The heat is on, and it looks to be another cracker of a summer. Heat domes have been working the continent from one end to the other, setting new records, and offering up punishing conditions to anyone working outside. At times it’s dangerously hot.
We’re all familiar with the long-used term “heat index” which is derived from the effects of the relative humidity applied to the actual air temperature, yielding what is sometimes also called the apparent or “feels-like” temperature. The relationship is simple: As actual air temperature, relative humidity, or both, increase the heat index increases, along with the physiological stressors on the human body, while physical comfort decreases. This can have profound effects on job performance and safety.
It’s very important to understand that actual and apparent temperatures, forecasted and observed, are measured and calculated only in and for shaded locations. Exposure to direct sunlight may require an upward adjustment of up to 15°F to the standard heat index to compensate.
All temperature measurements of record are necessarily in-the-shade temperatures. This eliminates variability that would otherwise skew all of the data. To accomplish this, a white louvered box called a Stevenson Screen is the semi-standardized instrument shelter used at almost all weather stations, and there are siting and exposure standards for these shelters as well. Among other things, the National Weather Service requires that thermometers be mounted 5 feet (+/- 1 foot) above the ground, and that the ground over which the shelters are located should be “typical of the surrounding area.” That typically means grass or dirt, not asphalt or concrete, and for data-gathering purposes it makes sense. Unfortunately, it does not accurately reflect the conditions as we feel them while working in the sun on steel decks.
For 104 years and counting, the official site for measuring and collecting weather data for New York City is on a small hill next to Belvedere Castle in Central Park. It’s a lovely location. But it bears no resemblance to standing in the sun on the deck of a tank barge spinning valves while loading cargo at IMTT — Bayonne, N.J., on a smoking hot July afternoon.
