InspectAPedia ^®

• What causes False Negative or "OK" Toxic Mold Test Results - and why are these a Source of Error in Indoor Mold Tests
• What are the sources of variation in the mold level that air tests can detect?

Here we define and explain the causes of False Negative or "OK" Toxic Mold Test Results as Sources of Error in Indoor Mold Tests. This document is a brief tutorial which provides information about the accuracy of and sources of errors in tests for the level of allergenic and toxic mold in residential buildings: Are spore counts valid? Are cultures and swab tests valid? These critical questions are discussed in this paper. Readers should also see MOLD LEVEL IN AIR, VALIDITY, and for a more in-depth critique of popular mold testing methods than this tutorial see MOLD TESTING METHOD VALIDITY

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

High Risk of False Negative Results in Mold Tests

Mold spore counts are questionable in the first place, given the high variability that we discuss in this article. But "low" or "negative" mold spore counts, especially if not accompanied by a thorough visual inspection and collection of the building's leak history and occupant complaint history, are particularly suspect.

Individual samples of particles in air show tremendous variation from minute to minute, making "ok" airborne mold spore test results a thing to view with skepticism.

Examples of factors which can cause an exponential difference in particle levels in indoor residential air over short time intervals include: mechanical disturbance (walking across a carpet or moving a moldy cardboard box), operation of hot air heating system or central air conditioning system, operation of other building fans, particularly ceiling fans and vacuum cleaners, turning lights on and off, and opening or closing windows and doors. In situations of particular risk, additional or periodic testing should be considered.

Below we list these sources of mold test variation and give photos and mold test examples for specific variation sources.

Our experience is that the variation in the level of small (mold spore sized) indoor airborne particles is so significant that any indoor airborne particle count is likely to be an inaccurate guess at the actual occupant exposure level where indoor problematic molds are present. This means that visual inspection, building history, and occupant complaints or occupant health fragility need far more attention than they receive if the "mold investigator" simply performs a cursory visual inspection or worse yet, simply collects a few air samples in a building.

At Conditions that Cause High Variation in Indoor Airborne Particle Levels this article list some of the chief sources in the short term variation in the level of airborne particle levels. Even if we used a long term sampling method, say 24 hours, or interval sampling over days, these same variations will occur, and worse, without careful study of the actual sources of airborne particle level variation in a specific building, and without a documentation of the typical conditions in the building during the time that it is occupied we cannot describe the occupant exposure level with any accuracy whatsoever.

Risk of false negative mold tests: Experienced mold contamination investigators should have little confidence that a one-time low or "ok" "toxic mold test spore count" is an assurance that problematic particles are not present.

The presence of certain spores or fungal particles, even at low levels in air can indicate or confirm an indoor reservoir and amplifier of mold spores in the building, particularly if a careful microscopic examination of the "low level" sample contents shows evidence of nearby active fungal growth such as Aspergillus sp. or Penicillium sp (or certain other genera/species) spore chains. The presence of extensive off-season pollen can also indicate a pollen reservoir in the building - a potential concern for people with pollen allergies or asthma.

Share this Article      

...

Technical Reviewers & References

Search InspectAPedia

• Daniel Friedman - principal author/editor of the InspectAPedia^® Website
• InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
• Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
• Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

ENVIRONMENTAL HAZARDS GUIDE
AIR POLLUTANTS, COMMON INDOOR
ALLERGEN TESTS for BUILDINGS
ALLERGY TESTS for PEOPLE
ALLERGY TEST ACCURACY
FLOODS IN BUILDINGS-priorities
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
MOLD: A COMPLETE GUIDE TO MOLD
MOLD INFORMATION CENTER
ACCURACY OF VARIOUS MOLD TEST METHODS
  Causes of Variation in Airborne Particle Levels
  Indoor vs. Outdoor Spore Counts
  Extent of Variation of Airborne Particle Counts
  Particle Levels vs Sampler Height
  Particle Levels vs Windows/Doors
  Particle Levels in Ducts
  Concentration Bursts of Mold Spores
  False Negative Results in Mold Tests
  Mold Culture Plate Test Errors
  Why Use Airborne Mold/Particle Sampling?
  Visual Inspection and History for Mold
ACTION GUIDE - WHAT TO DO ABOUT INDOOR MOLD
ALLERGEN TESTS for BUILDINGS
ALLERGY TESTS for PEOPLE
ALLERGY TEST ACCURACY
CLEARANCE INSPECTIONS - MOLD CLEANUP
DO IT YOURSELF MOLD CLEANUP
ENERGY SAVINGS in BUILDINGS
ENERGY SAVINGS PRIORITIES
ENERGY SAVINGS RETROFIT CASE STUDY
ENERGY SAVINGS RETROFIT LEAK SEALING GUIDE
ENERGY SAVINGS RETROFIT OPTIONS
FIND MOLD in BUILDINGS, HOW TO
HIDDEN MOLD
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INDOOR AIR QUALITY IMPROVEMENT GUIDE
INDOOR AIR QUALITY METHODS COMPARED
LEAD POISONING HAZARDS GUIDE
MOISTURE CONTROL in BUILDINGS
MOLD ACTION GUIDE - WHAT TO DO ABOUT MOLD
MOLD AGE - Old is the Mold?
MOLD APPEARANCE - WHAT MOLD LOOKS LIKE
MOLD APPEARANCE - STUFF THAT IS NOT MOLD
MOLD ATLAS & PARTICLES INDEX
MOLD BY MICROSCOPE
MOLD CLASSES, HAZARD LEVELS
MOLD CLEANUP GUIDE- HOW TO GET RID OF MOLD
MOLD REMEDIATION CLEARANCE INSPECTION
MOLD DETECTION & INSPECTION GUIDE
MOLD DOCTOR?
MOLD EXPERT, WHEN TO HIRE
MOLD EXPOSURE RISK LEVELS
MOLD EXPOSURE STANDARDS
MOLD INSPECTORS & MOLD TESTERS
MOLD LEVEL IN AIR, VALIDITY
MOLD LEVEL REPORTS
MOLD LEVELS IN BUILDINGS
MOLD by MICROSCOPE
MOLD ODORS, MUSTY SMELLS
MOLD PREVENTION GUIDE
MOLD RELATED ILLNESS GUIDE
MOLD RELATED ILLNESS SYMPTOMS
MOLD SPRAYS, SEALANTS, PAINTS
MOLD STANDARDS
MOLD TEST KITS
MOLD TEST KITS for DIY MOLD TESTS
MOLD TEST PROCEDURES
MOLD TEST REASONS
MOLD TESTING METHOD VALIDITY
ODORS, Smells, Gases in Buildings-Diagnosis & Cure
RENTERS & TENANTS GUIDE TO MOLD
SEWAGE BACKUP TEST & CLEANUP
STAIN DIAGNOSIS
TECHNICAL & LAB PROCEDURES
THERMAL TRACKINGld

• Thanks to Susan Flappan, Flappan Consulting, moldetect.com, Overland Park KS, 913-402-1131, for contributing comments and some suggested text from ACGIH Bioaerosols: Assessment and Remediation 12/2006.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Books, Complete List of Environmental Inspection, Diagnosis, Cleanup, Air Quality & Design, Inspection, Repair Books at the InspectAPedia Bookstore
• Environmental Health & Investigation Bibliography - our own technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
• ...

More Information on Building Diagnostic Inspections and Repairs

• Mold Information Website Home Page
• Mold Classes: what types of cosmetic, allergenic, or toxic mold are a problem? Can mold be cleaned-up successfully?
• Toxic Mold, Allergenic Mold: How Much is Bad?
• Validity of Bulk Surface or Tape Sampling
• Validity of mold cultures and "home test kits"
• Validity of culture methods for toxic mold inspections
• What to look for in a toxic survey report or toxic mold test lab report
• Plant Flower Tree Pollen - a Photo ID Library for asthma and allergy sufferers

InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

Building Inspection, Problem Diagnosis, Forensic Investigation & Testing, Repair Consulting

Contact Daniel Friedman for website content suggestions or for fee-paid consulting