Classify Category vs Class First On Arrival Decision Tree

Why this matters

The first two decisions on a water loss are category (how contaminated the water is) and class (how much evaporative load there is). They drive entirely different parts of the response: category sets PPE, cleaning vs removal, and worker/occupant safety; class sets equipment quantity and drying-system design. Sequencing matters because category gates whether you can dry a material in place at all, while class only matters once you know what you are allowed to keep. Classify category first: a Category 3 loss can make a low-class drying plan irrelevant because porous materials must come out regardless of how fast they would have dried. Reversing the order leads to crews setting air movers in contaminated water and to scope that the standard will not support.

Symptom presentation

The tech arrives to standing or absorbed water and must read two independent dimensions:

• Category indicators: clarity, odor, source, tide-line color, residue, and time/temperature exposure. Clean supply water vs gray appliance discharge vs black sewage/floodwater.
• Class indicators: how much wet surface area exists, how much water the materials hold, and whether low-evaporation (wet but bound) materials dominate. A few wet square feet of carpet is a different class than a saturated room with wet structural cavities.

Quick checks

Category, in order:

1. Identify the source. Broken supply line or rain through a clean roof points Cat 1; dishwasher, washing machine, or sink-drain overflow points Cat 2; sewage, ground/surface floodwater, or any wastewater points Cat 3.
2. Read clarity, odor, and residue. Clear/odorless vs cloudy/soapy vs turbid/foul with biosolids.
3. Apply the clock. Cat 1 that sits and contacts contaminants, or sits long in warm conditions, deteriorates toward Cat 2 then Cat 3. Time and temperature reclassify.

Class, after category:

1. Estimate wet surface area and material porosity. Minimal wet area in part of a room with low-porosity materials trends Class 1; an entire room with carpet/pad and wicked walls trends Class 2; ceilings, walls, insulation, and large wet areas trend Class 3; materials with low permeance/evaporation (hardwood, plaster, concrete, multilayer assemblies) define Class 4 specialty drying.

Isolation tree

• Source is clean and water is clear/odorless, freshly occurred. Branch: Category 1. Proceed to classify class; most materials are candidates for in-place drying.
• Source is gray (appliance, sink drain) or Cat 1 water that has aged or contacted soils. Branch: Category 2. Clean or remove based on porosity; carpet pad typically removed, structural materials cleaned and dried.
• Source is sewage, floodwater, or grossly contaminated, or Cat 2 aged past the point of control. Branch: Category 3. Porous materials are removed; non-porous cleaned and disinfected. Class becomes secondary because removal, not drying, governs porous materials.
• Category settled, now read class: minimal wet area, low-porosity materials. Branch: Class 1, light equipment load.
• Whole-room wet, carpet/pad, walls wicked up a foot or two. Branch: Class 2, moderate load.
• Ceilings/walls/insulation wet over a large area. Branch: Class 3, heavy load, top-down airflow.
• Low-evaporation/bound-moisture materials dominate (hardwood, plaster, masonry, multilayer). Branch: Class 4, specialty drying with low-GPP/desiccant strategy and longer timelines.

Confirming diagnosis

• Per S500, category is a measure of contamination at the time of assessment and can change with time and temperature; document the basis (source, indicators, exposure) and re-evaluate if conditions worsen.
• Class is determined by the rate of evaporation expected from the materials and the amount of wet material, which sizes the dehumidification and airflow. Confirm class by quantifying wet surface area and identifying low-permeance materials.
• The two are orthogonal: a Category 3 loss can be any class, and a Class 4 loss can be Category 1. Record both independently in the file with the evidence for each.
• Reassess category at every visit; a Cat 2 left without proper control will trend toward Cat 3 (see the clock-vs-condition standard guidance).

Remediation

• Set PPE and worksite controls to the category before any drying equipment is placed. Cat 2 and Cat 3 require escalating respiratory, skin, and containment controls.
• For Cat 3, remove porous materials per the standard before designing the drying system; do not run air movers across contaminated water (it aerosolizes contaminants).
• Size dehumidification and airflow to the class once category-driven removals are scoped. Class 4 materials get a low-humidity/desiccant or specialty approach, not just more air movers.
• Document category and class on the scope; both numbers justify the equipment, removals, PPE, and timeline to the adjuster.

References

• ANSI/IICRC S500-2021, Standard for Professional Water Damage Restoration, Section 10 (Categories of Water) and Section 11 (Classes of Water Intrusion), including time/temperature reclassification guidance.
• ANSI/IICRC S520-2015, Standard for Professional Mold Remediation (microbial amplification risk in Cat 2/3 and delayed losses).
• OSHA 29 CFR 1910.1030, Bloodborne Pathogens (PPE and exposure controls applicable to Category 3 sewage work).
• EPA, A Brief Guide to Mold, Moisture, and Your Home (EPA 402-K-02-003), moisture-control basis for category escalation over time.