Talk:Wet-bulb globe temperature
|WikiProject Occupational Safety and Health||(Rated Start-class, Low-importance)|
The formula is not from the page. The formula belongs to the ACGIH. I have re-written it, but I think It can be no-standard (no the same that the created by the standard body, this is, the ACGIH.
Fix or delete
If anybody is watching this, this article needs a major fixup or deletion.
In particular, I'd like to know:
- Where this was ever used.
- When it was used.
- Any other measurements used for a similar purpose.
- What units were used in this unit-dependent formula? Note in particular that as a general rule, multiplying temperatures only makes sense if you are using an absolute scale, either kelvins or degrees Rankine. But I suspect that this formula was used with either degrees Celsius or degrees Fahrenheit, and it won't be comparable at all in the other scale.
Gene Nygaard 13:09, 30 Jan 2005 (UTC)
Reply to Gene The temperatures are summed, not multiplied. So, the end result is in the same units as the originals. This is actually a really novel way to measure temperature, because it gives you the "wind chill" and the "heat index" all in one, at any temperature and humidity. However, when solar radiation is "negiligible" , we eliminate the dry-bulb temperature, rather than the black bulb temperature. Now, they really should read the same thing if there's no solar radiation, but I'm going to fix it. Phonon266737 (talk) 23:40, 31 July 2009 (UTC)
Reply to Q4 This formula really is independent of units since the factors all add up to 1.
General There is no definition for wet bulb temperature as a measure of humidity given, and I'm not sure that it is identical with saturation temperature. I think we need this as it is widely used. --188.8.131.52 roger thorpe
I changed the formula below: Indoors, or when solar radiation is negligible, the following formula is used: WBGT = 0.7Tw + 0.3Td because, as it states, it is for indoor, or when solar radiation is negligible, as the formula, as it was written had 0.3Tg for using the black globe thermometer. Since there is no solar radiation, there would be no logical reason to use the black globe termometer, as it is used to measure the heat increase as a product of wind and solar radiation. — Preceding unsigned comment added by 184.108.40.206 (talk) 18:42, 21 August 2011 (UTC)
It was previously correct. I'd suggest not changing cited formulas on a whim, because of a hunch or impartial knowledge. I will fix the article up in a bit, as there is several fundamental errors in it which make it confusing. Specificlaly, the notion that a globe thermometer is only affected by the sun. BarrenAvalanche (talk) 21:11, 23 August 2011 (UTC)
WBGT Indoors uses a Globe Thermometer
I noticed it has been changed several times in the logs. The use of a globe thermometer is correct for WBGTi. As seen in the publications from ISO and ACGIH. The globe thermometer measures radiant heat, and while the sun obviously produces it - so to does other objects.BarrenAvalanche (talk) 21:15, 23 August 2011 (UTC)
This is just sort of an explanation of everything, when I get a couple of minutes I'll try and write a draft of WBGT that can actually be used as the article. In particular, I'd suggest some time is spent on the history of WBGT (which i'm not familiar with). As well as put a chart - i'd suggest the most current published ACGIH TLV chart and the one currently there. (I'm not sure wiki protocol on using/citing published sources, as I imagine there is a certain format / regulations)
Then obviously the formulas. Apparently they need to be explained - judging by the amount of times it is incorrectly editted and the focus solely on solar radiation. I'll cover that.
In order for the human body to function properly (Enzymes and all that good stuff to work), the body must be regulated at ‘normal’ temperature. Hyperthermia or Heat Stress occurs if the body’s internal temperature rises above this normal temperature (~>38C). Thermoregulation of the body occurs through evaporative cooling. Evaporative cooling is where the body secretes sweat, which then rests on the skin. In order for this liquid to evaporate, energy is needed. This energy is taken from the surrounding area by lowering the temperature which cools it – hence evaporative cooling.
Some factors affect the body’s ability to perform this. Exercise or extensive physical activity, heats up the body internally which makes it more prone to heat stress. Fortunately, after exposed to similar work regimens for several consecutive days (4-5 work days) the body begins to acclimatize and work more efficiently.
Externally, the body can be affected by the conventional big three of heat transfer: convection, conduction and radiation. These heat the body. Clothing can also affect this as it can hold the liquid to one’s skin and limit moisture evaporation which obviously impairs the cooling.
Since the rate of moisture evaporation is so important with heat stress, I measure several parameters which affect this ability. While there are different standards to do so, (Humidex and Heat Index are sort of simplified versions), OSHA, CCOHS (the ones I’m familiar with) as well as many other different countries use WBGT. This is also an international standard; I’ll have to double check the number though (ISO ____).
WBGT uses a combination of wet bulb, dry bulb and globe temperature to calculate (as well as coefficients for clothing worn and varying threshold limit values for activity levels / acclimatization). From this, ACGIH publishes TLV which outline how much rest is needed per hour. This allows for us to consider other factors such as humidity (water more readily evaporates in drier conditions, once saturated evaporation becomes difficult), wind (if there is wind it’ll better distribute the evaporated water instead of concentrating it in area while it diffuses), and radiation (every single object emits / absorbs heat energy through thermal radiation, colder object obviously emit less and absorb more. Solar radiation is a portion but not the only means of).
Two different methods are used to calculate this based on the presence of radiant heat sources, known as WBGT outdoors. This can be slightly confusing as the sun is a radiant heat source, but being outdoors and in the shade eliminates this (the two objects are obstructed so there isn’t a radiative transfer between them) so WBGT indoors is used. Likewise, while indoors a radiant heat source such as a furnace or hot machinery, WBGTo is to be used. This is done to better model how the body feels the heat, as skin’s emissivity is very high so it does absorb a lot (WBGTo uses a dry bulb to sort of lower the WBGT reading as a globe temperature is the highest value and raises it so much more on the comparative scale – hence making the TLVs have to be higher).
Dry Bulb: The temperature typically used. It is a thermometer that is shielded to just measure the air temperature and disregard other factors such as radiant heat.
Wet Bulb: A thermometer covered in a wick. This thermometer is cooled by evaporative cooling, and therefore takes into affect parameters such as wind and humidity. This accounts for convection and evaporation. It is the ‘coldest’ of the three temperatures.
Globe: This is a thermometer surrounded by a black copper ball. This ball is to mimic the emissivity of skin and absorbs all of the radiant heat from nearby sources (which heats the air inside the ball and thus thermometer). Again radiant heat is emitted from everything, some objects more readily than others. Hotter temperature objects generally emit more radiant heat. — Preceding unsigned comment added by BarrenAvalanche (talk • contribs) 02:15, 6 September 2011 (UTC)
Is the current name of this article (Wet Bulb Globe Temperature) properly capitalized? Some sources capitalize the term this way, but several use all lowercase (hse.gov.uk, ccohs.ca, sciencedirect.com). In addition, I found the following spelling variations:
- WetBulb Globe Temperature (CamelCase)
- Wet-bulb globe temperature (hyphen)