Environmental Lab. Don Pugh. Ergonomics

Transcription

1 Envronmental Lab Don Pugh Ergonomcs

2 1. Introducton The purpose of ths lab s to measure aspects of the envronment, specfcally nose, heat, humdty, and lghtng and to relate these factors to human productvty n the work place. ~hen any of these factors exceed the recommended standards human stress occurs and productvty s lowered. 2. Nose 2.1 Audometrc Survey Hearng may be accurately measured on an audometry ~ s set up so that the lstener cannot see settngs or The meter nterpret from the tester's body language that a sgnal s beng sent. The range of decbels s tested n gradually ncreasng ntervals from low to hgh ( to 7 db) for a range of frequences from low ptched sound at 25 to hgh ptched frequences hertz. of 8, Results are shown n Graph 1. Fg. 1 : Audometrc Survey of Hearng Insert Graph 1 Here The graph ndcates some mnor hearng loss n both ears at the lower frequences. Hearng mproves n the hgher frequences, although less so n the rght ear at 6 hertz. The greatest senstvty s at 4 hertz. In general, the hearng s excellent and would cause no mpedments n the work place. A hearng

3 mparment s defned as an average hearng threshold shft n excess of 15 db at 5, 1 and 2 hertz(mccormck & Sanders, 1987). The above results contrast wth the norm. The human ear s less senstve at low frequences and more senstve at hgher frequences. ~>~Hearng loss normally occurs around 4 db and spreads to a range from 3 to 6. Results may have been confounded by ntal room nose and unfamlarty wth the tones. Sound Levels A sound pressure meter was used to take readngs around the campus. Usng ANSI standards the meter measures on the A, B and C scales. The A scale s used to measure envronmental nose and approxmates the response characterstcs n human hearng. C scale weghs all frequences equally and does not conform The wth human hearng. The long term average sound level or Leq (equvalent sound) level, a measure used for the sze of envronmental nose was also measured over a 3 mnute perod. TTS or temporary threshold shft s used to measure hearng loss caused by contnuous sound levels. Results are presented n Fg. 2. Fg. 2 : Sound Level Readngs on Murdoch Campus Insert Fg. 2 Here Interpretaton of the results ndcates that all levels of nose are below the mnmal standards of 9 db shown to cause hearng loss over long perods. The Leq sustaned average was 55 and

4 ths level falls wthn the range of clercal envronments. The cafetera was the nosest envronment and the lbrary the quet est. The lbrary compares wth the 42 db' level n a quet home(mccormck & Sanders, 1987). 2. Heat For the body to operate comfortably, a body core temperature of 37 C must be mantaned.heat exchange occurs va convecton, evaporaton (sweatng), radaton or conducton. Heat exchange s nfluenced by ar temperature, humdty, ar flow and temperatures of the surroundng envronment.wth hgh ar and contact surfaces coolng occurs by evaporaton. Ths process s lmted by the amount of mosture n the ar or humdty. Humdty s calculated by comparng readngs of a wet and dry bulb thermometer. The wet bulb, wet wth water, s cooled by evaporaton caused by ar movement from swngng the nstrument for one and a half mnutes. The readng s below the temperature of the dry bulb. The relatve humdty ratng s calculated by subtractng the wet from the dry readng and consultng a table. The black body thermometer s a wet thermometer enclosed n a large copper black bulb whch s heated by radaton. An ndex of radatoe heat s provded. Ths ndex s called the WBGT ndex. The ndex combnes the effects of dry heat wth humdty and radaton. The WBGT formula s (.7,~wet temperature)*(.2,black bulb)*(.1?~dry temperature).

5 The ET or effectve temperature s an ndex to equate temperature, humdty and ar currents. A effectve temperature of 21 C s charactersed by a sensaton of 21C wth 1 percent humdty. Heat stress ndces or HSI s the rato of heat load caused by metabolsm, convecton and radaton to the evaporatve coolng potental of the surroundngs. Ths ndex measures the ablty of the body to shed heat. The physologcal effects of heat stress s hgher rectal temperature, ncreased heart rate and dehydraton. Performance decreases wth people undertakng lght work better toleratng hgher WBGT. Heaver work requres more frequent rest breaks. A table of permssble workloads for contnuous work durng the day at gven temperatures ndcates 75$ rest per hour at 3 WBGT and 5 Rcal/Hr(Cormack and Saunders, 1987). These wrters note that mental and cogntve tasks are mpared the least, followed by trackng and dual tasks. Exposure s also traded off aganst the degree of ET. Longer exposure lowers the degree of ET requred to affect performance. Readngs around campus are shown n Table 2. Table 2 Cafetera Lbrary Bush C urt Wet Bulb C Dry Bulb C Black Bulb C Ref Humdty WBGT Index ETA Scale C These results ndcate values n the comfort range n the lbrary

6 and mld humd weather outdoors. The cafetera because of ts lack of ar condtonng falls between the two poles. All condtons are acceptable and would not cause stress or lmt work. 3. Lghtng Whte lght ncludes all wavelengths of the spectrum, and s defned as radant energy capable of exctng the retna of the eye. The domnant wave length determnes colour. Lumnance s the value assocated wth reflected lght and gves us our awareness of brghtness. Lumnous flux s the measurement quantty measured n lumen (lm). Lumnous ntensty s measured n candela (cd). Saturaton or purty refers to the presence of a narrow range of wavelengths, gvng colour or chroma. Any colour can be created by mxng the three prmary colours, red, green and blue. Effects of Lghtng on Performance Although performance levels off wth ncreased levels of llumnaton, hgher levels of llumnaton may ncrease mental capacty by ncreasng vsual acuty. Excessve llumnaton may cause glare and eye stran. Sanders and McCormack provde standards suggestng 5 to 1 lux for medum contrast vsual tasks such as readng medum pencl hand wrtng. In comparson the followng classroom measures were found. Measurements n the classroom appear n Table 3. Table 3 : Lght Readngs n the Classroom Lght readng of lumnous ntensty (Brghtness)

7 68 to 72 at 1 meter. Average 7 candela Reflected Lght from Desk (Illumnaton) 368 to 384 lux Measurement of Illumnaton of a work place 243 to 275 lux Ths lghtng level s recommended as sutable for hgh contrast vsual work such as readng prnted materal(sanders & McCormck, 1987, 48). The level s satsfactory for a classroom. It would be nadequate for ntensve draftng requrements. Increased lghtng levels may be requred for elderly people. The reflected lumnance from the desks may be excessve, causng reflected dscomfort glare. Glare refers to greater brghtness than the lumnance to whch the eye s adjusted. 4. Concluson Comfort n terms of heatng, lghtng, and nose levels are essental for optmal functonng of human bengs. Ths laboratory has demonstrated that condtons wthn the unversty generally meet the standards for comfort presented by Saunders and McCormck (1987).

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9 db Levels 1 Nose Levels on Campus Corrdor Cafetera Bush Court Lbrary Locaton ~ db A db C MEASUREMENT SCALES