IOSR Journal of Applied Physics (IOSR-JAP) e-ISSN: 2278-4861.Volume 7, Issue 1 Ver. I (Jan.-Feb. 2015), PP 60-66 www.iosrjournals.org DOI: 10.9790/4861-07116066 www.iosrjournals.org 60 | Page An Estimate of Thermal Comfort in North-Central Region of Nigeria A.A. Musari 1 , O.A. Sojobi 2 , O.A Abatan 3 A.I. Egunjobi 4 1, 3, 4 Physics/Electronics Unit, Department of Science Laboratory Technology, Moshood Abiola Polytechnic, Abeokuta, Nigeria 2 Department of Mathematics and Statistics, Moshood Abiola Polytechnic, Abeokuta, Nigeria Abstract: Heat Index describes the combined effects of temperature and humidity on human body. The Heat index expresses an apparent temperature felt by human body that cools slower at higher values of the relative humidity due to the reduction in the rate of evaporation .This study aimed at describing the comfort and discomfort periods caused by heat stress in some selected urban towns in five states of the North central region in Nigeria. Monthly data of Temperature, Relative Humidity and Wind speed for thirty years (1980-2009) obtained from Nigerian Meteorological Agency were used to calculate the Temperature-Humidity indices(THI) and Wind-chill index(WCI) for the five urban towns in North central region investigated. The results showed that severe heat stress were experienced in the months of April, May and March in descending order for Abuja, Minna, Lokoja and Bida while moderate heat stress were recorded in June, October, July, September and August for all these four towns where 50% of human and animals are not comfortable due to hot and humid weather condition. Remarkable, pleasant and comfortable sensations were observed throughout the year in Jos with exception of November, December and January which shows that 50% of inhabitants are partially comfortable due to cold and humid weather. The percentage frequency charts for all the five towns investigated were also presented in this study. Keywords: Temperature-Humidity Index, Wind-Chill Index, Heat stress, Percentage Frequency I. Introduction Nigeria is found in the tropics, where the climate is seasonally damp and very humid. The country experiences consistently high temperatures all year round. Since temperature varies only slightly, rainfall distribution over space and time becomes the single most important factor in differentiating the seasons and climatic regions. Nigeria has two major seasons, the dry and wet season, the lengths of which vary from north to south. The extent to which the thermal environment challenges the body’s thermoregulatory mechanisms is referred to as the environment heat or thermal stress. The concept of the heat stress index as well as heat exposure assessment plays a fundamental role in integrating knowledge of human responses to the heat in a way which can be used to specify safe working conditions (Pourmahabadian et al 2008). Atmospheric conditions which include relative humidity, temperature, wind, solar radiation, air pollution and precipitation greatly affect living creatures including human beings. There is always a certain limit beyond which these conditions are no longer tolerable by them (human beings, animals and plants). Whenever this limit is exceeded, disaster and stress is inevitable. Hospitals record increased admission during days with high temperature (Ballester et al., 1997; Basu and Samet 2002; Pauli and Rizzi, 2005). The physiological sensation of human and animal comfort is influenced by heat stress. In hot regions and seasons discomfort level is raised by heat stress as well as increase in mortality rate among the aged and those who constantly suffer from malnutrition (Jauregul, 1984; Oke, 1982; Okpara, 1997). The effect of heat stress is mostly felt in the urban areas. Temperature, relative humidity and wind speed being some of the meteorological parameters determine heat stress. Some of the comfort indices which can be computed from these meteorological parameters include Temperature-Humidity Index (THI), Discomfort Index (DI), Wind Chill Index (WCI) e.t.c. A temperature-humidity index (THI) is a single value representing the combined effects of air temperature and humidity associated with the level of thermal stress. This index has been developed as a weather safety index to monitor and reduce heat stress related losses. Different animal species and human have different sensitivities to ambient temperature and the amount of moisture in the air. Venkitshwaran and Seaminathan (1967) used Thom’s Index to calculate human comfort for some selected stations in India during different hours. Prasad and Pawar (1982) investigated the diurnal variations of Thom’s Index for different months of the year for Bombay. Hossain et al (1983) also used Thom’s Index to calculate the human comfort for almost all the stations in Bangladesh for different months at 0600BST and 1800BST. They also utilized Siple and Passel (1945)’s Wind Chill Index to evaluate daily comfort during winter for Dhaka. Okpara (2002) evaluated the physiological sensation of human comfort or discomfort for Akure