Skip to main content

Test Methods and Cost Analysis

Understanding how ISO 8573 classes are verified and the cost implications of different air quality levels.

ISO 8573 Test Methods​

The ISO 8573 series includes specific standards for measuring each contaminant type.

ISO 8573-2: Oil Aerosol Testing​

Methods for measuring oil aerosol content:

MethodPrincipleDetection Range
GravimetricWeight gain on filter0.1 - 10 mg/m³
IR SpectroscopyInfrared absorption0.01 - 5 mg/m³
Photoionization (PID)UV ionization0.001 - 1 mg/m³
Gravimetric Method Setup:

    Compressed    ┌──────────┐    ┌──────────┐
    Air Supply ──→│ Pre-dry  │───→│ Sample   │───→ Exhaust
                  │ Section  │    │ Filter   │
                  └──────────┘    └────┬─────┘
                                       │
                                  Weigh before
                                  and after test

Procedure:

  1. Condition sample filter to constant weight
  2. Flow measured volume of compressed air through filter
  3. Re-weigh filter after test
  4. Calculate mg/m³ from weight gain and volume

ISO 8573-3: Humidity Measurement​

Pressure Dew Point measurement methods:

MethodPrincipleAccuracyResponse
Chilled mirrorSurface cooling until condensation±0.2°CSlow
Capacitive sensorPolymer absorbs moisture±2°CFast
Aluminum oxideImpedance change with moisture±2°CMedium
Electrolytic (P2O5)Current from water electrolysis±1°CSlow
Chilled Mirror Hygrometer:

         Light source
              │
              ▼
         ┌─────────┐
    Air──│ Mirror  │──→ Exhaust
         │ Surface │
         └────┬────┘
              │
         Temperature
         sensor + cooler
              │
              ▼
         Dew point reading
         when condensation detected
Pressure vs Atmospheric Dew Point

Always specify Pressure Dew Point (PDP) at operating pressure. A -40°F PDP at 100 PSIG equals approximately -60°F atmospheric dew point.

ISO 8573-4: Particle Counting​

Particle measurement methods:

MethodPrincipleSize Range
Light scattering (OPC)Laser diffraction0.1 - 25 μm
Light blockingShadow detection1 - 100 μm
MicroscopyVisual counting0.5 - 100 μm
Cascade impactorInertial separation0.1 - 10 μm
Optical Particle Counter (OPC):

         Laser beam
              │
              ▼
         ═════════════
    Air ────────────────→ Exhaust
         ═════════════
              │
              ▼
         Photodetector
         counts scattered light pulses

Isokinetic Sampling: Sample velocity must match pipe velocity to avoid particle bias.

Vsample=VpipeV_{sample} = V_{pipe}

ISO 8573-5: Oil Vapor Testing​

Methods for oil vapor (not aerosol):

MethodPrincipleSensitivity
Activated charcoal tubeAdsorption + solvent extraction0.001 mg/m³
Direct-reading PIDPhotoionization0.01 mg/m³
GC-MSGas chromatography mass spec0.0001 mg/m³

Charcoal Tube Method:

  1. Draw measured air volume through charcoal tube
  2. Desorb with carbon disulfide
  3. Analyze by gas chromatography
  4. Calculate concentration

ISO 8573-6: Gaseous Contaminants​

Tests for:

  • Carbon monoxide (CO)
  • Carbon dioxide (CO2)
  • Sulfur dioxide (SO2)
  • Nitrogen oxides (NOx)
  • Hydrocarbons

Method: Detector tubes or continuous gas analyzers

ISO 8573-7: Viable Microorganisms​

Colony Forming Units (CFU) per m³:

MethodDescription
ImpactionAir impacts on agar plate
FiltrationMembrane filter + incubation
ImpingementBubbling through liquid media

Testing Frequency​

ApplicationParticleHumidityOilMicrobial
General industrialAnnualQuarterlyAnnual-
Food/beverageQuarterlyMonthlyQuarterlyQuarterly
PharmaceuticalMonthlyWeeklyMonthlyWeekly
ElectronicsMonthlyContinuousMonthly-
Medical/breathingContinuousContinuousContinuousDaily

Cost-Benefit Analysis​

Capital Cost by Air Quality Class​

ISO ClassEquipment RequiredRelative Capital Cost
4.6.4Basic filtration + refrigerated dryer1x (baseline)
2.4.2High-efficiency filtration + refrigerated dryer1.5x
1.4.1Multi-stage filtration + refrigerated dryer2x
1.2.1Multi-stage + desiccant dryer3-4x
1.1.1Full treatment + activated carbon + monitoring5-8x

Operating Cost Comparison​

Example: 500 CFM system, 8,000 hours/year, $0.10/kWh

ISO ClassPressure DropDryer TypeAnnual Energy Cost
4.6.45 PSIRefrigerated$3,200
2.4.28 PSIRefrigerated$4,100
1.2.112 PSIDesiccant (heatless)$8,500*
1.1.115 PSIDesiccant + carbon$10,200*

*Includes purge air losses

Hidden Costs of Over-Specification​

Common Mistake

Specifying Class 1.1.1 "just to be safe" when 2.4.2 would suffice can cost 3-4x more with no benefit.

Example waste calculation:

Unnecessary desiccant dryer vs. refrigerated:

  • Extra capital: $15,000
  • Extra annual energy: $4,000
  • 10-year cost: $55,000 wasted

Hidden Costs of Under-Specification​

ProblemCost Impact
Equipment failureDowntime + repairs
Product contaminationScrap, recalls, liability
Corrosion damagePiping replacement
Process issuesQuality problems

Example: Food plant contamination event

  • Production stop: 3 days
  • Product disposal: $50,000
  • Investigation: $10,000
  • Equipment sanitization: $15,000
  • Customer notification: $5,000
  • Total: $80,000+ (plus reputation damage)

ROI Analysis Framework​

Calculate True Cost of Compressed Air​

Cost per 1000 SCF=Annual energy costAnnual SCF÷1000\text{Cost per 1000 SCF} = \frac{\text{Annual energy cost}}{\text{Annual SCF} \div 1000}

Typical costs: 0.15−0.15 - 0.30 per 1000 SCF

Treatment Equipment ROI​

Formula:

Payback (years)=Capital costAnnual savings or avoided losses\text{Payback (years)} = \frac{\text{Capital cost}}{\text{Annual savings or avoided losses}}

Example: Upgrading filtration to prevent paint defects

  • Filter upgrade cost: $2,500
  • Current defect rate: 2%
  • Production value: $500,000/year
  • Defect cost: $10,000/year
  • After upgrade defect rate: 0.2%
  • New defect cost: $1,000/year
  • Annual savings: $9,000
  • Payback: 3.3 months

Selecting the Right Air Quality​

Decision Matrix​

If your application has...Consider...
No product contactClass 4-5 (basic)
Indirect product contactClass 2-3
Direct product contactClass 1-2
Sensitive instrumentationClass 1-2
Breathing airClass 1 + continuous monitoring

Industry-Specific Guidelines​

IndustryTypical SpecificationRationale
Automotive painting1.4.1Oil-free for paint adhesion
General manufacturing4.6.4Basic protection sufficient
Food packaging1.2.1 to 2.4.1No moisture, minimal oil
Pharmaceuticals1.2.1Strict contamination control
Semiconductor1.1.1Ultra-clean required
Textile4.6.4Humidity control primary concern
Best Practice

Start by identifying the most sensitive application in your facility. That determines minimum quality. Use point-of-use treatment to upgrade only where needed.

Measurement Equipment Costs​

EquipmentTypical CostMeasurement
Handheld dew point meter500−500 - 2,000Humidity spot checks
Inline dew point transmitter1,000−1,000 - 3,000Continuous humidity
Particle counter (portable)5,000−5,000 - 15,000Particle spot checks
Oil vapor detector2,000−2,000 - 8,000Oil spot checks
Full ISO 8573 test kit20,000−20,000 - 50,000Complete analysis
Third-party lab testing500−500 - 2,000/testPeriodic verification