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Effects Of Humidity In Volatile & Aromatic Compound Detection

Water vapour itself is the gaseous state of water and is invisible to the human eye

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A common frequently asked question is “can humidity interference affect my PID detector results?” Like many sensors and measurement instrumentation, traditional PIDs can indeed be affected by the environmental conditions i.e. dust, dirt and in particular, humidity. The major producers of oil & gas are located in the Gulf States and in or close to the Gulf of Mexico, which are of course areas of high temperature and high humidity.

Humidity Interference In VOC Measurements

Humidity is a natural phenomenon and is an amount of water vapour present in the atmosphere or in a gas. Water vapour itself is the gaseous state of water and is invisible to the human eye but we have all experienced how uncomfortable high humidity can make you feel.

Joel Sobel, a SVP with Accuweather offers a simple layman’s explanation. Think of the atmosphere as a sponge that can hold a fixed amount of water, let’s say a gallon (4 litres) of water. “If there is no water in the sponge, then the relative humidity would be zero”. Saturate the sponge with half a gallon of water; half of what it is capable of holding and that relative humidity climbs to 50 percent.

“The amount of moisture that the atmosphere can hold relates directly depends on the temperature”. Think of a rise in temperature like an increase in sponge size. A sponge that is half saturated with water is at 50 percent humidity. Now, increase the size of the sponge without adding more water. The relative humidity decreases because the bigger sponge is capable of taking on more moisture, but the same amount of water remains.
– PBS News Hour

Thinking about process industries such as the oil & gas sector, it is well knowing that during normal operations, leaks can occur from pumps, valves, flanges, storage tanks or during loading and unloading. According to US EPA figures , this can mean hundreds of tons of volatile organic compounds (VOC) including benzene, could potentially pose serious health risks

United States Environmental Protection Agency

What Is Humidity?

Humidity is a natural phenomenon and is an amount of water vapour present in the atmosphere or in a gas. Water vapour itself is the gaseous state of water and is invisible to the human eye but we have all experienced how uncomfortable high humidity can make you feel.

Humidity comes from water evaporating from lakes and oceans and since warmer water evaporates more quickly you find the most humid regions closer to warm bodies of water, like the Red Sea, the Persian Gulf and Miami, Florida.

Rather than absolute humidity, weather forecasters as well as engineers and scientists talk about relative humidity (RH) which is a ratio, expressed as a percentage, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity, is a function of both moisture content and temperature.

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“Humidity Interference In VOC Measurements”

The humidity interference in VOC measurements guide which can be downloaded below provides the reader with an in-depth balance of knowledge on a major limitation to the use of PIDs in the past was their susceptibility to ambient humidity, which is often found in hazardous environments. This is a particular issue in refineries which are typically located near water, or when measuring VOCs in steam, wastewater, or contaminated soil (which is usually moist). Recent PID designs provide almost no humidity effects, without the need for RH sensor compensation, desiccant tubes, or calibration gas humidification.

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