Principles of assessment

 

THERMONEUTRAL ENVIRONMENT

The index for determining the thermal sensation of a human in a given environment is the Predicted Mean Vote (PMV) index. Using the PMV index, the average thermal sensation of a large group of people subjected to a specific combination of variable environmental parameters is predicted. [in Polish: Sobolewski, A., Zwolińska, M. O problemach związanych z oceną środowiska cieplnego za pomocą wskaźnika PMV Bezpieczeństwo Pracy: nauka i praktyka 2011 nr 12  20-23; PN-EN ISO 7730:2006. Ergonomia środowiska termicznego – Analityczne wyznaczanie i interpretacja komfortu termicznego z zastosowaniem obliczania wskaźników PMV i PPD oraz kryteriów lokalnego komfortu termicznego (oryg).]

 

 

 

gdzie:

ADu – DuBois’s surface (area of ​​the human body), m2

QM – metabolic heat, W

η – physical fitness of the body

pw – partial water vapour pressure (in the air), mmHg

tw – air temperature, °C

fcl – the ratio of the area of ​​the body covered by clothing to the area of ​​the exposed body

tcl – average temperature of the human body surface covered with clothing, °C

Tmrt – average radiation temperature, °C

αk – coefficient of heat transfer by convection, W/m2K.

 

The Predicted Percentage of Dissatisfied (PPD) index specifies the expected percentage of dissatisfied people. [PN-EN ISO 7730:2006. Ergonomics of the thermal environment -- Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria]

 

PPD = 100 - 95exp(-0,03353PMV4 - 0,2179PMV2)

 

After the assessment or measurement of the above factors, it is possible to predict human thermal sensations, expressed in a 7-point scale of thermal sensations, as: hot (+3), warm (+2), slightly warm (+1), neutral (0), slightly cool (-1), cool (-2), cold (-3) by calculating the PMV and PPD indexes. [Fanger PO: Thermal comfort. Warsaw, Arkady 1974; ASHRAE Handbook - HVAC Systems and Equipment. American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc., Atlanta 1996]

On the basis of PMV and PPD indexes, it is proposed to define limits of thermal comfort as satisfactory for 80% of people, which corresponds to the value of the PMV index contained within - 0.5 <PMV <+ 0.5 (Figure 1) [PN-EN ISO 7730:2006. Ergonomics of the thermal environment -- Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria; Parsons K. C.: Human thermal environments. Taylor & Francis, London and New York, 2003].

 

 

 

Fig. 1 Relationship between PMV and PPD [based on PN-EN ISO 7730: 2006] 

 

 

The PMV indicator is also used to classify thermal environments. In accordance with the Regulation of the Minister of Labour and Social Policy [Ordinance of the Minister of Labour and Social Policy of 16 June 2009 on the highest allowable concentrations and intensities of agents harmful to health in the work environment. DzU No. 105, item 873] the criterion for classifying the thermal environment to the area of ​​the hot microclimate is the PMV value ≥ +2, for the cold microclimate PMV ≤ -2 (Fig. 2)

 

 

 

Fig. 2 Criterion for classification of thermal environment

 

Tests are carried out at the workplace using microclimate meters.

 

 

HOT ENVIRONMENT

To determine the thermal load in a hot environment, the WBGT (Wet Bulb Globe Temperature) indicator is used [PN-EN ISO 7243: 2018-01 Ergonomics of the thermal environment - Assessment of thermal load using the WBGT indicator;Regulation of the Minister of Family, Labor and Social Policy of 12 June 2018 on the highest allowable concentrations and intensities of factors harmful to health in the work environment. Journal of Laws 2018 item 1286].

 

When determining the WBGT, measurements are required: wet bulb temperature of a naturally ventilated thermometer tnw, temperature of black globe thermometer tg, and in the case of tests outside the building also the air temperature ta. The method of conducting tests is described in the PN-EN ISO 7243: 2018-01 standard. The tests are carried out at the workplace using microclimate meters.

 

The calculated values of WBGT are then comparable with the admissible values recorded in the PN-EN ISO 7243: 2018-01 standard and the Regulation [Regulation of the Minister of Family, Labor and Social Policy of 12 June 2018 on the highest allowable concentrations and intensities of factors harmful to health in the work environment. Journal of Laws 2018 item 1286] (table 1).

 

Table 1. Admissible WBGT values, which can not be exceeded within the 8-hour daily working time [Regulation of the Minister of Family, Labor and Social Policy of 12 June 2018 on the highest allowable concentrations and intensities of factors harmful to health in the work environment. Journal of Laws 2018 item 12866]

 

 

COLD ENVIRONMENT

To determine the heat load (thermal debt) in a cold environment, the IREQ (Required Clothing Insulation) index and twc (wind chill temperature) indicator refer to the permissible local cooling of the organism [PN-EN ISO 11079:2008.Regonomics of the thermal environment – Deretmination and interpretetion of cold stress when using required clothing insulation (IREQ) and local cooling effects (oryg.)Regulation of the Minister of Family, Labor and Social Policy of 12 June 2018 on the highest allowable concentrations and intensities of factors harmful to health in the work environment. Journal of Laws 2018 item 1286].

 

IREQ is a measure of heat load caused by cold, integrating air temperature, average temperature of radiation, humidity and air velocity for specific levels of metabolic heat production. There is an indicator characterizing the clothing 's warmth, determined in the case of the general impact of the cold environment on the human body. The study of environmental parameters at the workplace is carried out using microclimate meters. Then IREQ values ​​are calculated based on the obtained results. For this purpose, you can use dedicated calculation programs. An example program for calculating the IREQ indicator can be found here: http://www.eat.lth.se/fileadmin/eat/Termisk_miljoe/IREQ2009ver4_2.html

 

An employee exposed to a cold environment is in a safe zone, when the heat-absorbing value of the clothing used falls within the IREQmin ÷ IREQneutral compartment (Figure 3). According to PN-EN ISO 11079, IREQmin is defined as the minimum value of required thermal insulation in order to maintain the thermal balance of the body at a constant level, assuming an average skin temperature of 30 ° C. IREQmin represents the highest acceptable level of psychophysiological stress (permissible general cooling of the body) during the work shift. In contrast, IREQneutral is defined as the thermal insulation of clothing required to maintain thermo-neutral conditions, i.e. the thermal balance of the body, in which the average body temperature is maintained at the correct level. Under these conditions the cooling is absent or minimal.

 

 

Fig. 3. Safe zone for an employee in a cold environment assessed using IREQ indicators

 

However, the limit values ​​for the twc index depending on the exposure time can be found in the Regulation of the Minister of Labour and Social Policy [Regulation of the Minister of Family, Labor and Social Policy of 12 June 2018 on the highest allowable concentrations and intensities of factors harmful to health in the work environment. Journal of Laws 2018 item 1286] (table 2).

 

Table 2. Limit values ​​of the twc index depending on the exposure time [Regulation of the Minister of Family, Labor and Social Policy of 12 June 2018 on the highest allowable concentrations and intensities of factors harmful to health in the work environment. Journal of Laws 2018 item 1286]

 

 

RISK ASSESSMENT

Three risk categories are accepted: high, medium, small [in Polish: Sołtyński, K., Marszałek, A., Obciążenia termiczny W: Ryzyko zawodowe Metodyczne podstawy oceny, pod red. M.W. Zawieska, Warszawa 2007, CIOP-PIB].

 

Occupational risk assessment in a hot environment is defined by means of the WBGT index (Figure 4) [in Polish: Sołtyński, K., Marszałek, A., Obciążenia termiczny W: Ryzyko zawodowe Metodyczne podstawy oceny, pod red. M.W. Zawieska, Warszawa 2007, CIOP-PIB].

 

 

Fig. 4. Risk assessment in a hot environment.

 

Occupational risk assessment in a cold environment can be defined using the IREQ and twc indexes (Figure 5).

 

 

Fig. 5. Risk assessment in a cold environment (IREQ).