Infrared Thermography
By Ken VanBree
This month's issue is devoted to indoor air quality. You may wonder what today's modern imaging technology has to do with air quality. Read on and I will introduce you to the wonders of infrared thermography.
As you know, cameras record images using visible light. Early photographers took pictures using black and white film that recorded differences in the intensity of light. The resulting black and white prints were often "colorized" to make them more familiar to the human eye that can distinguish an entire spectrum of colors. Colors at the upper (shorter wavelength) end of the spectrum appear blue or violet to our eye. Colors at the lower (longer wavelength) end of the spectrum appear red.
Visible light is only a small portion of the electromagnetic spectrum. Above the visible spectrum are ultraviolet rays, the ones that give you a sunburn, and X-rays that are used for medical diagnosis. Below the visible spectrum are infrared rays, micro waves and radio waves that carry radio and TV signals. Infrared rays are given off by warm bodies. They radiate heat. You have probably experienced them if you sat at an outdoor restaurant that used heat lamps to keep their customers warm.
Although the human eye can't "see" infrared wavelengths, there are sensors called bolometers that can measure the strength of the infrared waves much the way that digital cameras record the strength of the visible light. The resulting infrared images give information about an object's temperature much the way a photograph shows us an object's color.
The above images show two views of the same wall taken at the same time. The image on the left is a photo taken with a conventional digital camera. It shows a portion of a wall where the baseboard has been removed. Other than the missing baseboard and carpet the wall looks perfectly normal.
The image on the right has a thermal image superimposed over part of the wall. The thermal image has been colorized with cool areas in blue, and warmer areas in warmer colors. In this image, you can see that the lower portion of the wall is significantly cooler than the upper portion of the wall. This is because there was a flood in the room on the other side of the wall that resulted in significant water damage. The lower foot of the wall is still wet from the flooding and evaporation of the water, which cools the wall. It could remain wet for days or weeks if it is not actively dried.
There are several forms of mold that feed on the paper that forms the outer skin of wall board. If this wall stays wet for more than 48 hours, there is a good chance that mold will grow inside the wall. Periodic wetting and drying caused by an intermittent water leak could grow a lot of mold inside a wall with- out ever being visible outside the wall. Mold spores can become airborne and adversely effect indoor air quality.
Thermal images can improve air quality be- cause they are useful in detecting water leaks that aren't visible to the naked eye. Early leak detection can help stop mold growth before it becomes a problem.
May 2006 Builder Architect Edition Issue