How do I calculate the Wind Chill Temperature Index in the Work Environment section of the Cold Work tab, in OHS Online?
That's a really important question! Let's look at how this works more closely then. The calculation of the Wind Chill Temperature Index takes into account the main factors which affect the ability of a person to work in low temperature conditions. To calculate this index, let's break the process into a number of parts:
Part 1: Determining the environmental temperature in which the cold work will be done The first part of determining the Wind Chill Index Number (WCIN), is to record the temperatures at which the work takes place and enter these into the Work Environment section. The temperature should be easily recordable, since the environment in which the work will be done should have its temperature monitored. In the Work Environment section, there are two fields which require the work temperature to be recorded:
In some cases, both of these temperatures might be the same. If they are, enter the temperature details and then use the general working temperature for calculating the WCIN. If the two temperatures differ, then use the minimum temperature for calculating the WCIN (worst case scenario). For this example, let's say the minimum temperature and the general temperature are the same and the temperature is monitored at minus 25 degrees Centigrade (-25 deg.C).
Part 2: Determining the wind chill (air flow) of the environment in which the cold work will be done The second part of determining the Wind Chill Index Number (WCIN), is to record the air flow speed of the environment at which the work takes place and enter this into the Work Environment section. Air flow is recorded using an instrument called an anemometer.
If an anemometer is not available, then the Work Environment section provides a very rough means to determine an approximate air flow in the work environment. This is described in the Work Environment section of the Cold Work tab. Let's use the example given in the Work Environment section description. We gauge the air flow roughly and determine that our flag moves slightly in the airflow, indicating an approximate airflow of up to 8km/h. This gives us our rough air flow, which we record by checking the Up to 8km/h option.
Part 3: Determining the Wind Chill Index Number The third part of determining the Wind Chill Index Number (WCIN), is to use the Wind Chill Temperature Index chart to determine the actual WCIN. Before this is done, record whether the moisture in the air is low, moderate or high. This may not be very easy to determine but can be helpful if you have a good idea. Basically, the greater the moisture in the air, the lower the time period a person can operate in the low temperature environment. The WCIN is now determined by taking the two values we have determined (temperature of -25 deg.C and air flow value of 8km/h) and referencing them on the index chart; when using our values, we see we get a WCIN reading of -33:
When determining the WCIN, we did the following:
1. WCIN - Temperature - the temperature was easy to determine on the chart because its value matches that of one of the values on the chart.
2. WCIN - Airflow - the value of the airflow does not exactly match a value on the chart. Rather its value lies between the 5 and 10 wind speed values. Therefore, we take the 10 value (worst case scenario) as our windspeed value.
3. WCIN - Determination - our index value of -33 falls into the light blue colouring with black text. This corresponds to the 10 - 30 minutes period in the Frostbite Guide at the bottom of the chart. From this we now know that persons working in the cold environment must not be in the environment for longer than 30 minutes at most.
Part 4: Enter the Wind Chill Index Number details into the PTW The fourth part of determining the Wind Chill Index Number (WCIN), is to enter the relevant details into the PTW so they are recorded. The WCIN details are entered into the Work Environment section of the Cold Work tab in the following fields:
1/. The Wind Chill Temperature Index Number field:
2/. The relative exposure risk field in the Frostbite Guide (our example indicates a 10 - 30 minutes maximum exposure):
The WCIN details are also entered into the Precautionary Safety Measures section of the Cold Work tab, since the WCIN determines the maximum period of time a person can safely operate in the low temperature conditions. The following fields are completed:
1/. The Work and Rest Period fields (time is recorded in mins):