Safety Classifications

ASHRAE Standard 34 Classification System

ASHRAE Standard 34 establishes a two-character alphanumeric safety classification system for refrigerants based on toxicity and flammability characteristics. This classification system provides a standardized framework for evaluating refrigerant safety and determining appropriate application requirements.

Safety Group Designation Format

The safety group consists of two characters:

• First character (letter): Indicates toxicity class (A or B)
• Second character (number): Indicates flammability class (1, 2L, 2, or 3)

Example: R-410A is classified as A1 (lower toxicity, no flame propagation)

Toxicity Classifications

Class A Refrigerants (Lower Toxicity)

Class A refrigerants have an Occupational Exposure Limit (OEL) ≥ 400 ppm based on time-weighted average (TWA) exposure over an 8-hour workday.

Characteristics:

• Lower acute and chronic toxicity
• Minimal health effects at typical exposure concentrations
• Wider application range permitted by codes
• Reduced ventilation and detection requirements compared to Class B

Common Class A Refrigerants:

*R-717 is Class B despite the OEL value shown for comparison **Ammonia is classified as Class B2L due to toxicity considerations beyond OEL

Class B Refrigerants (Higher Toxicity)

Class B refrigerants have an Occupational Exposure Limit (OEL) < 400 ppm or exhibit evidence of toxicity at concentrations below 400 ppm.

Characteristics:

• Higher acute or chronic toxicity potential
• Stricter application limitations
• Enhanced ventilation requirements mandatory
• Refrigerant detection systems required
• Restricted use in occupied spaces
• Equipment room design requirements more stringent

Common Class B Refrigerants:

*Values vary based on jurisdiction and application

Exposure Limit Metrics

Time-Weighted Average (TWA): $$TWA = \frac{\sum(C_i \times T_i)}{8 \text{ hours}}$$

Where:

• C_i = Concentration during exposure period i (ppm)
• T_i = Duration of exposure period i (hours)

Short-Term Exposure Limit (STEL):

• 15-minute TWA exposure limit
• Should not be exceeded at any time during workday
• Typically 3× to 5× the 8-hour TWA OEL

Immediately Dangerous to Life or Health (IDLH):

• Maximum concentration from which escape is possible within 30 minutes without irreversible health effects
• Critical for emergency response planning

Flammability Classifications

Class 1: No Flame Propagation

Criteria:

• No flame propagation when tested per ASTM E681
• Lower Flammability Limit (LFL) not determined
• Heat of combustion < 19,000 kJ/kg

Examples:

• R-134a (HFC-134a)
• R-404A (HFC blend)
• R-507A (HFC blend)
• R-744 (CO₂)

Application characteristics:

• Unrestricted by flammability concerns
• Standard electrical equipment permitted
• No special ignition source controls required
• Suitable for all occupancy types

Class 2L: Lower Flammability

Criteria:

• Lower Flammability Limit (LFL) > 0.10 kg/m³
• Burning velocity ≤ 10 cm/s
• Heat of combustion < 19,000 kJ/kg
• Limited flame propagation

Examples:

• R-32 (difluoromethane) - LFL: 0.307 kg/m³
• R-1234yf (HFO-1234yf) - LFL: 0.289 kg/m³
• R-1234ze(E) - LFL: 0.303 kg/m³
• R-717 (ammonia) - LFL: 0.116 kg/m³
• R-454B (blend) - LFL: 0.252 kg/m³

Burning Velocity Comparison:

Application requirements:

• Charge limits based on room volume
• Refrigerant detection may be required for larger charges
• Standard electrical equipment generally acceptable
• Mechanical ventilation recommended for equipment rooms

Class 2: Flammable

Criteria:

• Lower Flammability Limit (LFL) ≤ 0.10 kg/m³
• Burning velocity ≤ 10 cm/s
• Heat of combustion ≥ 19,000 kJ/kg

Examples:

• R-152a (HFC-152a) - LFL: 0.049 kg/m³
• Some HFO blends

Application requirements:

• Significant charge limitations
• Explosion-proof electrical equipment required in some cases
• Enhanced ventilation mandatory
• Refrigerant detection systems required
• Limited use in occupied spaces

Class 3: Higher Flammability

Criteria:

• Burning velocity > 10 cm/s
• Highly flammable with rapid flame propagation
• Wide flammability range

Examples:

• R-290 (propane) - LFL: 0.038 kg/m³, burning velocity: 46 cm/s
• R-600a (isobutane) - LFL: 0.043 kg/m³
• R-1270 (propylene) - LFL: 0.042 kg/m³

Flammability Properties:

Application requirements:

• Strict charge limitations (typically < 150 g residential)
• Class I, Division 2 or Zone 2 electrical equipment required
• Explosion-proof components in some configurations
• Dedicated ventilation with emergency activation
• Refrigerant leak detection mandatory
• Predominantly factory-sealed systems
• Restricted to specific applications

Safety Group Matrix

Complete ASHRAE 34 Classification Table

Lower Flammability Limit (LFL)

Definition and Significance

The Lower Flammability Limit (LFL) represents the minimum concentration of refrigerant vapor in air that will support combustion when exposed to an ignition source at standard temperature and pressure.

Key relationships:

$$LFL_{kg/m^3} = \frac{LFL_{vol%} \times MW}{24.45}$$

Where:

• LFL_vol% = volumetric concentration (%)
• MW = molecular weight (g/mol)
• 24.45 = molar volume at 25°C, 1 atm (L/mol)

Test Methods

ASTM E681: Standard Test Method for Concentration Limits of Flammability of Chemicals

• Ascending concentration method
• Ignition source at center of 12L spherical vessel
• Temperature: 23°C ± 3°C
• Pressure: 101 kPa ± 2 kPa
• Flame propagation criteria: visible flame spread

LFL Measurement Example

For R-32 (difluoromethane):

• LFL (volumetric): 14.4%
• Molecular weight: 52.02 g/mol
• LFL (mass): (0.144 × 52.02) / 24.45 = 0.307 kg/m³

Safety Factors

Code requirements typically apply safety factors to LFL values:

Refrigerant Charge Limit Calculation:

$$m_{max} = \frac{LFL \times V \times SF}{1000}$$

Where:

• m_max = maximum charge (kg)
• LFL = lower flammability limit (g/m³)
• V = room volume (m³)
• SF = safety factor (typically 0.20 to 0.25 for 2L refrigerants)

Equipment Room Requirements

Machinery Room Classification

Institutional Occupancy (Group I) Requirements:

Equipment rooms containing refrigerants must meet stringent requirements when serving institutional occupancies such as:

• Hospitals and healthcare facilities
• Schools and educational institutions
• Correctional facilities
• Daycare centers

Mandatory features:

1. Dedicated space - no other mechanical equipment permitted
2. Two-hour fire-rated separation from occupied spaces
3. Access limited to authorized personnel
4. Exterior access or access from non-occupied corridor
5. Refrigerant detection with automatic ventilation activation
6. Emergency lighting and exit signage

General Machinery Room Requirements

IBC/IMC Section 1106 and ASHRAE 15 Requirements:

Construction Requirements by Refrigerant Class

Class A1 Refrigerants:

• Standard construction materials acceptable
• One-hour fire rating minimum for critical occupancies
• Adequate ventilation for oxygen displacement prevention

Class A2L Refrigerants:

• One-hour fire-rated construction minimum
• Refrigerant detection required for charges exceeding threshold
• Mechanical ventilation interlocked with detection
• Standard electrical equipment acceptable
• Emergency shutoff accessible from outside room

Class A3 Refrigerants:

• Two-hour fire-rated construction required
• Class I, Division 2 or Zone 2 electrical classification
• Explosion-proof lighting and switches in some cases
• Refrigerant detection mandatory regardless of charge
• Emergency ventilation with automatic activation
• Ignition source controls within 18 in (460 mm) of floor

Class B2L Refrigerants (Ammonia):

• Two-hour fire-rated construction
• Vapor-tight construction on interior side
• Refrigerant detection with two-stage alarm
• Emergency ventilation capable of 30 ACH minimum
• Self-contained breathing apparatus (SCBA) required on-site
• Emergency eyewash and safety shower
• Dedicated exhaust discharge above roof, remote from air intakes

Ventilation Requirements

Normal Ventilation

ASHRAE 15 Section 8.12 - Machinery Room Ventilation:

Minimum ventilation rates based on refrigerant classification:

$$Q_{norm} = \max(0.5 \text{ cfm/ft}^2, \text{ code minimum})$$

For standard machinery rooms:

• Minimum 0.5 cfm/ft² (2.5 L/s·m²) of floor area
• Or per mechanical code (typically 1.0 cfm/ft² for electrical rooms)
• Continuous operation when equipment operating
• May be reduced during unoccupied periods with supervision

Emergency Ventilation

Activation triggers:

• Refrigerant concentration exceeding TLV-TWA
• Manual activation via pull station
• System leak detection alarm
• Loss of normal ventilation

Emergency ventilation rates:

Emergency ventilation calculation for A2L refrigerants:

$$Q_{emerg} = \frac{m_{ref} \times 150}{\rho_{air}}$$

Where:

• Q_emerg = emergency ventilation rate (cfm)
• m_ref = refrigerant charge (lb)
• ρ_air = air density ≈ 0.075 lb/ft³

Example: System with 50 lb R-32 charge: Q_emerg = 50 lb × 150 cfm/lb = 7,500 cfm minimum

Ventilation System Design Features

Supply air:

• High-level introduction (ceiling height)
• Distributed delivery to avoid dead zones
• Tempered when required for comfort
• Isolated from building supply system

Exhaust air:

• Low-level intake for refrigerants heavier than air (most)
• High-level intake for ammonia (lighter than air)
• Direct discharge to outdoors, > 15 ft (4.6 m) from air intakes
• Above roof level or minimum 20 ft (6.1 m) above grade
• Exhaust fan located outside machinery room (not pulling contaminated air through fan)
• Corrosion-resistant construction for B-class refrigerants

Control sequence:

1. Normal ventilation operates continuously during equipment operation
2. Refrigerant detector senses concentration > TLV-TWA
3. First-stage alarm annunciates locally and remotely
4. If concentration exceeds STEL or reaches 25% of LFL (whichever lower):
   • Second-stage alarm activates
   • Emergency ventilation energizes automatically
   • Equipment may be shut down (depending on refrigerant and system)
   • Building management system notification

Refrigerant Detector Requirements

Detection System Specifications

ASHRAE 15 Section 8.12 and IMC 1106:

Refrigerant detection systems required when:

• Any amount of Class B refrigerant in machinery room
• Class A2L refrigerants exceeding charge limits for occupied space
• Class A3 refrigerants in any machinery room application
• Institutional occupancies regardless of refrigerant class

Detector Placement

Number and location of detectors:

$$N_{detect} = \max\left(\frac{A_{floor}}{2500 \text{ ft}^2}, 2\right)$$

Minimum two detectors required regardless of room size.

Placement guidelines:

Strategic locations:

• Near potential leak sources (compressors, valve packages, connections)
• In low air velocity zones where refrigerant may accumulate
• Not in direct airflow from supply or exhaust
• Protected from physical damage
• Accessible for maintenance and calibration

Alarm Setpoints

Two-stage alarm configuration:

Example setpoints for common refrigerants:

*Some jurisdictions require detection for all refrigerants in machinery rooms

Detector Technology

Sensor types by application:

Infrared (IR) sensors:

• Best for: HFCs, HFOs, hydrocarbons
• Advantages: Selective, stable calibration, long life (5-10 years)
• Range: 0-5,000 ppm typical, up to 100% volume for flammable gas
• Response time: < 30 seconds T90

Electrochemical sensors:

• Best for: Ammonia (R-717)
• Advantages: High sensitivity, low cost
• Limitations: 2-3 year sensor life, cross-sensitivity to other gases
• Range: 0-100 ppm (low level), 0-1,000 ppm (high level)
• Response time: < 60 seconds T90

Catalytic bead sensors:

• Best for: Hydrocarbon refrigerants (A3 class)
• Advantages: Direct measurement of flammability
• Range: 0-100% LFL
• Limitations: Requires oxygen present, can be poisoned
• Response time: < 30 seconds T90

Maintenance and Calibration

Required maintenance schedule:

Calibration procedure:

1. Apply known concentration reference gas
2. Verify alarm setpoint activation
3. Verify remote alarm transmission
4. Test emergency ventilation interlock
5. Document results with date, technician, and gas concentration used

Refrigerant Concentration Limits (RCL)

RCL Calculation Methodology

ASHRAE 15 Section 7 - Refrigerant Concentration Limits:

The RCL represents the maximum allowable concentration of refrigerant vapor in occupied spaces based on toxicity and flammability considerations.

For Class A1 refrigerants (non-flammable):

$$RCL = \min(OEL, ODL)$$

Where:

• OEL = Occupational Exposure Limit (ppm)
• ODL = Oxygen Deprivation Limit (typically 52,000 ppm or 5.2% volume)

For Class 2L refrigerants:

$$RCL = \min\left(OEL, \frac{LFL}{4}, ODL\right)$$

The factor of 4 provides safety margin below flammability limit.

For Class 3 refrigerants:

$$RCL = \min\left(OEL, \frac{LFL}{4}\right)$$

More restrictive due to higher flammability hazard.

Maximum Charge Calculations

Based on room volume:

$$m_{max} = \frac{RCL \times V \times MW}{24.04 \times 1000}$$

Where:

• m_max = maximum refrigerant charge (kg)
• RCL = refrigerant concentration limit (ppm volume)
• V = room volume (m³)
• MW = molecular weight (g/mol)
• 24.04 = molar volume at 20°C, 101.3 kPa (L/mol)

Example calculation for R-32 in residential space:

Given:

• Room volume = 50 m³
• R-32 LFL = 14.4% volume = 144,000 ppm
• MW = 52.02 g/mol
• RCL = 144,000/4 = 36,000 ppm (flammability basis)
• OEL = 1,000 ppm (toxicity basis)

RCL = min(1,000, 36,000, 52,000) = 1,000 ppm (toxicity controls)

Maximum charge: m_max = (1,000 × 50 × 52.02) / (24.04 × 1000) = 108.2 kg

However, practical charge limits from standards are more conservative.

ISO 817 Classification

International Harmonization

ISO 817: Refrigerants - Designation and Safety Classification

Provides international framework complementary to ASHRAE 34:

• Similar safety group structure (A/B toxicity, 1/2/3 flammability)
• Harmonized test methods with ASHRAE
• Referenced by international equipment standards (ISO 5149)
• Adopted by European standards (EN 378)

Key Differences from ASHRAE 34

Both standards maintain close coordination to ensure global consistency.

Oxygen Deprivation Risk

Mechanism and Consequences

Refrigerants heavier than air can displace oxygen in enclosed spaces, creating asphyxiation hazard even for non-toxic refrigerants.

Oxygen concentration effects:

Oxygen Deprivation Limit (ODL)

ASHRAE 15 establishes minimum oxygen concentration of 19.5% by volume, corresponding to maximum refrigerant concentration of approximately 52,000 ppm (5.2%) for typical refrigerants.

Critical spaces for oxygen deprivation:

• Basements and below-grade equipment rooms
• Vaults and confined spaces
• Walk-in coolers and freezers
• Shipping containers
• Vehicle cargo areas

Mitigation strategies:

1. Adequate ventilation (natural or mechanical)
2. Oxygen monitoring in addition to refrigerant detection
3. Charge limits based on room volume
4. Warning signs at room entrance
5. Confined space entry procedures

Decomposition Products

Thermal Decomposition

Refrigerants exposed to high temperatures (flames, electrical arcs, hot surfaces > 250°C) can decompose into toxic byproducts.

Common decomposition products:

Hydrogen Fluoride (HF) Hazard

Hydrogen fluoride is the primary decomposition product of concern for fluorinated refrigerants:

Properties:

• Highly corrosive to all tissues
• IDLH: 30 ppm
• TLV-TWA: 0.5 ppm (ceiling limit: 2 ppm)
• Penetrates skin rapidly, causes deep tissue burns
• Interferes with calcium metabolism

Detection:

• Characteristic pungent odor (detectable at 0.04 ppm)
• Acid-sensitive paper or detector tubes
• Etching of glass surfaces
• Electronic HF monitors for critical applications

Prevention measures:

1. Avoid open flames in refrigerant-containing spaces
2. Use properly rated electrical equipment
3. Prohibit smoking in machinery rooms
4. Implement hot work permits with refrigerant purging
5. Maintain surface temperatures below decomposition threshold

Emergency Response

Exposure to decomposition products:

1. Evacuate affected area immediately
2. Don self-contained breathing apparatus (SCBA)
3. Remove contaminated clothing
4. Flush exposed skin/eyes with water for 15+ minutes
5. Administer calcium gluconate gel for HF exposure (if trained)
6. Seek immediate medical attention
7. Ventilate area thoroughly before re-entry

Application Guidelines by Safety Class

A1 Refrigerants (Unrestricted)

Permitted applications:

• All occupancy types without restriction
• Residential, commercial, industrial, institutional
• Indoor and outdoor installations
• No charge limits based on flammability (volume limits apply)

Minimal safety requirements:

• Standard electrical equipment
• Adequate ventilation for oxygen displacement only
• Machine room requirements per ASHRAE 15 for large systems
• Standard leak detection (if any) for environmental compliance

A2L Refrigerants (Limited Flammability)

Permitted applications:

• Residential HVAC systems with charge limits
• Commercial comfort cooling and heating
• Refrigeration systems in commercial buildings
• Limited use in institutional occupancies

Charge limits and safety measures:

Detection thresholds:

• Required if refrigerant charge exceeds limits based on smallest occupied space volume
• Must activate emergency ventilation at 25% LFL
• Interface with building fire alarm system

A3 Refrigerants (High Flammability)

Restricted applications:

• Small factory-sealed appliances (< 150 g charge residential)
• Commercial refrigeration with approved safety features
• Industrial process refrigeration in controlled environments
• Outdoor installations with proper separation

Mandatory safety features:

• Factory-sealed system or approved field-serviceable design
• Leak detection interlocked with electrical disconnect
• Explosion-proof equipment within 18 in of potential leak sources
• Enhanced ventilation with emergency activation
• Charge minimization strategies (distributed systems, secondary loops)
• No ignition sources within refrigerant containment zone

Prohibited applications:

• Institutional occupancies (schools, hospitals, prisons)
• High-rise residential buildings (above 75 ft / 23 m)
• Public assembly spaces without engineered safeguards

B2L Refrigerants (Ammonia - Special Case)

Permitted applications:

• Industrial refrigeration (food processing, cold storage)
• Ice rinks and large recreational facilities
• District cooling plants
• Limited commercial supermarket applications with engineered safeguards

Mandatory safety requirements:

• Dedicated machinery room with two-hour fire rating
• Minimum 30 ACH emergency ventilation
• Dual-stage leak detection (25 ppm and 150 ppm typical)
• Self-contained breathing apparatus (SCBA) on-site
• Emergency shower and eyewash station
• Process Safety Management (PSM) program if > 10,000 lb threshold
• Risk Management Plan (RMP) if > 10,000 lb threshold
• Regular safety training for all personnel
• Emergency response plan and coordination with local fire department

Prohibited applications:

• Direct systems serving occupied spaces
• Residential applications
• Most commercial HVAC applications
• Installations without trained maintenance personnel

Regulatory Framework

Key Standards and Codes

ASHRAE Standards:

• ASHRAE 15: Safety Standard for Refrigeration Systems - primary installation standard
• ASHRAE 34: Designation and Safety Classification of Refrigerants - classification basis

Building Codes:

• International Mechanical Code (IMC) Section 1106: Refrigeration systems
• International Building Code (IBC) Section 606: Hazardous materials storage
• International Fire Code (IFC) Chapter 60: Hazardous materials storage and use

Occupational Safety:

• OSHA 29 CFR 1910.119: Process Safety Management (ammonia > 10,000 lb)
• OSHA 29 CFR 1910.146: Confined space entry
• OSHA 29 CFR 1910.134: Respiratory protection

Environmental:

• EPA 40 CFR Part 82: Protection of stratospheric ozone (refrigerant management)
• EPA Section 608: Technician certification requirements
• EPA Section 609: Motor vehicle air conditioning requirements

Compliance Responsibilities

Design professionals:

• Specify appropriate refrigerant safety class for application
• Design systems meeting charge limits or machinery room requirements
• Provide detection and ventilation systems as required
• Ensure compliance with accessibility and egress requirements

Installing contractors:

• Install per approved drawings and manufacturer instructions
• Provide proper refrigerant piping materials and protection
• Install detection and safety systems per specifications
• Perform pressure testing and evacuation procedures
• Document refrigerant charge and system information

Building owners:

• Maintain detection and ventilation systems in operable condition
• Ensure regular calibration and testing per ASHRAE 15
• Provide technician access to machinery rooms
• Maintain system logs and service records
• Ensure only certified technicians service systems

Service technicians:

• Maintain EPA Section 608 or 609 certification
• Follow proper recovery, recycling, and reclamation procedures
• Report refrigerant releases per EPA requirements
• Test and calibrate safety systems during service
• Maintain service logs

Summary

Refrigerant safety classification under ASHRAE Standard 34 provides a systematic framework for evaluating and managing refrigerant hazards based on toxicity and flammability characteristics. The two-character alphanumeric system enables consistent application of code requirements, equipment room design, ventilation systems, and detection protocols appropriate to each refrigerant’s hazard profile.

Key principles:

1. Classification determines requirements: A1 refrigerants face minimal restrictions; A2L, A3, and B-class refrigerants face progressively stricter controls
2. Multiple hazards assessed: Both toxicity (via OEL) and flammability (via LFL and burning velocity) inform safety classification
3. Defense in depth: Charge limits, detection, ventilation, and equipment room construction provide layered protection
4. Application-specific: Requirements scale based on occupancy type, system size, and installation location
5. Evolving landscape: New lower-GWP refrigerants (particularly A2L class) require updated design practices

Proper understanding and application of refrigerant safety classifications ensures code-compliant installations that protect building occupants, service personnel, and first responders from refrigerant-related hazards.