Flashcards in 10.1 d Temp. and Thermal Environment Deck (11):
Corrected Effective Temperature Index (CETI)
As the ETI did not take into account the effects of radiant heat, it was later modified to form the Corrected Effective Temperature Index (CETI). The basis for this index was to use a 150mm diameter black globe thermometer measurement (radiant heat) on the scale, in place of the dry bulb reading (air temperature).
The predicted 4-hour sweat rate (P4SR) index
measures sweat rate as a function of climate stress, and uses a nomogram to predict the quantity of sweat given off by fit, acclimatised young men exposed to the environment for four hours.
Wet bulb globe temperature (WBGT) values are calculated from one of the following equations:
With direct exposure to sunlight (outdoors) WBGT out = 0.7 NWB + 0.2 GT + 0.1 DB Without direct exposure to the sun (indoors) WBGT in = 0.7 NWB + 0.3 GT
The heat stress index (HSI) is
a comparison of evaporation required to maintain heat balance (Ereq), with the maximum evaporation that could be achieved in that environment (Emax). HSI = Ereq \ Emax x 100
Engineering controls can be an effective way of reducing heat stress and preventing or minimising occurrence of heat illness. Examples include: 9
Increasing air movement using fans. Installing shade structures to reduce radiant heat from the sun. Installing shields or barriers to reduce radiant heat from sources such as furnaces or hot vessels. Removing heated air or steam from hot processes using local exhaust ventilation. Insulating indoor workplaces. Installing air conditioners or coolers to reduce air temperature. Locating hot processes away from people. Insulating /enclosing hot processes or plant. Using mechanical aids to reduce physical exertion.
Management controls Heat stress can be reduced by attention to the way work is organised, for example: 6
Rescheduling work so the hot tasks are performed during the cooler part of the day, or in cooler times of the year. Reducing the time an individual spends doing the hot tasks, for example: by job or task rotation. Arranging for more workers to do the job. Making sure there is easy access to cool drinking water. Providing additional rest breaks in cool, shaded areas. Providing training and information to enable workers to: - identify hazards - recognise symptoms of heat stress and heat illness - understand how to avoid heat illness.
Suitable clothing and PPE may help to further reduce the risk of heat illness, for example: 4
broad brimmed hat appropriate protective clothing to cover workers at least between elbow and knee, however long sleeves and trousers provide the best protection sunscreen sunglasses.
As wind chill is the most critical factor in the onset of cold stress, engineering controls that reduce exposure to the wind are useful. The two common approaches are:
Wind barriers (shields) which can be effective outdoors or against circulated air indoors in freezer rooms. Refuges, which are warm areas equipped with warm drinks, so that workers can retreat to rest. The ideal is for the required task to be performed inside the refuge.
Other engineering controls for cold stress include: 6
Avoiding metal tools and thermally insulating metal handles and bars. Provision of local heating. Mechanical aids to reduce manual handling requirements (and the potential for perspiration). Designing machines and tools to be operated without having to remove mittens or gloves. Designing workplaces so that operators are not required to sit or stand for long periods in cold conditions. Reducing air velocity in cool rooms / chillers while workers are required to work inside.
Management controls for cold stress 10
Monitoring of air temperature, air velocity and equivalent chill temperature. Work-rest schedules with adequate rest breaks to warm up between periods of moderate to heavy work activity. Information and training about the symptoms of adverse health effects from exposure to cold and suitable precautions. Medical screening of workers. Workers who are suffering from respiratory or cardiac diseases or taking medication which interferes with normal body temperature regulation should be excluded from work in cold environments. Acclimatisation periods. An acclimatisation period of around one week is recommended for new workers. Extra attention should be paid to those returning to work after an extended absence from cold exposure situations due to illness. Supervision to monitor for signs and symptoms of workers exposed to potentially hazardous cold conditions. Self-reporting of illness, medication, alcohol intake and other factors that may influence susceptibility to cold stress. Self-paced working at temperatures below -12°C. Work rates should not be so high as to cause heavy sweating that will result in wet clothing. Encourage healthy life-styles. A good diet and physical conditioning help protect against abnormal cold. Nicotine and alcohol should be avoided. Administrative controls for arranging work in such a way that sitting still or standing still for long periods is minimised. Where possible work should be scheduled for the least cold part of the and long shifts, and excessive overtime should be avoided in the cold.