Indoor Air Quality Health

Indoor air quality directly impacts human health through respiratory function, cognitive performance, and long-term disease risk. Poor IAQ contributes to acute symptoms and chronic conditions, with Americans spending approximately 90% of time indoors where pollutant concentrations often exceed outdoor levels by 2-5 times.

Health Effect Categories

Acute Health Effects

Immediate responses to poor indoor air quality:

Mucous Membrane Irritation

Eye irritation and burning sensation at VOC levels >500 μg/m³
Nasal passage inflammation from particulate matter >35 μg/m³ PM2.5
Throat irritation correlated with formaldehyde >0.1 ppm
Response typically occurs within minutes to hours of exposure

Central Nervous System Effects

Headaches from CO concentrations >35 ppm or CO₂ >1500 ppm
Dizziness and nausea at CO >100 ppm
Cognitive impairment measurable at CO₂ >1000 ppm
Fatigue and difficulty concentrating in poorly ventilated spaces

Respiratory Symptoms

Coughing and wheezing from particulate exposure
Shortness of breath in environments with inadequate ventilation
Asthma exacerbation from triggers including dust, mold, VOCs
Symptoms typically resolve after removing exposure source

Chronic Health Effects

Long-term consequences of sustained poor IAQ:

Respiratory Disease Development

Chronic obstructive pulmonary disease (COPD) from sustained particulate exposure
Asthma development in children exposed to high VOC concentrations
Reduced lung function from years of inadequate ventilation
Increased respiratory infection susceptibility

Cancer Risk

Lung cancer from radon exposure >4 pCi/L (WHO guideline 2.7 pCi/L)
Formaldehyde classified as human carcinogen at sustained >0.1 ppm
Asbestos fiber exposure causing mesothelioma risk
Benzene exposure linked to leukemia risk

Cardiovascular Effects

Particulate matter <2.5 μm penetrates deep into cardiovascular system
Increased risk of heart attack and stroke from chronic PM2.5 exposure
Blood pressure elevation in poorly ventilated environments
Systemic inflammation from long-term pollutant exposure

Major Indoor Contaminant Sources

Biological Contaminants

Microorganisms

Bacteria: Legionella pneumophila proliferating in water systems 20-45°C
Fungi: Aspergillus, Penicillium, Stachybotrys growing at >60% RH
Viruses: Airborne transmission enhanced in dry (<40% RH) conditions
Endotoxins released from gram-negative bacteria cell walls

Allergens

Dust mite proteins peak at 70-80% RH, 20-25°C
Cockroach allergens in droppings and body fragments
Pet dander particles 2.5-10 μm diameter
Pollen infiltration through inadequate filtration

Chemical Contaminants

Volatile Organic Compounds

Building materials: Formaldehyde from pressed wood (0.02-0.5 ppm typical)
Cleaning products: Limonene, 2-butoxyethanol, chlorine compounds
Furnishings: Flame retardants, plasticizers from vinyl and fabrics
Office equipment: Ozone from copiers, VOCs from printers

Combustion Products

Carbon monoxide from incomplete combustion (furnaces, water heaters)
Nitrogen dioxide from gas appliances (0.1-0.3 ppm typical indoor)
Particulate matter from cooking, smoking, fireplaces
Polycyclic aromatic hydrocarbons (PAHs) from incomplete combustion

Inorganic Compounds

Radon-222 from soil gas entering through foundation (half-life 3.8 days)
Asbestos fibers from deteriorating insulation or fireproofing
Lead particles from contaminated dust in older buildings
Mercury vapor from fluorescent lamp breakage

Particulate Matter

Size Classifications

PM10: Particles <10 μm, inhalable to upper respiratory tract
PM2.5: Fine particles <2.5 μm, penetrate deep into lungs
PM1.0: Ultrafine particles <1 μm, enter bloodstream
PM0.1: Nanoparticles <0.1 μm, potential cellular penetration

Sources

Outdoor infiltration through building envelope
Indoor generation from cooking, cleaning activities
HVAC system component wear generating particles
Occupant activities including movement resuspending settled dust

Ventilation Requirements for Health

ASHRAE Standard 62.1 Requirements

Outdoor Air Rates

Office spaces: 17 CFM/person + 0.06 CFM/ft² floor area
Classrooms: 10 CFM/person + 0.12 CFM/ft² floor area
Retail spaces: 7.5 CFM/person + 0.06 CFM/ft² floor area
Residential (62.2): 0.15 CFM/ft² + 3.5 CFM/bedroom + 7.5 CFM

Contaminant-Specific Ventilation

Smoking areas: 60 CFM/person (where permitted)
Laboratory spaces: 20 CFM/person minimum, exhaust-driven design
Industrial spaces: Contaminant generation rate determines requirements
Healthcare: 2-6 ACH outdoor air depending on space type

Ventilation Effectiveness

Air Distribution Performance

Mixing ventilation: Effectiveness factor 0.8-1.2
Displacement ventilation: Effectiveness factor 1.1-1.4
Under-floor air distribution: Effectiveness factor 1.2-1.5
Short-circuiting reduces effectiveness, requires computational fluid dynamics analysis

Ventilation Indices

Age of air: Mean time air molecule remains in space
Air change effectiveness: Ratio of nominal time constant to mean age
Local air quality index: Contaminant concentration at point relative to exhaust
Ventilation efficiency quantifies fresh air delivery

Filtration Requirements

Particle Filtration Standards

MERV Rating System (ASHRAE 52.2)

MERV	Particle Size Range	Efficiency	Application
6-8	3-10 μm	35-70%	Residential minimum
9-12	1-3 μm	50-90%	Commercial buildings
13-16	0.3-1 μm	90-95%	Healthcare, laboratories
17-20	<0.3 μm	>99.97%	Cleanrooms, isolation

Filter Selection Criteria

Initial resistance: 0.2-0.5 in. w.g. for MERV 8-13 filters at design airflow
Final resistance: 2× initial resistance typical replacement point
Holding capacity: Grams of dust retained before pressure drop excessive
System compatibility: Verify fan capacity handles increased static pressure

Gas-Phase Filtration

Activated Carbon Filters

Adsorption capacity: 10-30% by weight for typical VOCs
Contact time: 0.05-0.1 seconds minimum residence time
Breakthrough: Point where outlet concentration reaches 5% inlet
Regeneration: Thermal or steam desorption extends filter life

Potassium Permanganate

Oxidation mechanism: Chemically destroys formaldehyde, H₂S, mercaptans
No VOC desorption unlike physical carbon adsorption
Service life: 6-18 months depending on concentration and airflow
Indicator color change from purple to brown at exhaustion

UV Germicidal Irradiation

Design Parameters

Wavelength: 254 nm peak germicidal effectiveness
Dose: 5000-10,000 μW-sec/cm² for 90% inactivation typical pathogens
Installation: In-duct upper-room, coil treatment applications
Safety: Shield lamps to prevent occupant eye/skin exposure

Contaminant Monitoring

Carbon Dioxide Monitoring

Measurement Technology

Non-dispersive infrared (NDIR) sensors: ±50 ppm accuracy
Dual-wavelength compensates for lamp aging and contamination
Calibration: Annual verification against 1000 ppm reference gas
Sensor life: 10-15 years typical with proper maintenance

Interpretation

<800 ppm: Excellent ventilation, outdoor air-dominated
800-1000 ppm: Acceptable IAQ per ASHRAE guidelines
1000-1500 ppm: Marginal ventilation, cognitive performance decline
1500 ppm: Poor ventilation, immediate corrective action required

Particulate Matter Monitoring

Optical Particle Counters

Light scattering principle: Particle size and concentration
Size bins: Typical 0.3, 0.5, 1.0, 2.5, 5.0, 10 μm channels
Reporting: Mass concentration (μg/m³) or count (#/L)
Calibration: Monodisperse latex spheres traceable standards

Continuous Monitoring Thresholds

PM2.5 <12 μg/m³: EPA annual standard (24-hour: 35 μg/m³)
PM10 <50 μg/m³: WHO 24-hour guideline
Elevated levels trigger increased filtration or outdoor air intake
Trend analysis identifies sources and effectiveness of control measures

VOC Monitoring

Photoionization Detectors (PID)

Ionization potential: 10.6 eV lamp detects aromatics, ketones, aldehydes
Total VOC measurement: Calibrated to isobutylene equivalent
Detection range: 0.1-2000 ppm typical
Response time: <2 seconds for real-time monitoring

Gas Chromatography

Laboratory analysis for speciated VOC identification
Sampling: Sorbent tubes (Tenax, charcoal) or canisters
Detection limits: Low ppb to ppt range
Time-integrated samples represent average exposure

Biological Monitoring

Surface Sampling

Swab samples: Semi-quantitative viable organism collection
Tape lift: Microscopic examination of spore morphology
Culture analysis: Species identification, colony forming units
Interpretation: No universal threshold, compare to outdoor controls

Air Sampling

Spore trap: Impaction on adhesive surface, microscopic count
Impactor: Viable sampling onto growth media
Sampling volume: 75-300 liters typical
Results: Spores/m³ compared to outdoor and reference databases

Remediation Strategies

Source Control

Material Substitution

Low-VOC paints: <50 g/L VOC content per EPA standards
Formaldehyde-free pressed wood: CARB Phase 2 compliant
Green cleaning products: Third-party certified (Green Seal, EcoLogo)
Material emissions testing: Chamber testing per ASTM D5116

Moisture Control

Relative humidity maintained 40-60% to minimize mold growth
Water intrusion repair within 24-48 hours prevents colonization
Vapor barriers: Permeance <1 perm for crawlspace applications
Drainage: Grade away from foundation minimum 6 inches per 10 feet

Increased Ventilation

Dilution Ventilation

Temporary increase during high-emission activities
Post-occupancy flush-out: 14 days at design ventilation rate
Contaminant-based demand control: Real-time pollutant sensing
Calculation: Required ventilation = emission rate / (target - outdoor concentration)

Local Exhaust

Capture velocity: 50-100 FPM at contaminant source
Kitchen exhaust: 100-300 CFM per linear foot of cooking equipment
Laboratory fume hoods: 80-100 FPM face velocity
Bathroom exhaust: 50 CFM intermittent or 20 CFM continuous

Air Cleaning Enhancement

Portable Air Cleaners

Sizing: 4-6 air changes per hour for room volume
Clean air delivery rate (CADR): Effectiveness metric for particle removal
Filter replacement: Follow manufacturer schedule, typically 6-12 months
Placement: Away from walls, minimum 3 feet clearance for circulation

In-Duct Enhancement

Electronic air cleaners: 85-95% single-pass efficiency for particles >0.3 μm
Bipolar ionization: Ion generation claims require third-party verification
Media filters upgraded from MERV 8 to MERV 13 improves removal 40-60%
Pressure drop verification: Ensure fan capacity adequate after upgrade

Remediation Protocols

Mold Remediation

Containment: Negative pressure with HEPA exhaust, minimum -5 Pa differential
Removal: HEPA vacuum, damp wipe, disposal in sealed bags
Treatment: EPA-registered antimicrobials on non-porous surfaces
Verification: Post-remediation sampling <500 spores/m³ typical clearance

Asbestos Abatement

Licensed contractors required for friable asbestos removal
Wet methods: Minimize fiber release during removal
Air monitoring: Phase contrast microscopy <0.01 fibers/cc clearance
Encapsulation alternative for non-damaged materials

Sick Building Syndrome (SBS)

Characteristics

Non-specific symptoms: Headache, fatigue, eye/nose/throat irritation
No identifiable illness or cause
Symptoms improve when leaving building
Affects >20% of building occupants (WHO criterion)

Common Causes

Inadequate ventilation: <15 CFM/person outdoor air
Indoor pollutant sources: VOCs, particulates, biological contaminants
Poor humidity control: <30% or >60% RH
Psychological factors: Lack of control, noise, lighting