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Who issues what — the #1 trap
Enforceable vs. advisory
| OSHA (Dept. of Labor) | Enforceable PELs & regulations (29 CFR 1910). The only legally binding limits. |
| NIOSH (part of CDC) | RELs, IDLH values, research. Recommendations — not enforceable. |
| EPA | Guidance + regs on environmental media (radon, RRP, NAAQS). Mold = guidance only. |
| ACGIH | TLVs / BEIs. Health-based guidelines — explicitly not law. |
| ASHRAE | Consensus standards (62.1, 62.2, 55, 52.2, 188, 90.1). |
| ANSI/IICRC | S500 (water), S520 (mold), S540 (trauma) — consensus standards of care. |
| AIHA | Professional practice guidance (the mold "green book"). |
Mold has NO federal numeric standard. No OSHA PEL, no EPA action level, no "safe" spore count. Assessment compares indoor vs. outdoor + moisture + visual findings. If an answer states a numeric mold limit, it's wrong.
ASHRAE standards — memorize the numbers
| 62.1 | Ventilation — commercial/institutional |
| 62.2 | Ventilation — residential (dwelling units) |
| 55 | Thermal comfort |
| 52.2 | Filter test method → MERV |
| 188 | Legionellosis / water management |
| 90.1 | Energy efficiency |
ANSI/IICRC standards
| S500 | Water damage restoration |
| S520 | Mold remediation |
| S540 | Trauma & crime scene |
ACAC Code of Conduct core theme: avoid conflict of interest — keep assessment independent of remediation. Plus competence, honesty, confidentiality, objective reporting.
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Exposure limits & action levels
Gases & vapors
| CO — OSHA PEL (8-hr TWA) | 50 ppm |
| CO — NIOSH REL / ceiling | 35 / 200 ppm |
| CO — IDLH | 1,200 ppm |
| CO₂ — OSHA PEL | 5,000 ppm |
| CO₂ — ventilation guide | ~700 ppm > outdoor |
| Formaldehyde — PEL | 0.75 ppm |
| Formaldehyde — action / STEL | 0.5 / 2 ppm |
Particulates & metals
| Asbestos — OSHA PEL | 0.1 f/cc |
| Asbestos — excursion (30 min) | 1.0 f/cc |
| Lead — OSHA PEL | 50 µg/m³ |
| Lead — action level | 30 µg/m³ |
| Radon — EPA action level | 4 pCi/L |
| O₂ — deficient / enriched | <19.5 / >23.5% |
| O₂ — normal | 20.9% |
Don't confuse these
PEL ≠ REL ≠ TLV. CO is the classic trap: OSHA PEL 50 ppm (enforceable) vs. NIOSH REL 35 ppm vs. EPA outdoor NAAQS 9 ppm (8-hr). Formaldehyde PEL is 0.75 ppm — 0.5 is the action level, 2 is the STEL. CO₂ PEL is 5,000 ppm; ~1,000 ppm is only a legacy comfort rule-of-thumb, not a limit.
Occupational limits ≠ home limits. OSHA PELs and ACGIH TLVs are for healthy adult workers on an 8-hr shift — roughly 100–1000× less protective than health-based indoor guidance. Never apply a worker limit to a home or school. Health-based indoor refs: WHO formaldehyde 100 µg/m³ (30-min); EPA IRIS RfCs are chronic. Composite-wood emission limits (CARB/TSCA Title VI) are product-emission limits, not room-air.
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Water & EPA drinking-water MCLs
Key MCLs (40 CFR 141)
| Arsenic | 0.010 mg/L |
| Nitrate (as N) | 10 mg/L |
| Benzene | 0.005 mg/L |
| TTHM (annual avg) | 0.080 mg/L |
| HAA5 | 0.060 mg/L |
| Radium-226/228 (comb.) | 5 pCi/L |
| Gross alpha | 15 pCi/L |
| PFOA / PFOS (2024) | 4.0 ppt |
Lead & copper = action levels
| Lead — action level | 0.015 mg/L |
| Lead — LCRI (Nov 2027) | → 0.010 mg/L |
| Copper — action level | 1.3 mg/L |
| Basis | 90th %ile of tap samples (treatment technique, not an MCL) |
MCL vs MCLG vs action level. The MCL is the enforceable limit; the MCLG is the non-enforceable health goal (set to 0 for carcinogens like arsenic, benzene, lead). Lead & copper have no MCL — a treatment-technique action level at the 90th percentile instead.
Lead paint & asbestos (RRP / NESHAP)
| Lead-based paint = | ≥1.0 mg/cm² or ≥0.5% by weight |
| RRP applies | Pre-1978 housing / child-occupied; >6 ft² interior or >20 ft² exterior triggers it |
| Dust clearance (2024) | 5 / 40 / 100 µg/ft² — floors / sills / troughs |
| Soil-lead hazard | 400 ppm (play area) / 1,200 ppm (rest of yard) |
| Asbestos-containing material | >1% asbestos by PLM (exactly 1% is NOT ACM); point-count when ≤10% |
G
Assigned Protection Factors (OSHA 1910.134)
| Filtering facepiece (N95) & half-mask APR | 10 |
| Full-facepiece air-purifying respirator (APR) | 50 |
| Loose-fitting PAPR / supplied-air hood | 25 |
| Half-mask PAPR / SAR | 50 |
| Full-facepiece PAPR / SAR | 1,000 |
| Helmet/hood PAPR (with evidence) | 25 or 1,000 |
| Full-facepiece pressure-demand SCBA | 10,000 |
MUC = APF × PEL (maximum use concentration) — but the actual MUC can never exceed the IDLH or the cartridge/canister limit, whichever is lower. Ex: half-mask (APF 10) × 5 ppm PEL = 50 ppm calculated MUC.
A
Contaminants & health effects
Key facts
| Radon source / risk | Uranium decay in soil; #1 lung-cancer cause in nonsmokers |
| CO mechanism | Binds hemoglobin ~200–250× O₂ → carboxyhemoglobin |
| Formaldehyde | IARC Group 1; from urea-formaldehyde pressed wood |
| VOCs indoors | Often 2–5× outdoor; paints, adhesives, solvents |
| PM2.5 | Penetrates to alveoli; greatest particle risk |
| ETS | EPA Group A (known human) carcinogen, 1992 |
Legionella & combustion
| Legionella growth range | 77–113°F |
| Store hot water at | ≥140°F |
| Top aerosol source | Cooling towers → intakes |
| NO₂ source | Unvented gas/kerosene |
| Ozone generators | EPA: ineffective & unsafe |
| SBS vs BRI | BRI = identifiable cause; SBS = none, eases on leaving |
Radon protocol
| Action level | 4 pCi/L |
| Consider fixing | 2–4 pCi/L |
| Short-term test | 2–90 days |
| Long-term test | >90 days |
| Confirm with | Two short-term (avg) or one long-term; closed-building |
| Standards | ANSI/AARST consensus (measure & mitigate) — no federal MCL for radon in air |
B
Building science & moisture
Psychrometrics
| Relative humidity | Actual ÷ saturation vapor at that temp; temp-dependent |
| Dew point | Cool (const. moisture) to 100% RH → condensation |
| Grains per pound | 7,000 grains/lb; GPP = absolute moisture |
| Keep indoor RH | <60% (ideal 30–50%) |
| Dry wet materials in | 24–48 hr |
Air movement & water
| 3 driving forces | Stack effect, wind, mechanical (fan) |
| Stack effect (heating) | Infiltrate low, exfiltrate high |
| Wind pressure | + windward, − leeward/roof |
| Keep clean space | Positive pressure (contain = negative) |
| S500 Category | 1 clean · 2 gray · 3 black (contamination) |
| S500 Class | 1–4 = amount of water / evaporation load |
C
HVAC
Filtration & numbers
| HEPA | 99.97% @ 0.3µm |
| 0.3 µm = | most-penetrating size (worst case) |
| MERV scale | 1–16 |
| MERV for fine aerosols | ≥13 |
| Filters located | Upstream of coils |
Ventilation math
| Air changes / hr | ACH = (CFM×60) ÷ volume |
| 62.1 office rates | 5 cfm/person + 0.06 cfm/ft² |
| Dehumidify by | Cooling below dew point at coil |
| Economizer | Free cooling (more outdoor air) |
| ERV | Recover energy exhaust↔intake |
| DCV | CO₂-driven ventilation |
D
Equipment, sampling & calibration
Sampling
| Spore trap flow | 15 L/min |
| Andersen N6 impactor | 28.3 L/min = 1 CFM |
| Volume = | flow × time (15 × 10 = 150 L) |
| Culturable result | CFU/m³ (grows, speciates, slow) |
| Spore trap result | Counts live + dead, fast, limited ID |
| Outdoor reference | Indoor normally ≤ outdoor |
Calibration & QA/QC
| Primary standard | Soap-bubble / frictionless piston (Gilibrator) |
| Secondary standard | Rotameter (needs calibration) |
| Calibrate pump | Before & after, with media in-line |
| Field blank | QA/QC contamination check |
| Moisture meter | Compare to dry standard of same material |
ERMI & HERTSMI-2
| ERMI formula | Σlog₁₀(26 Group 1) − Σlog₁₀(10 Group 2) = 36 species |
| Method | MSQPCR — DNA, counts live + dead, on settled dust (accumulated) |
| Higher ERMI | More water-damage mold burden |
| EPA status | Research tool only — not validated for routine assessment |
| HERTSMI-2 | 5 species: A. penicillioides, A. versicolor, C. globosum, S. chartarum, W. sebi |
| HERTSMI-2 bands | ≤10 OK · 11–15 borderline · ≥16 problematic |
Bioaerosol method traps
| Positive-hole correction | Feller correction for multi-jet impactor counts at high loading |
| Culturable under-counts | Low CFU ≠ low mold — many spores non-viable; slow growers out-competed |
| Active vs background | Loose/settled spores = background; hyphae + conidiophores + spore chains = active growth |
F
Remediation
S520 Conditions
| Condition 1 | Normal fungal ecology (goal state) |
| Condition 2 | Settled spores / cross-contamination |
| Condition 3 | Actual mold growth (active or dormant) |
| Remediation goal | Return to Condition 1 |
Engineering controls
| Primary method | Moisture control + source removal |
| Limited containment | Single 6-mil poly |
| Full containment | Double poly + decon chamber, negative pressure |
| Air machine | Negative-air / HEPA AFD |
| Clearance (PRV) | Visibly clean, dry, no dust; independent |
EPA area-scaled tiers (Mold Remediation in Schools & Commercial Buildings, Table 2)
| Small <10 ft² | No containment · N95 + gloves + goggles · damp wipe / HEPA vacuum · in-house staff OK |
| Medium 10–100 ft² | Limited containment (professional judgment) |
| Large >100 ft² | Full containment · negative pressure + HEPA exhaust · full PPE |
Moisture control is the key to mold control. Dry wet materials in 24–48 hr; biocides/bleach are not recommended as a routine practice; the goal is to remove/clean contamination, not just kill it (dead mold is still allergenic); discard porous materials that can't be cleaned.
G
Respiratory protection
Filter classes (NIOSH 42 CFR 84)
| N series | Not oil-resistant |
| R series | Oil-Resistant (≤8 hr in oil) |
| P series | Oil-Proof |
| Efficiencies | 95 / 99 / 100 (=99.97%) |
| Magenta filter | = P100 |
Program (OSHA 1910.134)
| Medical evaluation | Before fit test / first use |
| Fit test — qualitative | Pass/fail (taste, odor, irritant) |
| Fit test — quantitative | Numeric fit factor |
| Fit test frequency | Before use, then annually |
| User seal check | Every time you don |
| IDLH / O₂ <19.5% | Requires SAR or SCBA |