Assessment of Indoor Air Quality in Small and Medium Food Industries and Effects towards Perceived IAQ Symptoms

Abstract

Background: Cooking activities generate pollutants that can cause adverse health effects to occupants. This study aims to characterize the indoor air environment in small and medium food enterprises (SMEs), as studies in this area are scarce. Methods: A series of field measurements were conducted to investigate the IAQ at 14 SMEs selected in Pulau Pinang for three different cooking methods (frying, boiling, and baking). Data on environmental perception and health symptoms were obtained from 76 workers by using a validated questionnaire. Boosted regression tree (BRT) analysis and parametric tests were performed to evaluate the impact of the IAQ on the prevalence of disease symptoms. Results: The results showed that CO₂, temperature, and relative humidity were higher than the standard limits, while PM_2.5 and TVOC were below the standard limits. Using BRT analysis, CO₂ was indicated as the highest pollutant to cause complaints by workers (41.55%), followed by CO (21.93%), relative humidity (11.81%), temperature (10.66%), PM_2.5 (7.07%), and TVOC (6.99%). This study indicated that workers in SMEs food industries are affected by the indoor air quality at their workplace in which CO₂ was the main parameter influencing their health. This study suggests that future research focuses on boiling and frying SMEs with CO₂, CO, temperature, and relative humidity to be afforded emphasis.

1. Introduction

Indoor air quality (IAQ) has been one of the most significant environmental problems worldwide due to the impact on building occupants [1,2]. Concentrations of pollutants are often two to five times higher in the indoor environment than the outdoor environment, which exposes occupants to greater effects [3]. This problem worsens when indoor activities emit pollutants and cannot be withdrawn from the indoor space [4]. Despite this fact, many studies have focused on outdoor pollutant trends, while a lack of information is found on indoor trends [1]. For example, IAQ studies have been carried out extensively in homes, schools, hospitals, commercial buildings, and office buildings. However, there is very little study found on the workplace, such as small and medium industries, especially food sectors, whenever this industry is known to support the economy, locally, or internationally. IAQ has become an important health and safety concern in workplaces [4]. Yet, SMEs have received very low attention from authorities, especially regarding the aspects of safety and health as compared to bigger industries [5].

Commonly, indoor air pollutants include carbon monoxide (CO), volatile organic compounds (VOC), particulate matter, and carbon dioxide (CO₂) [6,7]. These pollutants are generated from many factors, including cooking activities that affect the temperature and humidity level in the indoor environment [6,7,8]. Several other sources are also related to poor IAQ, including methods of cooking, frequency, type of cooking devices, type of fuel, type of oil used for frying and ventilation factors that affect the IAQ in a building [2,9,10,11,12,13,14,15].

This study on IAQ in small and medium food enterprises (SMEs) should provide a better understanding of the real situation occurring in the industry, allowing preventive measures to further be taken. This study focuses on assessing the quality of the indoor environment from the measurement of IAQ parameters, including fine particles, carbon dioxide, carbon monoxide, total volatile organic compounds, and temperature, as well as relative humidity in SME food production areas where cooking is conducted. Furthermore, the effects on the health and comfort of the workers were measured using perceived IAQ symptoms reported by workers using a questionnaire survey.

2. Materials and Methods

2.1. Study Area and Population

This study was conducted at small and medium food enterprises conducting cooking activities located in Pulau Pinang, as shown in Figure 1. It is a cross-sectional, comparative study carried out in fourteen SMEs selected from food industries that conduct cooking activities in their food processing. There was a total of 341 SME food enterprises in Pulau Pinang in reference to SME Corp Sdn. Bhd with 200 SMEs were conducting cooking activities in their work processes. Out of the 200 SMEs, only 145 SMEs are still active, and others were permanently closed. In this study, fourteen SMEs (10%) were selected using stratified random sampling from the four districts in Penang, which are the North Seberang Perai District, Central Seberang Perai District, South Seberang Perai District, and Penang Island. This design allowed each SME an equal chance of selection. The SME food industries were selected based on three types of cooking methods: frying, boiling, and baking. SMEs that were conducting cooking activities performing frying, boiling, or steaming and baking in their production areas were first sorted and selected randomly. The selected SMEs were then coded from A to N. A total of five frying SMEs, four boiling SMEs, and five baking SMEs were involved in the study. A comparison of the concentration of IAQ parameters following cooking methods and the effects on health towards the workers explained IAQ issues in the workplace.

2.2. Data Collection

The IAQ measured in the study includes PM_2.5, CO₂, CO, TVOC, temperature, and relative humidity. IAQ monitoring was performed using two portable indoor air quality monitors: Quest EVM-7 and IQ-610 Gray Wolf. EVM-7 was used to measure PM_2.5 at the study locations, while IAQ probe IQ-610 Gray Wolf was used to measure temperature, relative humidity, carbon dioxide, total volatile organic compounds, and carbon monoxide. Two-to-three consecutive days were taken to measure the IAQ in the study locations following the size of the processing areas where the average readings on eight-hour working time were taken. The two pieces of equipment were set to measure the IAQ parameters within five-minute intervals. The measurements of IAQ parameters were carried out following guidelines from the Industry Code of Practice on Indoor Air Quality (ICOP-IAQ) 2010 by the Department of Safety and Health, Malaysia. Sampling was carried out within a sampling area at least 0.5 m from the corners or windows, walls, partitions, and from other vertical surfaces. The sampling was carried out at least one meter away from localized sources and one and a half meters above the ground following the guideline.

2.3. Questionnaire

To assess the perceived IAQ symptoms among the respondents, a standardized questionnaire for workplaces was used. The questionnaire (MM 040 EA) was developed by the Department of Occupational and Environmental Medicine, which is valid, clear, and reliable [16]. There were four sections available in the questionnaire regarding the psychosocial climate: the work environment, work conditions, past or present diseases or symptoms, and present symptoms. Only workers who worked in the production areas were selected to participate in the questionnaire survey. All workers working in the production area were included in the study, as they shared the same breathing zone. Workers who worked in areas besides production areas were excluded from the study. No exclusion was made for the status of smoking due to small number of workers in production areas. Workers who spent 20 h or more per week of their time at the workplace were eligible to participate in the study to ensure adequate and meaningful exposure to the indoor environment [17]. The total workers who worked in the production areas were 118. All respondents were interviewed so that the maximum response rate could be obtained. The full response rate was obtained at SME H and SME N (100%), while the lowest response rate was at SME M with 43.48%, with a less than 50% response rate. The total response rate for fourteen SME was 64.41%.

Table 1. The number of respondents involved in the survey.

SME	Total Respondents	Total Response	Percentage of Response (%)
A	4	3	75.00
B	4	3	75.00
C	5	3	60.00
D	13	7	53.85
E	3	2	66.67
F	11	7	63.64
G	10	8	80.00
H	4	4	100.00
I	15	9	60.00
J	10	8	80.00
K	8	5	62.5
L	4	3	75.00
M	23	10	43.48
N	4	4	100.00
Total	118	76	64.41

shows the number of respondents involved in the survey with the percentage of response rate received.

2.4. Statistical Methods

Statistical Package for Social Sciences (SPSS) version 25.0 was used to analyze the results. Descriptive statistics using mean, standard deviations (SD), range, minimum, and maximum were used to determine the concentration of IAQ parameters at the three different cooking SMEs.

2.4.1. Boosted Regression Tree Analysis

Boosted regression tree (BRT) analysis was used to identify the relative influence of indoor air parameters on the IAQ perceived symptoms, which determined the most significant parameters to impose adverse health effects on the respondents. The measures are based on the number of times a variable is selected for splitting, weighted by the squared improvement to the model as a result of each split, and averaged over all trees [18]. BRT analysis incorporates important advantages of tree-based methods, handling different types of predictor variables, and accommodating missing data, which does not need prior data transformation or elimination of outliers. This analysis can fit complex nonlinear relationships and automatically handle interaction effects between predictors.

2.4.2. Fisher’s Exact Test

Fisher’s exact test was used to study the associations between cooking methods and the prevalence of perceived IAQ symptoms among workers. This test is suitable for use in assessing whether two categorical variables are related. Fisher’s exact test was used due to low expected frequencies. Exact significant of p-value < 0.05 shows the positive correlation between variables.

2.5. Ethical Consideration

This research was approved by UiTM Research Ethics Committee with reference number REC/435/18.

3. Results

3.1. Demographic Information

Table 2. Demographic Data.

Parameter	Frying a n (%)	Boiling b n (%)	Baking c n (%)
Age
18–30	9 (50.0%)	13 (46.4%)	16 (53.3%)
31–40	6 (33.3%)	3 (10.7%)	7 (23.3%)
41–50	3 (16.7%)	6 (21.4%)	3 (10.0%)
>60	0 (0.0%)	6 (21.4%)	4 (13.3%)
Gender
Male	2 (11.1%)	13 (46.4%)	11 (36.7%)
Female	16 (88.9%)	15 (53.6%)	19 (63.3%)
Smoking status
Yes	0 (0.0%)	6 (21.4%)	2 (6.7%)
No	18 (100.0%)	22 (78.6%)	28 (93.3%)

^a n = number of respondents (18); ^b n = number of respondents (28); ^c n = number of respondents (30).

shows the demographic data of the respondents. A greater proportion of respondents were in the age group of eighteen to thirty years old across the three SMEs’ cooking methods with frying, boiling, and baking being 50.0%, 46.4%, and 53.3%. Most of the respondents were female, and most of the respondents were nonsmokers. In frying SMEs, all workers did not smoke (100%), while in boiling and baking SMEs, 21.4% and 6.7% were nonsmokers, respectively. There were no allergic diseases, and no asthma, hay fever, or eczema among the respondents, and these symptoms are not shown in the table.

3.2. The Concentration Level of Indoor Air Parameters (PM_2.5, CO₂, CO, TVOC, Temperature, and RH) at Three Different Cooking SME Food Industries

Table 3. Statistical summary of IAQ parameters in three different cooking methods at SME food industries.

Parameters	Description	Frying SMEs	Boiling SMEs	Baking SMEs	IAQ Standard
PM2.5	Mean	70.21	33.18	30.17	3000 μg/m3
	SD	131.03	38.48	23.59
	Range	1624	380	181
	Max	1626	381	183
	Min	2	1	2
CO2	Mean	981.31	1495.19	1148.85	1000 ppm
	SD	175.92	772.62	419.39
	Range	1025	3153	2197
	Max	1645	3839	2765
	Min	620	686	568
CO	Mean	2.17	7.87	5.43	9 ppm
	SD	5.75	18.45	12.12
	Range	68.4	105.2	104.9
	Max	68.4	105.2	105.2
	Min	0	0	0.3
TVOC	Mean	0.59	0.90	0.64	3 ppm
	SD	0.22	0.72	0.10
	Range	1.39	3.57	0.77
	Max	1.55	3.77	1.21
	Min	0.16	0.2	0.44

shows the mean concentration of IAQ parameters recorded of three different cooking methods at SME food industries following the mean, SD, range, minimum, and maximum readings. The mean concentrations of PM_2.5 levels were identified below the threshold limit value of 3000 μg/m³ by the American Conference of Government Industrial Hygienists (ACGIH) at all study locations. The highest mean concentration was the highest in frying SMEs with 70.21 μg/m³. The maximum and minimum value of the concentrations examined were 1626 μg/m³ and 2 μg/m³, respectively. The concentration of PM_2.5 at frying SMEs was about double the concentrations from boiling and baking SME food industries. The mean concentration of PM_2.5 at boiling and baking food SMEs were 33.18 μg/m³ and 30.17 μg/m³, respectively. The concentration range of PM_2.5 were 1624 μg/m³, 380 μg/m³, and 181 μg/m³ for frying, boiling, and baking, respectively.

CO₂ was highest in boiling food SMEs (1495.15 ppm), followed by baking food SMEs (1148.85 ppm) and frying food SMEs (981.31 ppm). The high level of CO₂ may be due to type of fuel. Fuel types such as LPG were used in seven SMEs (SME A,B,C,D,E,F, and G); a combination of LPG and electric were used in SME I, J, and L; diesel was only used in SME H; electricity was used in SMEs K and N; and a combination of electricity and diesel were used in SME M. It was found that SMEs that used a gas stove used LPG as cooking fuel, while those that used an electric stove used electricity as cooking fuel. The use of fuel types varied according to the food processes.

CO concentration was below the standard limit of ASHRAE 9 ppm, where boiling food SMEs recorded the highest concentration level with 7.87 (±18.45) ppm. Frying food SMEs recorded the lowest CO mean concentration with 2.17 (±5.75) ppm. The mean concentration of TVOC emitted at boiling food SMEs was the highest with 0.90 (±0.72) ppm. The concentration of TVOC exceeded the standard of 3 ppm only at the maximum value of boiling food SMEs. The range of TVOC at boiling food SMEs recorded at 3.57 ppm, which was much higher than the other two types of SME. Frying and baking food SMEs, however, did not show a high level of TVOC concentrations.

The range standard of temperature should not be more than 30 °C, as implied by the ACGIH. However, the mean temperature levels recorded exceeded the standard range at all SMEs, as shown in Figure 2. Mean RH was observed to exceed the standard of 30–65% at frying and boiling food SMEs with 67.72% and 73.53%, respectively. However, baking food SMEs were also shown to almost exceed the standard by a mean reading of 64.33%, with the highest range and maximum reading observed at the SMEs at 43.3% and 87.7%, respectively, as shown in Figure 3. Note that the different colors of box plots in Figure 2 and Figure 3 indicating the SMEs food industries involved in the study from SME A until SME N. Violations of standards were found at concentration levels of CO₂, temperature, and relative humidity in all three types of cooking SMEs except for PM_2.5, CO, and TVOC.

3.3. Complaints Related to Work Environment

Table 4. Complaints Related to Work Environment at SME with Three Different Cooking Methods.

Work Environment	Frying SMEs (n = 18)	Boiling SMEs (n = 28)	Baking SMEs (n = 30)
	%	%	%
Draught	77.8	64.3	80.0
Room temperature too high	100.0	100.0	100.0
Varying room temperature	27.8	53.6	23.3
Room temperature too low	0.0	0.0	0.0
Stuffy bad air	100.0	100.0	100.0
Dry air	55.6	75.0	80.0
Unpleasant odor	27.8	10.7	0.0
Static electricity	0.0	0.0	0.0
Passive smoking	0.0	0.0	0.0
Noise	0.0	0.0	0.0
Dim light or glare	0.0	0.0	0.0
Dust or dirt	100.0	100.0	100.0

shows the percentage of respondents’ complaints regarding the work environment at their workplaces. From the result, the most common complaints were the room temperature being too high; stuffy, bad air; and dust and dirt with all types of SME recording 100% complaints. Complaints on draught were also recorded as high with baking SMEs being recorded as highest (80%), followed by frying SMEs (77.8%), and boiling SMEs (64.3%). Dry air was seen as highest at baking SMEs (80%), followed by boiling SMEs (75%) and frying SMEs (55.6%). An unpleasant odor was recorded in frying SMEs (27.8%) and boiling SME (10.7%) and none in baking SMEs. No complaints were found on room temperature being too low, static electricity, passive smoking, noise, or dim light or glare.

3.4. Perceived IAQ Symptoms among Respondents

Table 5. Perceived IAQ symptoms among respondents.

Symptoms	Frying SMEs (n = 18)	Boiling SMEs (n = 28)	Baking SMEs (n = 30)
	%	%	%
Fatigue	61.1	42.8	30.0
Heavy-headed sensation	77.8	35.7	20.0
Headache	66.7	17.8	16.7
Nausea and dizziness	5.6	0.0	0.0
Difficulty in concentrating	0.0	7.2	0.0
Eye problem	27.8	0.0	0.0
Nasal problem	22.2	3.6	0.0
Dry throat	22.2	10.7	43.4
Cough	5.6	3.6	20.0
Dry or flushed facial skin	22.2	14.3	20.0
Scaling/itching scalp or ears	61.1	17.9	22.2
Dry hands	16.7	3.6	0
Other	38.9	35.7	23.3

shows the feedback on perceived IAQ symptoms among respondents in the SME food industries. The feedback of symptoms was taken into consideration using “yes” and “no” answers. Heavy headache was found to be the most prominent IAQ symptom among respondents in frying SME food sectors at 77.8%, followed by the second-highest symptom of headache at 66.7%, fatigue at 61.1%, scaling/itching scalp or ears at 61.1%, and other symptoms being lower than 30%. In boiling food SMEs, the highest symptoms were fatigue (42.8%), followed by a heavy-headed sensation (35.7%), and other symptoms (35.7%). Baking food SMEs were observed to have the lowest number of symptoms, with the highest reported being a hoarse and dry throat (43.4%) and fatigue (30%). Five symptoms were not experienced by the respondents in baking food SMEs compared to frying and boiling food SMEs. Difficulties in concentrating were observed in boiling food SMEs (7.2%), while there were none in frying and baking food SMEs. Nausea and dizziness (5.6%) and eye problems (27.8%) were also observed in frying food SMEs, while there were none in boiling and baking food SMEs.

3.5. Associations between Indoor Air Parameters (PM_2.5, CO, CO₂, TVOC, Temperature, and RH) with Perceived IAQ Symptoms among SME Workers

BRT analysis was used to predict the continuous predictor variables of indoor air parameters on the response variables, which are the perceived IAQ symptoms. The BRT analysis comparison was conducted using the root mean squared error for prediction (IAQ parameters) and the relative influence on the mean of the symptom’s variable value in percentage. Overall, the values ranged from 6.99% to 41.55%. Figure 4 shows the graph of the contribution of the indoor air parameters with the relative influence, which reflected the total score symptoms among respondents. The results indicated that CO₂ contributed to the highest perceived IAQ symptoms at about 41.55%, followed by CO at 21.93%, relative humidity at 11.81%, temperature at 10.66%, PM_2.5 at 7.07%, and TVOC at 6.99%. Note that different colors of the bar chart in the figure indicating the different types of indoor air parameters measured in the study.

The results in

Table 6. Fisher’s exact test between symptoms and cooking methods.

Perceived IAQ Symptoms	Frying SMEs	Boiling SMEs	Baking SMEs	p-Value
	n	n	n
Fatigue	11	12	9	0.117
Heavy-headed sensation	13	7	5	<0.05
Headache	11	5	5	<0.03
Nausea and dizziness	1	0	0	0.237
Difficulty in concentrating	0	2	0	0.186
Eye problem	5	0	0	<0.05
Nasal problem	4	1	0	<0.05
Hoarse, dry throat	4	3	13	<0.02
Cough	1	1	6	0.09
Dry or flushed facial skin	4	4	4	0.72
Scaling/itching scalp or ears	11	5	6	<0.05
Dry hands	3	1	0	<0.04
Other	6	10	8	0.77

indicated that there were associations (p-value < 0.05) between cooking methods with the symptoms of feeling heavy headache, headache, eye problems, nasal problems, hoarse/dry throat, scaling/itching scalp or ears, and dry hands. On the other hand, no significant correlation was identified between the perceived IAQ symptoms of fatigue, nausea, dizziness, difficulties concentrating, cough, dry/flushed facial skin, dry hands/itching/red skin, and other symptoms with different types of SME cooking methods.

Figure 5 clearly shows the pattern of significant perceived IAQ symptoms among the respondents following the cooking methods. Although boiling food SMEs had the highest level of pollutant concentration (Table 3) and level of relative humidity (Figure 3), the perceived IAQ symptoms, however, were highest in frying food SMEs.

4. Discussion

This study was able to identify the effects of different cooking methods on indoor air quality in SME food enterprises. Cooking activities of frying, boiling, and baking generate different levels of pollutants in the indoor environment and affects temperature and relative humidity levels. As smoking among workers was not observed during the study, cooking is likely to be the primary source of indoor air pollution in SME food industries. Cooking stuffs, styles, and fuels were said to affect the nature and concentration of pollutants [14,15,19]. Therefore, it can be said that the situation of IAQ in SME food enterprises in Malaysia is in an unsatisfactory condition. The study indicates some violation of parameters regarding baseline standard limits, including the violation of CO₂, temperature, and relative humidity. In an IAQ assessment, having any studied specified air pollutants exceeding the limit of exposure is considered unsatisfactory [20]. This study indicated problems of IAQ parameters of the three parameters while CO, PM_2.5, and TVOC were still within safe limit ranges.

Different cooking methods significantly contributed to the buildup of nuisance and hazardous pollution [15]. This study found that boiling food SMEs have greater IAQ parameters than frying and baking food SMEs. This observation might be due to the fact that the mean concentrations and levels of four of the six parameters studied were higher in boiling food SMEs, including CO₂, temperature, and relative humidity. CO₂ concentration is one of the parameters to be considered in assessing indoor air quality in a building. Because CO₂ is often used as an alternate measure of ventilation rate, this study took CO₂ as one of the indoor air pollutants emitted by the cooking process. A study on commercial kitchens identified the same issues regarding CO₂ concentration, which exceeded standards due to cooking activities [4]. It was indicated in the study that CO₂ in SME food enterprises is one of the major issues that need to be tackled. CO₂ was found to contribute to the highest perceived IAQ symptoms among workers. Poor IAQ often causes complaints on associated symptoms [21]. A high concentration of CO₂ causes complaints among workers with symptoms that include headaches, drowsiness, difficulty concentrating, increased respiration rate, eye and throat irritation, sinus and chest tightness, and wheezing [16,22]. Short-term exposure to CO₂ at concentrations of 1000 ppm can also affect cognitive performance such as decision-making and problem resolution [22]. Ventilation factors and other relevant factors such as frequency of cooking and applications of hood or exhaust fans could also affect the concentration of the pollutant [2,10,23]. These factors should be determined in the next study. It was also found that temperature levels and relative humidity in all SMEs are at a critical alarm level for violation of standards, indicating an urge for the implementation of corrective measures. IAQ symptoms among respondents were also affected by the high temperature and relative humidity in the SMEs. This is because high temperature and relative humidity contributes to poor IAQ, which causes major discomfort among occupants [24]. Temperature and relative humidity caused a heavy-headed sensation; headache and fatigue; eye, nose, and throat irritation; discomfort; difficulty in concentrating; and dry skin [14,16,25]. Cooking activities such as either frying, boiling, or baking generate high indoor temperatures. A high relative humidity in boiling food industries indicates that cooking using water affects the water content in the air.

This study indicated that CO concentration did not exceed the standard limit, which was below 9 ppm. CO poisoning, even at lower concentrations, due to cooking appliances is known to cause neurological symptoms and increase other health risks [26]. In this study, CO was the second parameter associated with perceived IAQ symptom after CO₂. Our findings indicated that the presence of CO in the workplace could cause health effects to workers. CO due to the incomplete combustion of carbon-containing fuels can cause poisoning, where the symptoms include chest tightness, headache, fatigue, dizziness, drowsiness, and/or nausea [26]. In this study, CO concentration was found to be higher in boiling SMEs than frying and baking SMEs with a mean concentration reading of 7.87 ppm reaching the standard limit. This finding was supported by Wang et al., who identified that boiling food produced higher CO than other cooking methods such as frying [8]. In contradiction to other authors, frying was indicated to produce greater CO than boiling [2,10,14,23]. However, high-fat food from boiling activities could produce higher CO than frying [23]. Comparison with small-scale food industries cannot be made, as many have focused on residential and commercial cooking. A study has suggested that CO be used as an indicator for PM_2.5 in which higher CO shows higher PM indoors [14]. However, it was argued that those pollutants’ concentrations may be different following setting and should be measured separately [6]. PM_2.5 was recorded at 7.07% of perceived IAQ symptoms among the respondents. The IAQ symptoms related to PM_2.5 include shortness of breath, eye and lung irritation, nausea, fatigue, stuffy nose, light-headedness, and possible allergy aggravations [27]. Although the concentration was below the safe range, frying SMEs indicated a higher concentration of PM_2.5 than the other two cooking methods. This is because cooking with oil produces more particles than boiling and steaming [2,12]. Frying activities in small-scale food industries might not be a major issue; however, the effects of continuous exposure to workers need to be studied. This study did not associate CO and PM_2.5. However, future studies could observe the relationship between the two parameters because they are emitted during cooking activities and cause health problems. Different types of stoves also affect the level of PM_2.5, CO, and CO₂ indoors, where gas stoves emit higher pollutants than electric stoves, and kerosene stoves emitted higher pollutants than gas stoves [2,12]. The current study, however, did not identify the issue from the type of stoves, and purposive sampling on the determinants is recommended in the next study.

The mean concentrations of TVOC were identified below the standard limit. However, TVOC concentration had a range of 3.57 ppm above ACGIH standard in boiling SMEs, which can pose health threats to workers. Exposure to TVOC from 0.05 to 0.80 ppm can cause possible irritation and discomfort while exposure to 0.80 to 6.64 ppm can cause serious health symptoms and discomfort [7]. Kabir and Kim, in their study, identified that the frying method produced higher VOCs than boiling, which differs from this study’s findings [15]. Although TVOC caused the least perceived IAQ symptoms among respondents, further investigation is needed to properly identify the TVOC problem from cooking activities in food SMEs, especially at the SMEs that emitted a higher TVOC concentration.

Proper ventilation rates to exhaust pollutants from the building can lower health effects on workers, in addition to improving temperature and humidity indoors [4,6,16,21,27,28,29]. Thus, further study on ventilation effectiveness is required to identify the issues in SME food enterprises so that corrective actions can be taken. This study serves as baseline data for future research on IAQ in SME food sectors. This study has managed to confirm that cooking activities such as frying, boiling, and baking emit pollutants to the environment and cause IAQ symptoms in workers. In addition to cooking methods, type of fuels, room arrangement, outdoor filtration, combustion devices, ventilation, and building materials influence the emission of pollutants [10,12,23]. Future studies on IAQ in SME food enterprises should measure all these determinants so that comprehensive measures can be taken to improve IAQ in SMEs and to protect the health and safety of workers.

5. Conclusions

In conclusion, different cooking methods in SME food enterprises affect the concentration of indoor air parameters with major problems of high concentration of CO₂, temperature, and relative humidity. Furthermore, workers at SME food industries were affected by the IAQ parameters at their workplace, especially CO₂, which was determined as the most likely parameter to influence the perception of IAQ symptoms. Therefore, it is prudent for the improvements of indoor air quality in SME food enterprises to be made a major focus by the authorities to ensure that the exposure of indoor air pollutants, temperature, and relative humidity towards workers can be prevented.

IAQ assessment and monitoring by the authorities should be carried out in SME food enterprises, which presently seems to be neglected. Focus should be emphasized on the process of ventilation, including existence of special hoods or ducting in cooking areas, as well as suitable building structures and cooking areas. Legislators need to formulate legislation for indoor air for small and medium food enterprises, especially those who conduct cooking activities, to create a safe and comfortable workplace.