
































Microsoft Word - 72. Evaluation of Heat Stress on Bakery Worker in Makurdi Benue State, North East Nigeria


     American Journal of Agricultural Science, Engineering and Technology 
 

 
 

 ISSN: 2158-8104 (Online), 2164-0920 (Print), 2021, Vol. 5, Issue.2 
http://journals.e-palli.org 

 



     American Journal of Agricultural Science, Engineering and Technology 
 

 
 

 ISSN: 2158-8104 (Online), 2164-0920 (Print), 2021, Vol. 5, Issue.2 
http://journals.e-palli.org 

The American Journal of Agricultural Science, Engineering and Technology (AJASET) is 
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     American Journal of Agricultural Science, Engineering and Technology 
 

 
 

 ISSN: 2158-8104 (Online), 2164-0920 (Print), 2021, Vol. 5, Issue.2 
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EDITORIAL BOARD 

 

Chief Editor 

Dr Mamun-Or-Rashid 

Professor, Dhaka University, Bangladesh 

 

Board Members  

Dr. Sumit Garg, IL, USA 

Professor Dr. James J. Riley, The University of Arizona, USA 

Dr. Ekkehard KÜRSCHNER, Agriculture Development Consultant, Germany 

Professor Dr. Rodriguez Hilda, USA 

Professor Dr. Michael D. Whitt, USA 

Professor Dr. Wael Al-aghbari, Yemen 

Professor Dr. Muhammad Farhad Howladar, Bangladesh 

Dr. Clement Kiprotich Kiptum, University of Eldoret, Kenya 

Professor Dr M Shamim Kaiser, Professor, Jahangirnagar University, Bangladesh 

Professor Dr Mohammad Shahadat Hossain, Chittagong University, Bangladesh 

 

Managing Editor 

Md. Roshidul Hasan 

Professor, Department of Computer Science and Information Technology,  
Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh



     American Journal of Agricultural Science, Engineering and Technology 
 

 
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EVALUATION OF HEAT STRESS ON BAKERY WORKER IN MAKURDI BENUE 

STATE, NORTH EAST NIGERIA 

Amine, J. D.1, Owhor Sampson Chisa2* and Orafa Patience Nguseer3 

DOI: https://doi.org/10.5281/zenodo.5372151  

ABSTRACT 

Nigeria being a tropical nation with high temperature and some Nigerian bakeries use mud 

oven which expose workers to direct contact with heat increasing their risk of heat stress. 

This research work tends to evaluate heat stress on bakery workers in Makurdi, Benue State. 

Forty questionnaires were validly filled and handed in from the workers at the various 

bakeries. Data such as age, duration of exposure as well as heat stress estimation and 

satisfaction level were filled in and data were analysis using statistics and results shows that 

heat stress reduces efficiency and productivity in workers poses health risk in workers such as 

heat cramps, heat rashes and in severe cases even heat stroke which may threaten the life of 

these workers. The results from measurements in this work has shown that bakery workers in 

Makurdi metropolis are highly exposed to heat stress and are likely to experience one 

disorder or the other with possible death consequences. It was also found that heat stress is 

often an overlooked problem as most workers lacked proper knowledge of control measures 

and employers have made little or no effort to prevent heat stress disorders. 

Keywords: Bakery workers, Heat exposure, Heat stress, Oven, Temperature index, Wet bulb 

globe. 

1 Department of Mechanical Engineering, Federal University of Agriculture Makurdi, Benue 

State, Nigeria, +234(0)7039239777, https://orcid.org/0000-0003-0867-2779 
2 Department of Mechanical Engineering, Federal University Wukari, Taraba state, Nigeria, 

+234(0)8064344429, https://orcid.org/0000-0003-2126-7903 
3 Department of Food Science and Technology, Federal University Wukari, Taraba state, 

Nigeria, +234(0)7066936137, https://orcid.org/0000-0003-2378-5405 
*Corresponding Author: (Email: owhorchisa@gmail.com) 

 

 

 

 

 

INTRODUCTION 



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Heat is a form of energy characterized by an increase or a decrease in temperature, Heat may 

be defined as energy in transit from a high temperature object to a lower temperature object. 

Stress can be defined as the brain's response to any demand. Heat stress occurs when the 

body’s means of controlling its internal temperature starts to fail. Air temperature, work rate, 

humidity and work clothing are all factors which can cause heat stress. Climate in the work 

environment is an important factor in determining the physical comfort satisfaction of 

workers, and their comfort affects job satisfaction and performance. There are four primary 

variables that define climate, namely air temperature, humidity (relative humidity), air 

movement and radiation from surrounding objects including the sun. Environmental 

conditions cause body temperatures to rise above or fall below normal, there is a risk of either 

heat stress or cold stress. Nigeria being a tropical nation with high temperature and some 

Nigerian bakeries use mud oven which expose workers to direct contact with heat increasing 

their risk of heat stress. Heat stress reduces efficiency and productivity in workers poses 

health risk in workers such as heat cramps, heat rashes and in severe cases even heat stroke 

which may threaten the life of these workers. This research work is to establish the inherent 

heat stress amongst bakery workers and proffer solutions or suggestions to mitigate them. 

This work will help employers and owners of bakery to be more conscious of their workers’ 

health and see ways to improve the conditions of their facility to reduce heat stress. It would 

also create awareness amongst workers to be mindful of their state of health as they work in 

high heat intensity facilities. It would also help engineers look at ways to create or remodel 

bakery facilities and equipment’s in order to reduce the temperature around the working areas 

in bakeries thereby reducing heat stress. 

 

LITERATURE REVIEW 

The art of baking was brought into Nigeria by some freed Negroes who were well established 

as independent artisans in various trades. These Negroes educated and Christianized settled 

first in Lagos where baking was carried out in their homes until about 1900. Then, 

commercial bakeshops began to spring up. The eating of bread which was the main baked 

product at that time disseminated first along the coastline (Ports) Warri, Calabar, Port-

Harcourt, and then inland Onitsha etc. The continued growth of the bakery industry 

necessitated the establishment of flour mill in Nigeria by the Nigerian government. A baker is 

a worker who mixes flour, salt, yeasts, spices, sugar, and other ingredients to prepare dough, 

batter, fillings, etc., which are then formed into bread, cakes, rolls, etc., and baked in an oven. 

Their work environment is an important determinant of health; it can influence health 



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positively or negatively, and for most people, work is essential for economic, social as well as 

physical wellbeing. 

Occupational heat exposure is of rising concern globally with climate change drawing more 

consideration to this issue. Whether in outdoor or indoor situations, working in excessive heat 

environments (temperatures exceeding 35° Celsius) poses risks to workers’ health and 

reduces labor productivity. Excessive heat exposure creates an occupational hazard of high 

concern, particularly in indoor and outdoor workplaces lacking effective climate control. It 

has been estimated that roughly 20% of the workforce hours in South East Asia were lost as a 

result of heat exposure. Projections for the year 2030 estimate a loss of around 70 million 

work life- years in labor productivity due to heat exposure and a loss of 880 000 work-life-

years due to occupational heat stroke mortality, in indoor and outdoor workplaces. 

Occupational health researchers have focused on heat stress in outdoor workers in the field of 

agriculture, construction, farming, and fishing, who are particularly vulnerable due to 

constant exposure to heat, especially in hot or humid weather conditions. Indoor workers are 

also at risk if temperatures in their work environment are poorly regulated. The Occupational 

Health and Safety Administration (OSHA) has identified indoor industries at risk of 

experiencing heat related illnesses due to the presence of heat-generating appliances; these 

include bakeries, kitchens, laundries, and furnaces. Further research is needed to quantify the 

risk of heat exposure and heat-related illnesses among indoor workers in various professions, 

including bakery workers. In addition to measurements of indoor temperatures, additional 

assessments are needed, such as personal factors and work tasks that may impact risks 

associated with indoor heat exposure. 

Heat stress experienced in hot working environments occurs when the body temperature 

exceeds 38°C, resulting in health symptoms, such as dry skin, chills, high body temperature, 

confusion, dizziness, fainting, fatigue, weakness, nausea, and muscle cramps. Other heat 

stress-related health conditions include heat stroke, heat exhaustion, heat syncope, and heat 

cramps. In addition, extreme heat has been associated with mental health effects. A 

systematic review conducted in 2018 shows evidence of a positive relationship between heat 

exposure and occupational injuries, mainly caused by fatigue, reduced psychomotor 

performance, loss of concentration, and reduced alertness. Despite the risks posed by heat 

stress, work systems have increasingly encouraged workers to ignore symptoms of heat-

related illnesses, to maintain the work pace and avoid breaks and work interruptions. 

Temperatures and humidity in indoor work environments may increase during hot and humid 

seasons, especially in workplaces that lack adequate ventilation or air conditioning. The 



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presence of drinking water and emergency procedures are also factors affecting workers’ 

responses to heat exposure. Risk factors for heat stress include individual susceptibility, such 

as age and gender, along with workers’ hydration levels, workplace and environment 

temperature levels, and work rate and activities. Moreover, the effects of hot and humid 

working conditions may exacerbate if workers are unaware of heat-related illnesses and their 

prevention. The management of heat-related occupational exposures must involve risk 

assessment and control measures at the level of the work, the workers, and the work 

environment. However, regulations in low and middle-income countries (LMIC) are 

challenged by socioeconomic factors and lack of adequate infrastructure, frameworks, and 

technical expertise. 

Moreover, the tasks performed in bakeries subject workers to high levels of heat exposure 

resulting in health impacts if not properly controlled. Most of the literature on bakery workers 

have focused on industrialized bakeries studying the respiratory effects of exposure to flour 

dust or skin irritation and allergies. Other publications have also studied and assessed 

ergonomic hazards, mainly musculoskeletal disorders, and mental and self-rated health 

among bakery workers. Few studies exploring heat exposure among bakery workers 

documented elevated heat stress exposures among those workers. Research has also 

distinguished the working conditions and risks between traditional bakeries and industrialized 

bakeries. A recent study showed that workers in traditional bakeries are exposed to higher 

levels of heat stress when compared to workers in industrial bakeries. In addition, the 

incidence of heat stress among bakery workers in traditional bakeries has been shown to be 

3.3% higher than those in industrial bakeries. 

 

MATERIALS AND METHOD 

 

Heat stress checklist 

An initial survey was carried out in each of the bakeries with the help of the heat stress 

checklist to ascertain their working condition. Each parameter is given a risk score and a brief 

description to help understand the score. The parameters that influences heat stress such as air 

temperature, radiant temperature, air velocity, humidity, clothing and metabolic rate were 

carefully observed as then given a risk score on the checklist according to how it is described 

by the checklist. 

 

Questionnaires  



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The questionnaire was divided into 3 sections. Section A required that participants indicate 

their demographic information including their age, sex, job description. Section B assessed 

their work environment by asking participant to give information about how long they have 

been working in the bakery, how long they work and their shifts as well as their perception of 

the thermal environment and how much it affects them. Section C asked about experienced 

heat disorder and how often as well as if they have any form of education on heat stress and 

preventive measures. 

 

Measurements of environmental parameters 

Measurement was taken using a certified ADARSH wet bulb and dry bulb thermometer. 

Measurement was taken during 10:00am and 2:00pm when most bakeries usually start the 

actual baking process. The hygrometer was first recalibrated, and then measurement was 

taken at three levels, above the head, at chest and below the waist level and the average was 

calculated.  

Air temperature measurement was gotten reading the dry bulb thermometer and Relative 

humidity is determined by finding the differences in degrees between the dry-bulb and wet-

bulb readings on the horizontal scale at the top, and then reading off where this column 

intersects the horizontal row containing the dry-bulb temperature reading on a hygrometric 

chart. 

 

Conversion tables 

To determine the level of heat stress an operator is subjected to, an approximation conversion 

table by U.S Bureau of Meteorology was used in determining the WBGT. This table does not 

take the variation in the intensity of solar radiation or of wind speed into account, and assures 

a moderately high radiation level in light wind conditions. 

WBGT = 0.567 × Ta + 0.393 × e + 3.94.................................(1) 

where: 

Ta= Dry bulb temperature (°C) 

e= Water vapour pressure (hPa) [humidity] 

 

𝒆 =
𝒓𝒉

𝟏𝟎𝟎
× 𝟔. 𝟏𝟎𝟓𝑬𝒙𝒑

𝟏𝟕.𝟐𝟕𝑻𝒂

𝟐𝟑𝟕.𝟕 𝑻𝒂
…………………………………………........ (2) 

Where rh = relative humidity (%) 



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The conversion table makes use of temperature and relative humidity to determine the 

WBGT. The wet bulb temperature, dry bulb temperature and relative humidity for the work 

environment were measured and used on the table to identify the prevailing WBGT. From 

IS0 7243, heat stress occurs when WBGT≥31˚C. 

 

 

Figure 1: Conversion table (source: U.S bureau of meteorology) 

Statistical analysis 

Data received from the field was analyzed using Excel 2007 (Analysis Tool Pack) to test the 

hypothesis. With the help of MINITAB statistical software package, mean & standard 

deviation, & coefficient of co-relation were used for statistical analysis.  

 

RESULTS 

This research was conducted in ten bakeries of which two used the traditional mud oven and 

eight used electrically powered oven in carrying out their work. Forty workers filled out 

questionnaires about their psychological description of their working conditions as well as 

other details. This is the results of the various methods used to conduct this research.  

 

Heat stress checklist 

The Mean Score of the Heat Stress Factors (Parameters) using Heat Risk Assessment 

Checklist is as shown in table 1 and 2. 



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Questionnaire and observation 

Forty questionnaires were validly filled and handed in from the workers at the various 

bakeries. Data such as age, duration of exposure as well as heat stress estimation and 

satisfaction level were filled in. Table 3 shows that the participants are from all age group 

while Table 4 shows the duration which they have worked in the bakery. Table 5 gives us the 

psychological description given by the workers of the heat stress they are faced with and 

Table 6 tells us how much the heat stress affects their task in terms of their job satisfaction. 

Table 7 is derived from personal observation of the relevant positions available in the bakery 

that are in risk of heat stress It was observed that most bakeries where this research was 

conducted had no personal protective clothing or heat-conserving clothing. Rather, they 

either wear light clothing or are half-naked. 

 

Measurements of environmental parameters 

Two major hot rooms were identified at the bakery and these are (1) the furnace – which 

seemed to be an open space housing the oven and in some cases also the generator. This is 

where baking is actually carried out (2) the kneader – this is a closed room, this is where 

mixing, milling and pounding takes place before it is kept to rise and subsequently sent to be 

baked. Relative humidity and air temperature were measured as used to calculate the heat 

load the bakery workers are subjected to. The computed result is shown in tables 8 and 9. 

 

Table 1: Age distribution of participants 

Age Number of workers Percentage 

11-20 3 7.5% 

21-30 25 62.5% 

31-40 10 25.0% 

41-50 2 5.0% 

Total 40  

 

 

 

 

 

 



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Table 2: Experience on the job 

Number of workers Duration 

4 Below 1 year 

16 1 – 5 years 

11 6 – 10 years 

7 11 – 15 years 

2 16 – 20 years 

 

Table 3: workers heat level rating 

Heat level description Workers Percentage 

5 3 7.5% 

4 13 32.5% 

3 23 57.5% 

2 1 2.5% 

1 0 0.0% 

Total 40  

 

Table 4: Heat level satisfaction 

Satisfaction level Workers Percentages 

5 0 0.0% 

4 9 22.5% 

3 17 42.5% 

2 11 27.5% 

1 0 0.0% 

Total 40  

 

Table 5: Tasks and their estimated metabolic work rate 

Job description Metabolic work rate (Wm-2) 

At the furnace 130 

Milling 100 

Pounding 110 

Mixing 120 



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Table 6: Heat stress at the furnace 

Bakery Heat 

source 

Air 

temperature 

Relative 

humidity 

Heat stress 

furnace 

Exposure Source of 

ventilation 

A Electric 

oven 

35.5˚C 66 39.00 5hrs Open air 

B Electric 

oven 

35.5˚C 63 38.33 4hrs Open air 

C Mud oven 36.0˚C 69 40.40 10hrs Open air 

D Electric 

oven 

34.4˚C 66 37.50 7hrs Open air 

E Electric 

oven 

36.0˚C 63 39.00 10hrs Open air 

F Electric 

oven 

34.5˚C 66 37.63 5hrs Open air 

G Electric 

oven5 

36.0˚C 50 35.98 5hrs Open air 

H Mud oven 32˚C 60 33.26 3hrs Open air 

I Electric 

oven 

34.4˚C 66 37.50 8hrs Open air 

J Electric 

oven 

35.5˚C 62 38.10 5hrs Open air 

 

Table 7: heat stress at the kneader 

Bakery Air 

temperature 

(˚C) 

Relative 

humidity 

Heat 

stress at 

kneader 

working 

hours 

Source 

of heat 

Ventilation 

A 36.5 66 40.41 6hrs miller none 

B 36 67 39.93 7hrs miller none 

C 38 68 43.12 6hrs miller none 

D 36 69 40.40 7hrs miller none 

E 36.5 66 40.41 6hrs miller none 

F 35 68 38.75 6hrs miller none 



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G 37.5 63 41.10 7hrs miller none 

H 34 62 36.13 4hrs miller none 

I 36 69 40.40 8hrs miller none 

J 37 64 40.64 6hrs miller none 

 

Statistical analysis 

Table 8: Descriptive statistics table 

 Air 

temperature 

(oven) 

˚C 

Air 

temperature 

(kneader) ˚C 

Relative 

humidity 

(oven) 

Relative 

humidity 

(kneader) 

Heat 

stress 

index 

(oven) 

Heat stress 

index 

(kneader) 

N 10 10 10 10 10 10 

Min 32 38 50 62 33.26 36.13 

Max 36 34 69 69 40.40 43.12 

Mean 34.98 36.25 63.1 66.2 37.67 40.13 

S.D. 1.23450 1.16070 5.27994 2.48551 1.94293 1.77602 

 

Table 9: Analysis of variance for WBGT (kneader) 

Source of 

Variation 

Sum of 

Square 

Degree of 

Freedom 

Mean Square Fcal F tab 

Between Groups 16.9874 9 1.887489 0.078832 3.020383 

Within Groups 239.4319 10 23.94319   

Total 256.4193 19    

 

Table 10: Analysis of variance for WBGT (oven) 

Source of Variation Sum of 

Square 

Degree of 

Freedom 

Mean Square Fcal F tab 

Between Groups 14.19404 9 1.577116 0.036602 3.020383 

Within Groups 430.8873 10 43.08873   

Total 445.0813 19    

 

 



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DISCUSSION 

Table 1. shows the different age groups workers belong to but the maximum number of 

workers are in the age group of 21-30 & 31-40 (total 87.5 %.). Age is one of the important 

when considering heat stress especially in determining heat strain. The older a person is the 

more likely they are to suffer from the effect of heat; Particular consideration should be given 

to individuals over 45 years of age. It is not advisable to post persons over 50 years of age for 

strenuous jobs in hot environment. But 2% of workers were in the age group of 41-50 years 

working in hot environment. For these employees there is a need to monitor the body core 

temperature, heart rate, rest pause etc. at workplace. However, there is a definite decline in 

maximal work capacity with age. The fall in maximal cardiac output with age probably 

contributes to reduced work capacity and greater susceptibility to heat injury as well. 

From table 2, most workers (90%) have spent over a year at their job and the 10% have spent 

more than 3 weeks, hence could also be said to be acclimatized. Before acclimatizing to 

working under hot conditions as well as returning during breaks from duty, participants 

reported cases of illnesses as well as symptoms of heat stress. Illnesses were ranging from 

minor fever to rare cases of yellow fever, while symptoms of heat stress such as fatigue, heat 

rash, headaches, heat cramps seemed to occur on daily basis or periodically as the case may 

be. Although no worker had a medically reportable case or severe symptoms of heat illness 

which caused them to cease work, their symptoms indicated that the physiological systems of 

the body were struggling to meet the demands of thermoregulation. Therefore, the primary 

avenue for reducing heat illness symptoms arising from this program of research is to 

improve the workers’ hydration status and a point worth noting is that none of these bakeries 

had a well-organized system providing water for workers, most of the workers had to buy 

their own during break time which increases risk factor. 

Table 4 shows the assessment of the workers’ heat rating during the baking task obtained 

from data collected through questionnaires. 97.5% of the respondents complained of feeling 

hot during the frying process, of which 40% rated the heat level as very high, and were 

exposed to this level of heat for a minimum of four hours.  

Table 5 shows that while most are uncomfortable with the heat level, it doesn’t have much 

effect to their job attesting to the fact that they are acclimatized to the working conditions. 

Table 6 The values measured and calculated show that those at the kneader have a higher risk 

factor than those working at the oven. This is very unlikely hypothetically, since standing 



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nearer to the oven sends direct heat to the worker but this was the case in bakeries visited due 

to 2 reasons. First, the oven is located in an open space with access to open air for ventilation 

while the kneader is a roomy space with very few windows for ventilation. This was said to 

be needed to help the bread rise faster. Secondly the kneader has an additional heat load 

coming from the milling machine as well as it was over populated.  

Table 7 Few workers worked at the oven compared to the millers, mixers as well as the 

pounders who work at the kneader resulting in higher temperature as well as higher humidity. 

This gives an average of 38mins for those working in the oven and 29mins for those working 

at the kneader which implies that anything further than this could cause serious discomfort 

and increase risk factor. According to interviews as well as reports, all bakery workers work 

more than the tolerance time with some working more than six hours with a 1hr – 2hr break. 

Table 8 Statistically, using the Pearson’s correlation test, Pearson’s correlation coefficient (r) 

between heat stress index at the oven and ambient temperature in the oven is 0.789. Pearson’s 

coefficient between the heat stress index at the kneader and its ambient temperature is 0.949. 

This is high relative to the Pearson’s correlation coefficient between heat stress index at the 

oven and kneader and their respective relative humidity which is 0.585 and 0.421 at the oven 

and kneader respectively. This shows that air temperature has a higher significant value on 

heat stress as a rise in temperature would also increase heat stress. Relative humidity is not so 

significant call it depends on other factors such as water vapor pressure and air velocity.  

Table 9 No significant difference between heat stress at the oven and heat stress at the 

kneader was found (p>0.05). Also relationship between air temperature and relative humidity 

is not statistically significant (p>0.05) showing that one variable does not cause the other i.e. 

a rise in temperature does not necessarily mean a rise in relative humidity. The mean 

temperature of heat stress at oven and at kneader is significantly different from the required 

mean (p<0.05).  

Also, statistically significant difference was seen between WBGT average of furnace in all 

bakeries (p<0.01). This issue is because of difference in bakery equipment’s and varying 

weather conditions during which this research was carried out. 

The result of the hypothesis test using ANOVA in Table 9 and 10 indicates that there is a 

significant difference between the indices for different workstations at Fcal < Ftab. 

Ho: the period (work station) the measurements were taken had no significant effect on the 

values collected (results obtained). 



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Hi: the period (work station) the measurements were taken had significant effect on the value 

(results obtained). 

Decision: Accept H0, if Ftab< Fcal, that is, the treatment has no effect on the parameter of 

interest. Hence Hi is rejected; Accept H1 if Ftab > Fcal, that is, there is significant difference in 

the treatment with respect to the parameter of interest. Hence H0 is rejected. 

The Null hypothesis is, therefore, accepted. This implies that there was no significant 

difference in the treatment and method used in measuring the WBGT between the different 

bakeries. 

Hence all analysis used to indicate that there is evidence of heat hazard in bakery. 

 

CONCLUSIONS 

Heat stress disorders are gentle killer diseases and must not be overlooked by those 

concerned in any industrial environment. In a very warm weathers like Nigeria, the concern 

for heat stress becomes much more stringent and should be seriously monitored. The results 

from measurements in this work has shown that bakery workers in Makurdi metropolis are 

highly exposed to heat stress and are likely to experience one disorder or the other with 

possible death consequences. It was also found that heat stress is often an overlooked 

problem as most workers lacked proper knowledge of control measures and employers have 

made little or no effort to prevent heat stress disorders. Further research on heat effect of heat 

stress (Heat strain) on bakery workers is highly recommended. 

 

REFERENCES 

Afshari D, Moradi S, Ahmadi Angali K, Shirali G-A. (2019). Estimation of heat stress and 

maximum acceptable work time based on physiological and environmental response 

in hot-dry climate: a case study in traditional bakers. Int J Occup Environ 

Med.;10(4):194-202. 

Arbury S, Jacklitsch B, Farquah O, (2014). Heat illness and death among workers – United 

States, 2012–2013. MMWR Morb Mortal Wkly Rep.;63(31):661-680. 

Baleshti MH. (2015). Evaluating the potential risk of musculoskeletal disorders among 

bakers according to LUBA and ACGIH-HAL indices. J Occup Heal 

Epidemiol.;3(2):72-80. 



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