. This heightened reactivity accelerates oxidation reactions, leading to earlier decomposition under air conditions. The influence of AV is particularly pronounced in the air atmosphere, where oxidation reactions reduce activation energy and promote chain reactions, resulting in lower decomposition temperatures. In the nitrogen atmosphere, AV has a limited effect, as the absence of oxygen prevents oxidation reactions.

These results demonstrate that AV plays a critical role in lowering decomposition temperatures under air conditions, where oxidative reactions dominate. As AV increases, the oxidative reactions become more active, making the sample more prone to thermal decomposition and oxidation. This highlights the importance of controlling AV to mitigate the risk of accelerated decomposition and associated hazards, particularly in oxidative environments.

4. Conclusions

The findings demonstrated that an increase in AV elevates the concentrations of free fatty acids (FFAs) and oxidative by-products, thereby reducing the oxidative stability of palm oil. This reduction in stability emerged as a critical factor in lowering the flash point and ignition point of the oil.

Notably, when AV exceeded a certain threshold, the smoke point and ignition temperatures showed a marked decrease. This trend was attributed to the combined effects of chemical degradation and changes in the combustion characteristics of the oil. Thermal analysis further revealed that palm oil with a high AV exhibited accelerated thermal decomposition and oxidation reactions at lower temperatures under air conditions. This behavior was associated with the increased generation of volatile compounds, significantly heightening fire risks.

The study provides empirical evidence linking the chemical changes in palm oil during usage to increased fire risks. It underscores the necessity of setting permissible AV limits, improving temperature control systems, and conducting regular AV monitoring to maintain thermal stability and prevent fires. These findings contribute to strengthening safety in food manufacturing and cooking processes and offer a foundation for developing policies and practical guidelines to mitigate fire incidents.