Classes of Water Loss - When to Change?

December 9, 2003
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Should removing the carpet and pad change the class?


I recently heard from an IICRC-certified technician who asked, "When processing a Class 2, Category-1 water loss, if I remove the carpet and pad, does that loss change from a Class 2 to a Class 1 water loss?"

Good question.

As the IICRC technical advisor, I respond to questions about classes of water loss along the guidelines being taught in IICRC-approved water restoration technician (WRT) and applied structural drying (ASD) courses. It is important to understand the verbiage used in defining classes of water loss as written by the IICRC ASD Technical Advisory Committee (TAC). With the categories of water (1-3, or "clean; gray; black.") in mind, the classes of water loss defined by the IICRC ASD TAC are:

Class 1: Slow Rate of Evaporation
Water losses affecting only part of a room or area; or losses with low-permeance/porosity materials (e.g. plywood, particle board, structural wood, VCT, concrete). Little or no wet carpet and/or cushion is present (or damage is confined to a small area, or wet for a short period). Minimum moisture is absorbed by materials, which release that moisture slowly.

Class 2: Fast Rate of Evaporation
Water losses affecting an entire room of carpet and cushion. Water has wicked less than 24 inches up walls. There is moisture remaining in structural materials (e.g. plywood, particle board, structural wood, VCT, concrete).

Class 3: Fastest Rate of Evaporation
Water may have come from overhead. Ceilings, walls, insulation, carpet, cushion and subfloor in virtually the entire area are saturated.

Class 4: Specialty Drying Situations
These losses involve wet materials with very low permeance/porosity (e.g. hardwoods, subfloor, plaster, brick, concrete, stone, crawlspaces). Typically, there are deep pockets of saturation that normally require very low specific humidity.

The reason the technician asked his question is that his method for arriving at initial dehumidifier capacity on a loss was based on the class of loss. An insurance company representative questioned the amount of equipment used on that loss, and certainly there is nothing wrong with that; I wish that more insurance companies would question procedure and pricing methodology to learn more about drying science and why trained, certified technicians make the decisions they do. In this instance, the insurance company representative said that when the carpet and pad was removed, it changed the class of loss.

Starting Dehumidification Initially, effective drying of wet materials requires that air in a structure be processed based on the dehumidifier's Association of Home Appliance Manufacturers (AHAM) rated ability to remove a specific number of pints per day. On-going equipment use is based on psychrometric calculations to verify adequate and safe drying progress.

For example, a 1,500-square-foot Class 2 water loss with 8-foot ceilings equals 12,000 cubic feet. Dehumidifier capacity is based on testing by AHAM at 80 degrees and 60-percent relative humidity. Our industry has experienced a significant leap in dehumidifier technology during the last few years. Not only are dehumidifiers larger, but pint for pint, they far more efficient in the way in which they process air to achieve dehumidification.

Once I know the cubic feet of air within a wet structure and I know the class of water loss, I then must understand the type of dehumidifier I have available. I won't get into an extensive discussion of the differences in "conventional" and "low-grain" refrigerant and desiccant dehumidifiers here; suffice it to say that conventional refrigerants are able to produce or "output" dry air efficiently with specific humidity in the range of 52 to 60 grains per pound (gpp) of dry air, while low-grain refrigerants are able to output dry air efficiently in the range of 30 to 35 gpp. Certainly, desiccant dehumidifiers are able to output dry air efficiently in the 5 to 10 gpp range; however, there is a price to pay in terms of energy consumption and the practical matter of available electricity. Of course, along with reduced specific humidity, there is a corresponding reduction in vapor pressure, which is the mechanism for drawing moisture out of wet structural materials and contents.

These three factors (cubic feet of air; class of loss; dehumidifier type) are used to determine "initial" dehumidifier capacity requirements on a given job. Continuing the example, with 12,000 cubic feet of air in a Class 2 loss with LGR dehumidification equipment available, I can use the IICRC "starting dehumidification" chart (Chart 1) to select a number to divide into the total cubic feet of air in the wet structure. This allows me to arrive at the total number of pints to remove in the first 24 hours to begin drying this structure (and contents) efficiently. In this case:

240 pints - 12,000 ft3 ÷ 50 (LGR dehumidifier) = 240 pint/24 hour requirement at AHAM (80°F/60% RH)

If the LGR dehumidifier I have available has an AHAM-tested removal rating of 120 pints in 24 hours, I can determine that the number of dehumidifiers needed to begin drying this job efficiently is two (240 pints/24 hours ÷ 120 AHAM-rated pints = 2).

When carpet and pad is removed from a structure, if the claim is automatically changed from a Class 2 loss to a Class 1 loss, this means that the LGR dehumidifier requirement is cut in half, i.e. a divisor of 100 for Class 1 vs. a divisor of 50 for Class 2, even though we are dealing with "moisture remaining in structural materials." Worse still, using conventional refrigerant dehumidifiers, the initial dehumidification requirement would be cut by a full 60 percent.

This is the basis for my disagreeing with changing the class of loss based on removal of saturated carpet and pad. My reasons are several:

1. Foremost is the very definition of Class 1 and Class 2 losses. There is a huge difference between a Class 1 loss that is confined to only part of a room, caught quickly, and therefore, minimum moisture has been absorbed by materials, and a Class 2 loss that has significant absorption of water in structural materials (and contents).

2. This point was never discussed at more than eight ASD two-day Task Force meetings that I attended as recording secretary. In particular, this issue is not addressed in the IICRC ASD exam. Therefore, I can only assume that it is a foregone conclusion that, other than minor adjustments based on qualified technician judgment, the starting Class of loss would remain the same throughout the drying project, with the technician making adjustments based on psychrometric readings as drying progresses.

3. Carpet and pad are by far the easiest materials to dry. Today, on properly extracted and properly equipment-specified Class-2 water losses, we have no problem drying carpet and pad in 24 to 36 hours. Indeed, laboratory testing by the International Society of Cleaning Technicians (ISCT) proves that up to 97 percent of water can be extracted from carpet and pad with state-of-the-art technology. Often the carpet is dry in 8 to 12 hours. It is the structural materials that are difficult and time consuming to dry.

4. Microbial growth on carpet or pad, both of which are 100 percent synthetic, and on both of which air movement and evaporative cooling are maximized, is all but impossible (ref. "Mold and Carpet Research," Berry, et al, Carpet and Rug Institute, 2001). However, cellulose-based structural materials (e.g., plywood, OSB, studs, joists, underlayment) are perfect food sources if not dried quickly and effectively with confirmation provided by documented moisture content recordings. There simply is too much at risk to cut back to save a few dollars.

5. While a company or technician setting and monitoring the job may decide to reduce the initial number of air movers on a Class 2 loss with carpet and pad removed, I maintain that the starting dehumidification requirement should remain the same. Obviously, the ASD TAC-specified starting dehumidification may change based on psychrometric readings collected during daily monitoring trips to check individual jobs.

One highly respected colleague, who is also an IICRC-approved WRT/ASD instructor, pointed out that if highly absorbent materials like carpet and pad are removed from a wet structure, the rate of evaporation is far less and, therefore, the need for dehumidification equipment is much less. He went on to say that he could not, "...without further information on the actual loss, degree of saturation or full description of building materials, give a conclusive classification. However, I can easily determine that less dehumidification would be necessary than that [required] of a Class 2 [loss] for the reasons stated above."

While I agree that the amount of evaporated water would be less without carpet and pad, and that more information regarding the specific loss would be useful, considering the "typical loss" that IICRC-certified firms handle day-in and day-out, I still would start with the table's initial dehumidifier capacity recommendations. Why?

  • Unfinished wood has a lot of surface water, and there may even be some pooled water in areas that are difficult to extract physically. Thus, on a "typical loss," there still may be quite a bit of water to capture for the first eight to 12 or even 24 hours.
  • I would want to get the vapor pressure as low as possible as quickly as possible to continue the migration of moisture from wood and from difficult-to-access areas: behind molding, under counters or built-in fixtures, under sill plates, and in other pockets of saturation. Frankly, I look forward to the day when I can trim a day or two off our average drying time, due to advanced training and technology, just as we have done in the last five years.
  • If inconvenienced homeowners decide to turn off any equipment, it will be noisy drafty air movers rather than dehumidifiers. The dehumidifier may wind up being the only unit left to do the job.
  • I probably would adjust the amount of equipment on the first monitoring trip (either increase or, more likely, decrease), based on psychrometric readings, not only to save money for my customer, but also for a positive marketing impact with the insurance company.
  • Any odor is amplified by heat and humidity. As a side benefit, the dryer the air, and the faster the drying, the fewer the complaints we hear about normal household odors from three sources: building materials, household soils, and, 72 percent of the time, animal urine or dander.

    I am not particularly worried about microbial growth and odor on carpet; it is the structural materials that concern me. Bottom line, I'm going to err on the side of caution for that first 24 hours.

    It is with these points in mind that my professional opinion, shared by IICRC leadership, is to maintain the starting dehumidification capacity using the initial Class of water loss, regardless of the presence of carpet and pad for the first 24 hours. After that, adjustment in equipment (either adding or subtracting) will be based on psychrometric data, materials present and industry standard-of-care judgment exercised by qualified and competent restoration contractors.

    I anticipate that, at a minimum, this issue will be revisited during the re-writing of IICRC S500 in 2004, at which time the language can be simplified, clarified and/or expanded to avoid confusion as much as possible.

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