This work analyzes the results of a group of investigations that were designed with the aim of knowing the characteristics of industrial buildings as well as the impact of thermal overload on aspects such as work productivity, fatigue at the end of the working day. and the resulting thermal stress.
These investigations included industrial and outdoor activities.
Introduction:
The unfavorable effects of hot environments cause loss of motivation for the activity, decreased concentration and attention with the consequent increase in accidents and a decrease in the quality of work and performance that can, according to various authors, decline to 40% 1-2.
The thermal environment can be evaluated through its constituent factors such as: air temperature, air humidity, air speed and radiation temperature. Exposures can be classified into four types, based on the values achieved for the constituent parameters:
Thermal comfort or well-being
permissible limits
critical heat
critical cold
Critical heat environments can cause different pathologies, such as fatigue, heat stroke, hyperpyrexia, dehydration between after. Mondelo3 states that irritability, aggressiveness, distractions, discomfort, reductions in physical and mental performance have also been observed.
These situations under the influence of critical values can even cause death.
Critical heat exposures are more frequent in our country, they can be found in iron and steel, glass factories, construction, fishing and agriculture. For this reason, research has addressed thermal problems with a greater emphasis on hot work.
Currently, with tourism development, it is necessary to also study comfort, since these jobs and even guests require certain micro-climatic conditions. Work on data display screens has been increasing, also requiring more detailed studies 4-5.
When evaluating the microclimate at work, we must bear in mind two fundamental terms: thermal overload and thermal tension.
Thermal overload is nothing more than the amount of heat that has to be dissipated in order for the body to continue in thermal equilibrium and is represented by the sum of metabolic heat (M), and the gains or losses of heat by convection (C) and radiation (R).
The other term corresponds to thermal stress, which is defined as the physiological or pathological modification resulting from thermal overload, for example, increase in pulse, body temperature and sweating.
The physiological and medical consequences are not directly proportional to the intensity of the thermal overload throughout its range. In a rather large temperature range the physiological functions are independent of it.
This happens in the full compensation zone, while in the limited compensation zone the physiological stress increases exponentially, so that for high levels of thermal overload a small increase in it causes a large increase in physiological stress.
The man to stay alive needs to be in constant heat exchange with the environment that surrounds him. For this reason, when talking about life we have to think about heat, since the human body is a constant generator of heat, even in situations of rest it can produce or generate between 65 and 80 w of heat in correspondence with sex, age and the body surface.
The metabolism values can be estimated by tables or in the laboratory through the maximum oxygen consumption or the minute respiratory volume. In Cuba we classify energy expenditure into three categories: light, moderate and heavy.
Not only through metabolism the human body generates heat, when it is exposed to warmer ambient temperatures or higher temperatures than its skin or when it is surrounded by solid objects at higher temperatures, the body will gain heat also in the opposite case (colder temperatures) the body will lose heat. Here the mechanisms of thermal exchange come into play (metabolism, convection, radiation and evaporation) through which thermal exchanges between the human body and the environment will be carried out throughout the life of the human being, that is it is a constant movement of energy, that if it disappeared, so would life itself and therefore society.
Niebel1 states that the body temperature of the worker must be taken into account, so the cumulative effects of all heat receiving sources must be determined. Both thermal equilibrium and thermal overload situations between man and his environment can be expressed by:
M ± R ± CE = A
Where:
M = heat gain by metabolism
R = heat exchange by radiation
C = convection heat exchange
E = heat loss through evaporation
A = heat stored in the body
4.Indicators used to assess the work microclimate.
To assess thermal overload, different indicators have been proposed and used, among which we must mention that they are the most widely used internationally and in our country, the Effective Temperature Index which was applied since 1923, the Corrected Effective Temperature Index (1946), the Caloric Overload Index (1955) and the Wet Bulb Globe Temperature Index (1957).
In our country the Cuban standard 19 01 03 «Air of the Work Zone6 was used for several years. This standard is based on independent parameters such as: air temperature, relative air humidity and balloon temperature, with the consequent limitation This implies in the interpretation of it. In this norm, three micro climatic conditions are proposed: optimal permissible and critical; therefore, it is necessary to highlight that for the classification of the optimal conditions, the evaluation of several indicators was considered, among them the skin temperature with which the use of the Fanger7 expression was proposed to determine the desirable values of the microclimate.
The remaining micro climatic conditions were classified according to criteria of the international literature and the subjective responses of the individuals studied, not being supported by measurements of the physiological responses.
We are currently working with the Wet Bulb Globe Temperature Index which has been recognized and recommended by the International Organization for Standization (ISO) 8. In this regard, Mondelo points out the following: advantages: 1) It allows the evaluation of the environment by means of a unique value that integrates all the parameters of the microclimate, 2) requires simple equipment for evaluation, which can be built in the country, 3) the calculation method is extremely easy, 4) can be used for the evaluation of hot indoor and outdoor environments, 5) allows its weighting for variable levels of exposure. As a disadvantage it has the following:
1) not recommended for very dry environments (relative humidity less than 30% and
2) not recommended for situations close to comfort.
Impact of thermal overload on Cuban workers
In Cuba for a part of the time, unfavorable weather conditions no longer cause difficulties for heat removal, but they also impose an additional load on the body due to convective heat and radiation heat, which adds to or adds to the caloric load derived from technological process, often turning workplaces »as undesirable». This leads to a marked decrease in labor productivity, high absenteeism, instability of the work force and a greater number of accidents.
For this reason, it is necessary to solve with the planned and gradual improvement of the micro climatic conditions and with the elaboration every time of better factory projects. This question concerns the hygienists at work, but also in equal measure to designers of the Ministry of Construction, to the teaching staff of the Higher Education of undergraduate and postgraduate courses in which engineers, architects and doctors are prepared to face the solution to these problems.
But for the above to be achieved, scientifically based bases and principles are needed, which show the most effective and at the same time economic solutions to solve this problem in our country, in order to achieve a real improvement in the micro-climatic working conditions that satisfy our workers. This must go hand in hand with a substantial saving in the installation and operation of ventilation systems, which, as we know at present, are not very efficient and cause waste of energy, mainly because the designers do not have information on the behavior of the microclimate in our industries and they lack recommendations adapted to our conditions.Another aspect of savings is the one that would be produced by decreasing or eliminating the payment for abnormal working conditions in terms of heat.
To find out about these problems, a group of investigations was started on industrial buildings in Cuba and their influence on the working microclimate9-13. The behavior of the microclimatic variables, the use of natural ventilation, compliance with the Cuban norm, and an analysis of the roofs, among others, were studied.
In these investigations it was observed that the ships studied had little air movement (almost null), in most of the workstations.
It was observed that there were a large number of closed windows for various reasons (very unrelated to the production process), which reduced the possibility of air renewal inside the premises through natural ventilation. The reduction in the utilization coefficients of natural breezes was also observed due to the existence of nearby buildings.
Buildings or warehouses with five different types of roofs were studied: asbestos cement, galvanized steel sheets, galvanized steel sheets with sandwich-type thermal insulation, precast double T-type concrete slabs and finally, precast siporex slabs.
The ships that had decks with less thermal resistance and struts equal to or less than 6 meters turned out to have worse micro-climatic conditions, so it was advised that given the need to use such struts, the possibility of increasing the thermal resistance of the decks should be analyzed. Considering the results obtained, a methodological guide is being prepared for designers and engineers who are involved in the development of industrial projects.
It should be clarified that these studies were carried out in warehouses or industrial buildings with cold technology, that is, that large sources of radiant heat were not generated due to the technological process. The appreciable radiant heat load was due to the incidence of sunlight only.
For the study of thermal overload, workers have been studied who work in textile garment workshops14, spinning workshops15-16, construction17, oil stoves18 and glass combined19 among others.
In these investigations the behavior of other aspects such as work productivity, fatigue at the end of the working day, exposure time and thermal tension were studied through the variables oral temperature, skin temperature, heart rate and hourly sweating rate.
Below are some highly synthesized results of the research referred to above.
To find out the behavior of work productivity and fatigue at the end of the working day, an investigation was carried out in a workshop for male textile garments with thirteen workers. In this study, no significant differences were found in work productivity, but nevertheless fatigue at the end of the day was significant since a greater number of fatigued persons were found in the second days of each situation studied, this is typical considering the residual effect of the day. above (tables 1 and 2).
An investigation that was part of the Main Medicine Problem on "The Cuban Working Woman" corresponded to the research topic: the assessment of thermal overload in working women. 15 workers were selected from a spinning workshop, they remained in a biped position and walking during the work day.
Table 3 expresses the results of the physiological variables studied in this research such as energy expenditure (GE), heart rate (HR), oral temperature (TO), skin temperature (TP) and the rate of Hourly sweating (TSH). An increase was observed in hot conditions. This activity was classified from the energy point of view as light since the values of energy expenditure are below 176W.
The heart rate had an increase in hot conditions because the increase in thermal overload increases the accumulation of heat in the body and this imposes a greater load on the circulatory system that is felt through the increase in heart rate; if these average values obtained are compared with the values proposed by the American Heart Association for rest (from 50 to 100 in / min.) and the limit recommended by the World Health Organization of 110 in / min. This activity can be classified from the cardiovascular point of view as light. The oral temperature did not show alarming values either, since if the criterion of adding 0.4 ° C to the obtained value is considered, at no time does the recommended value of 38.0 ° C be exceeded.
The skin temperature showed values that agree with the values proposed by Fanger7, Minard20-21, Landberg and other authors to maintain thermal comfort and thermal balance.
The hourly sweating rate had an increase in hot conditions, but the values found are lower than those set by the World Health Organization (between 1.5 and 2 liters / hour).
From all of the above, it will be evident that the workers who work in similar situations of metabolic activity and thermal overload will not present a thermal tension that can cause serious pathologies, thermal equilibrium will be reached but with signs of discomfort and discomfort in hot situations (Table 3).
For several years the Main Medicine Problem was executed on construction workers. Nine activities were selected to study the thermal overload in activities in this sector: digging with a pick, digging with a shovel, laying floor slabs, stowage, formwork, trolley, mixing, plastering the wall and putting blocks in different micro-climatic conditions (winter and summer).
Despite finding high heart rate values in some activities (digging with shovels and digging with picks) the results showed the absence of an alarming thermal tension maintained since the workers regulated their work and rest time, which facilitated their physiological recovery (tables 4 and 5).
Due to the high radiant temperatures caused by oil stoves and the large number of these in the country, a study was carried out in food processing centers of three hospitals in Havana, to find out the exposure time, the values of the temperature of the skin and the response time of painful sensation due to the effect of radiation. Eight chefs were selected for this. The radiation temperature values reached values of up to 58.9 ° C, the contact temperatures in the kitchens in the front area were 92 ° C and on the sides 93 ° C and 126 ° C respectively. These values exceed the internationally recommended 40 ° C limit.
Exposure in this type of work is not continuous, the response of painful sensation on the skin by the effect of thermal radiation, manifests itself in cooks for a maximum tolerable exposure of no more than 7 minutes. The average values of the skin temperature did not present relevant values since they are within the limits with which the thermal equilibrium is maintained (tables 6 and 7).
Another physiological-environmental study corresponded to that carried out on workers in the glass industry. The appearance of fatigue at the end of the working day was assessed using a battery of five tests. Ten workers including blowers, molders, punches and cutters operating at high temperatures, in chain production regime, were studied by recording the pulse, oral temperature and sweating. Daily averages were obtained that were contrasted with the results of the fatigue tests. These were negative on all occasions, except for the Yoshitake test, which was positive in eight of the ten workers.
The perception of fatigue that this implies is justified by the monotony of the task and the adverse conditions of the microclimate. The negative results of the rest of the tests correspond to slight changes in the physiological parameters (all within the safety zone) during work activity, despite the micro-climatic values above the established norm (Table 8).
IV. Conclusions
According to the findings of these investigations, it can be affirmed that the most widespread pathology is fatigue. The diseases described in the specialized literature do not appear due to several factors, among which we can point out, firstly, the work and rest regime that in in many cases it is regulated and in others it is not, which implies a physiological recovery of the workers, it is also necessary to consider the degree of acclimatization that the Cuban accustomed to living with high temperatures all year has and to a certain extent the decrease in the rate of activity by the worker when he feels the effects of heat. Reason why we can infer that Cuban workers maintain thermal equilibrium in the performance of their activities.
It has been determined that the use of additional measures such as the ingestion of liquids and salts that facilitate the acclimatization process in light and moderate work and up to 35.0 ° C air temperature is unnecessary, since the Cuban worker develops a process of natural acclimatization that conditions the physiological basis necessary to achieve an immediate adaptation to climatic conditions in the industry, which are generally less humid and allow the main mechanism of heat dissipation, sweat evaporation to take place quickly and efficient22.
Notwithstanding the foregoing, it is necessary firstly to apply control measures to solve this risk that is very present in industries and secondly, to achieve a comfortable, hygienic and safe working environment for the man who works in the production process and a high quality of safety and protection of facilities and the environment.
Bibliography.
1. Benjamin W. Niebel. Industrial engineering. Methods, times and movements. Alfaomega Editions, Mexico, 1992.
2. David J. Oborne. Ergonomics in Action: The adaptation of the working environment to man. 2nd edition. México, Trillas, 1990.
3. Pedro Mondelo et al. Ergonomics 2. Comfort and thermal stress. Mutual Universal. Ediciones UPC, Barcelona, Spain, 1996.
4. Suárez CR, Padilla MC, García NO, Barrios AM: Some ergonomic aspects in the use of data display screens. Rev Cubana.Hig Epidemiol 34 (2): 124, July December, 1996.
5. Mondelo P et al. Ergonomics 1. Foundations. UPC editions, January 2003
6. Cuba. State Committee for Standardization. System of Labor Protection and Hygiene Standards. Air from the Work Zone. General sanitary hygienic requirements.nc 19 01 03, Havana, 1980.
7. Fanger, PO: Calculation of Thermal Comfort: Introduction of the Basic Comfort Ecuation. ASHRAE Trans, Vol II N ° 73.1967.
8. International Organization for standization. ISO 7243.Hot Environments Estimation of the heat stress on working man, based on the WBGT index (Wet Bulb Globe Temperature), 1989.
9. Díaz, Abreu A, Padilla MC, Macías MJ: Edificaciones Industriales y Microclima laboral I. Behavior of climatic variables. Rev Ing Ind. Vol XIII, 3, 27,1992.
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11. ------- Industrial Buildings and Labor Microclimate III
Compliance with the Cuban Standard Rev. Ing Ind Vol XIV, 1, 25,1993.
12.------– Industrial Buildings and Labor Microclimate IV. Prediction of microclimatic variables. Rev Ing Ind Vol XIV, 1, 37,1993.
13. ------- Industrial Buildings and Labor Microclimate V. Analysis of the roofs. Rev Ing Ind Vol XIV, 3,, 1993.
14. Padilla Méndez, C., et al: Productivity and Microclimate in workers in a textile manufacturing workshop. Rev Ing Ind Vol. X, No. 2.87 1989.
15.: Work and Thermal Overload in Working Women. An experience in a spinning workshop. Rev Ing Ind. Vol XII, No. 3.33, 1991.
16.: Productivity, sensation and feelings of heat in a workshop of spinning Rev Ing Ind Vol XIII, N ° 1,23,1992.
17.: Thermal Overload and its effects on workers in three construction activities. Rev Ing Ind, Vol XV, N ° 3,63,1994.
18. Wilford Lamelas E., et al.: Evaluation and control of the heat that originate from the nationally manufactured oil stoves. Bulletin of Occupational Medicine Vol 2,3,179, 1986.
19. Ponmerenck, Carlos, W., et al: Physiological criteria for the regulation of work in thermal overload. Light work. Cuban Rev. Hig. Epidemiol 22 (1): 13 26, Cuba, 1984.
20. Minard, MD: Physiology of heat stress he Industrial Environments its Evaluation and Control, NIOSH, USA, 1974.
21. National Institute for Occupational Safety and Health. Criteria for a Recommended Standard. Occupational exposure to hot environments. Revised criteria, 1986
22. Wong. Kwan, C. Physiological criteria of acclimatization to heat.
Work to opt for the title of First Degree Specialist in Occupational Medicine. Institute of Occupational Medicine 1983.
Table 1: Increases in labor productivity and proportion of rejections in women workers in the textile industry.
| Employee # | Productivity increase (%) | Rejections with air conditioning | Rejections without air conditioning |
| one | -twenty | 16 | 14 |
| two | -9 | one | one |
| 3 | -13 | 1.5 | 0 |
| 4 | 22 | 0 | 0 |
| 5 | -27 | 0 | 13.4 |
| 6 | fifteen | 0 | one |
| 7 | 5 | 5 | 3 |
| 8 | -10 | 5 | 3 |
| 9 | fifteen | 10 | 4 |
| 10 | twenty | 6 | 5 |
| eleven | 7 | 3 | 3 |
| 12 | 7 | 0.5 | 4.3 |
| 13 | -42 | 0 | 1.3 |
Table 2: Number of fatigued
| Yoshitake test
1 st day 2 do day |
Critical melting frequency
1 st day 2 do day |
|||
| Air conditioning | 10 | eleven | two | 3 |
| No air conditioning | 12 | 13 | 7 | 8 |
Table 3: Average values and standard deviations of the physiological variables in two microclimatic situations in spinning workshops.
| With air conditioner | No air conditioning | |||
| Variables | X | S | x | s |
| Energy expenditure (GE) | 137.1 | 37.1 | 148.9 | 31.6 |
| Heart rate
(Fc) |
90.4 | 11.8 | 96.9 | 13.0 |
| Oral temperature
(To) |
36.9 | 0.2 | 37.1 | 0.1 |
| Skin temperature
(Tp) |
32.7 | 0.8 | 34.4 | 0.7 |
| Hourly sweating rate
(TSH) |
70.0 | 46.5 | 200.5 | 52.1 |
| GE: Watt Fc: lat / min To: ° C Tp: ° C TSH: ml / h |
Table 4: Differences in HR at rest and activity in the winter period.
| Exercise | Fc rep | Fc act | diff |
| Digging with shovel | 67.5 | 108.8 | 41.3 |
| Repel wall | 70.3 | 88.4 | 18.1 |
| Formwork | 67.5 | 89.0 | 17.5 |
| Wander | 73.9 | 107.2 | 33.3 |
| Make mix | 77.6 | 100.3 | 22.7 |
| Dig with pick | 79.0 | 119.6 | 40.6 |
Table 5: Differences in heart rate at rest and activity in the summer period.
| Exercise | Fc rep | Fc act | Dif |
| Digging with shovel | 74.0 | 122.0 | 48.0 |
| Repel wall | 72.4 | 86.0 | 14.0 |
| Wander | 66.6 | 93.7 | 13.6 |
| Make mix | 70.6 | 102.6 | 7.1 |
| Dig with pick |
86.0 |
129.4 | 43.0 |
| Stow | 72.0 | 92.84 | 20.8 |
| Laying floor tiles | 68.9 | 87.5 | 18.5 |
Table 6.Average values of climatic variables in the workplace versus kitchens.
| Dry air temperature ° C | 26.6 | 33.3 | 34.1 |
| Radiation temperature ° C | 29.9 | 56.5 | 58.9 |
| Relative humidity% | 71.0 | 56.0 | 49.0 |
| Start of the day | Intermediate of the day | End of the day |
Table 7: Average values of the skin temperature of the cooks studied.
Centers |
Start day |
Intermediate |
End of the day |
| Hospital 1 | 31.3 | 34.4 | 34.9 |
| Hospital 2 | 31.7 | 34.5 | 34.9 |
| Hospital 3 | 30.5 | 34.7 | 34.6 |
| Averages | 31.1 | 34.5 | 34.8 |
Table 8: Values of the physiological variables studied in workers in the glass industry.
| Exercise | HR (lat / min) | To (° C) | TSH (ml / h) |
| Blower | 85.0 | 37.0 | 333.0 |
| Molder | 97.0 | 37.1 | 236.0 |
| Punch | 88.0 | 36.8 | 230.0 |
| Cutter | 69.0 | 36.9 | 186.0 |
