cal/cm? meaning

[bphgravity]

I have been try to come up with a good analogy or comparison to relate exactly what the cal/cm? incident-energy level means.

I understnad that a 1.2 cal/cm? (5 J/cm?) arc flash is sufficent exposure to receive a second-degree burn. But what is that equivalent to?

How do I explain what the difference is between an 8 cal/cm? and a 40 cal/cm? arc flash in terms that are easier to relate to. I am looking for something like comparing the energy received from an arc flash to that of standing in a giant microwave for a period of time. Is there a way to make this type of descriptive analogy?

Any ideas?

 

[ron]

Re: cal/cm? meaning

I have found that describing or showing pictures of the type of PPE needed for each of the 5 categories, and the associated range of incident energy ratings, get the point across.

 

[bphgravity]

Re: cal/cm? meaning

Is there a conversion formula to calculate the cal/cm? a 1000-watt microwave puts out in one minute?

There just doesn't seem to be an easy conversion formula to make cal/cm? a more understood quantity

 

[zog]

Re: cal/cm? meaning

Well a calorie is the amount of energy it takes to raise the temp of 1 gram of water 1 degree C, but I doubt that helps.

1.2 Cal/cm2 causes a 2nd degree burn in 0.1 seconds, if you had your oven on at 400 degrees F, opened the door, and put you hands on the hot metal part of the door, you would get a similar result, most people have burned themselves on an oven, so that helps to relate.

You can also look at some arc flash clothing test data that shows a typical cotton shirt bursting into flames at around 5 cal/cm2.

I have found that pictures are worth a thousand words, medical stock photos are available from most burn centers showing results of arc flash victims, that gets the point across.

 

[sfav8r]

Re: cal/cm? meaning

This photo and quote from Maintenance Technology might be helpful.

"A 10,000 A arc at 480 V is equivalent to 8 MW or approximately eight sticks of dynamite."...John Lane, electrical safety engineer at AVO Training Institute, Dallas, TX.

The photograph below shows a side view of an equipment rack during an arc flash explosion. (Photograph provided by Square D/Schneider Electric.)

Also, 1 calorie [I.T.] = 0.001163 watthour

[ April 04, 2005, 11:41 AM: Message edited by: sfav8r ]

 

[tepres]

Re: cal/cm? meaning

Saw this definition in "The Electrical Tester"
(a publication put out by Megger)


"... Unprotected workers exposed to an increase in skin temperature of 203 deg(F) for 0.1 second or 1.2 cal/cm^2 of energy may suffer second or third degree burns..."

If your skin is somewhere between room temp and 98.6 and you increase it by 203F as stated above, you'd probably be pretty close to that oven door zog spoke of earlier.

 

[kencybart]

Re: cal/cm? meaning

To bphgravity and company,
I just saw your original question today and thought you may still want to know that according to most sources, 1 cal/cm? is equivalent to holding the tip of your finger over a cigarette lighter for 1 second.
Your second question about the amount of energy a 1000 watt microwave gives off depends on how close you are to the microwave. Incident energy is expressed in calories per square centimeter of surface area. This value depends on how far away you are from the source. The closer you are, the greater the energy and vice versa.