Fire Safety Engineering

Fire safety engineering integrates HVAC system design with life safety objectives to control smoke movement, maintain tenable conditions during evacuation, and prevent fire spread through building air distribution systems. HVAC systems play a critical role in occupant safety during fire events through smoke control, compartmentation, and pressurization strategies.

Smoke Control System Design

Smoke control systems manage smoke movement during fire events to protect egress paths and designated refuge areas. Design approaches depend on building geometry, occupancy classification, and code requirements.

Smoke Control Methods

Pressurization Systems

Stairwell pressurization: 0.10-0.15 in. w.g. minimum pressure differential
Elevator shaft pressurization: 0.05-0.10 in. w.g. across closed doors
Vestibule pressurization: series pressurization for enhanced protection
Zoned smoke control: pressure differential zoning with barriers

Smoke Exhaust Systems

Dedicated smoke exhaust fans with temperature-rated construction
Exhaust rates: 4-6 air changes per hour for smoke zones
Makeup air provisions: 50-100% of exhaust air volume
Smoke reservoir design: minimum 20% of floor-to-ceiling height

Design Pressure Differentials

Application	Minimum Pressure	Maximum Pressure	Design Basis
Stairwell (doors closed)	0.10 in. w.g.	0.35 in. w.g.	NFPA 92A
Stairwell (single door open)	0.05 in. w.g.	–	Maintain flow direction
Elevator shaft	0.05 in. w.g.	0.20 in. w.g.	Stack effect mitigation
Refuge area	0.05 in. w.g.	0.25 in. w.g.	Positive pressure
Smoke zone boundary	0.05 in. w.g.	0.15 in. w.g.	Zone isolation

Tenability Criteria

Maintain tenable conditions in protected areas:

Visibility: greater than 30 ft (10 m) in egress paths
Temperature: below 140°F (60°C) at head height
Carbon monoxide: less than 1,400 ppm for 30-minute exposure
Oxygen concentration: greater than 15% by volume
Smoke layer height: minimum 6 ft (1.8 m) above floor level

Fire and Smoke Dampers

Fire dampers and smoke dampers prevent fire and smoke propagation through air distribution systems where ductwork penetrates fire-rated assemblies.

Fire Damper Requirements

Installation Locations

Duct penetrations through fire-rated walls (1-hour minimum)
Duct penetrations through fire-rated floor/ceiling assemblies
Corridor wall penetrations in non-sprinklered buildings
Shaft penetrations (except by specific code exceptions)

Fire Damper Classifications

Damper Type	Closure Temperature	Fire Rating	Typical Application
Static fire damper	165°F (74°C)	1.5 or 3 hours	Fire walls, area separation
Dynamic fire damper	165°F (74°C)	1.5 or 3 hours	Operating air systems
Ceiling radiation damper	165°F (74°C)	1 or 2 hours	Membrane penetrations
Combination fire/smoke	165°F (74°C)	1.5 or 3 hours	Dual function applications

Fusible Link Ratings

Standard rating: 165°F (74°C) for typical applications
Intermediate rating: 212°F (100°C) for high ambient areas
High rating: 286°F (141°C) for commercial kitchens or boiler rooms

Smoke Damper Requirements

Operational Characteristics

Closure actuation: smoke detector signal or fire alarm system
Leakage classification: Class I (10 cfm/ft²), Class II (40 cfm/ft²), Class III (120 cfm/ft²)
Temperature rating: 250°F (121°C) minimum for smoke dampers
Elevated temperature rating: 350°F (177°C) for combination dampers

Installation Standards

Code Requirement	Application	Actuation Method	Leakage Class
NFPA 90A	Air distribution systems	Smoke detector	Class I or II
NFPA 105	Smoke barrier penetrations	Fire alarm signal	Class I
IBC Section 717	Shaft penetrations	Area smoke detector	Class II
IMC Section 607	Corridor penetrations	Duct smoke detector	Class II

NFPA Code Requirements

NFPA 90A: Air Conditioning and Ventilating Systems

Duct System Protection

Duct smoke detectors required for systems exceeding 2,000 cfm
Detector locations: downstream of filters, upstream of branch connections
Fan shutdown sequence: within 60 seconds of detector activation
Outside air intake closure: smoke dampers at outdoor air intakes

Duct Construction and Materials

Fire-rated duct systems through fire-rated shafts
Noncombustible or limited-combustible materials
Duct insulation flame spread index: 25 maximum
Smoke developed index: 50 maximum

NFPA 92: Smoke Control Systems

Design Documentation Requirements

Rational analysis based on physical principles
Computational fluid dynamics (CFD) modeling for complex geometries
Full-scale acceptance testing procedures
Operations and maintenance manuals

System Performance Testing

Test Parameter	Acceptance Criteria	Test Method
Pressure differential	±20% of design value	Differential pressure gauge
Airflow volume	±10% of design value	Pitot tube traverse
Door opening force	≤30 lbf (133 N)	Force gauge at latch
Smoke detector response	Alarm within 30 seconds	Canned smoke test
Damper closure time	≤60 seconds	Visual observation
Fan start time	≤30 seconds	Control system verification

NFPA 101: Life Safety Code

Smoke Compartmentation

Maximum smoke compartment area: 22,500 ft² (2,090 m²)
Maximum travel distance to smoke barrier: 200 ft (61 m)
Smoke barrier rating: 1-hour minimum
HVAC system isolation across smoke barriers

Integration with Fire Alarm Systems

Control Sequences

Fire Alarm Activation Response

Shut down air handling units serving fire zone
Close smoke dampers in smoke barrier penetrations
Activate smoke control pressurization fans
Override economizer controls to 100% outdoor air (if applicable)
Disable variable air volume box minimum flow setpoints
Release magnetic hold-open devices on fire doors

Interface Requirements

Hard-wired connections between fire alarm panel and HVAC controls
Dedicated fire alarm circuits (non-multiplexed)
Supervised circuit monitoring with trouble indication
Manual override capability at fire command center
Annunciation of smoke control system status

Duct Smoke Detector Integration

Detector Placement

Return air systems: prior to air entering return air plenum
Supply air systems: downstream of fan, upstream of first branch
Detector sampling tube velocity: 200-1,500 fpm
Maximum detector spacing: per manufacturer’s listing

Control Actions

Detector Location	Primary Action	Secondary Action	Override Capability
Return air duct	Shut down fan	Close outdoor air damper	Fire department only
Supply air duct	Shut down fan	Activate alarm	Fire department only
Smoke control zone	Activate pressurization	Close zone dampers	Automatic by system
Elevator lobby	Recall elevators	Pressurize shaft	Manual at fire panel

Pressurization System Design

Stairwell Pressurization

Supply Air Calculations

Door leakage component: Q_door = 60 A√(ΔP)
Construction leakage: Q_wall = 0.2 cfm/ft² at design pressure
Minimum airflow: sum of all leakage paths with safety factor
Relief damper sizing: accommodate single door opening scenario

Fan Selection Criteria

Multiple fan speeds or VFD control for door opening compensation
Pressure rise: 1.5-2.0 in. w.g. at design flow
Temperature rating: 250°F (121°C) for 1 hour minimum
Redundant fan configuration for critical facilities

Zoned Smoke Control

Pressure Zoning Strategy

Fire zone: negative pressure (exhaust)
Adjacent zones: neutral or slight positive pressure
Remote zones: normal HVAC operation
Vertical shafts: positive pressure relative to fire floor

Makeup Air Requirements

Exhaust Rate (cfm)	Makeup Air Source	Distribution Method	Temperature Control
10,000-30,000	Dedicated fan	Low-level discharge	Heated to 65°F min
30,000-75,000	Multiple fans	Perimeter distribution	Heated or tempered
>75,000	Centralized MUA unit	Overhead distribution	Full heating capacity

Fire-Rated Construction

Fire Resistance Requirements

Ductwork in Fire-Rated Assemblies

2-hour shaft: 2-hour duct or dampers at entry/exit
1-hour shaft: 1-hour duct or dampers at entry/exit
Fire barrier penetration: damper with equal rating to barrier
Grease duct in shaft: may require additional protection

Shaft Penetration Protection

Shaft Rating	Duct Protection Method	Damper Requirement	Inspection Access
2-hour	2-hour duct system	Not required if duct rated	Every floor
2-hour	Unprotected duct	1.5-hour damper both ends	At penetration
1-hour	1-hour duct system	Not required if duct rated	Every floor
1-hour	Unprotected duct	1.5-hour damper both ends	At penetration

Kitchen Exhaust Systems

Grease Duct Fire Protection

Duct material: 16 gauge (1.5 mm) carbon steel minimum
Clearance to combustibles: 18 in. (450 mm) minimum
Fire suppression system: actuation closes supply air dampers
Exhaust fan interlock: continues operation during suppression

Testing and Commissioning

Fire Damper Testing

Installation Verification

Sleeve alignment with structural opening
Clearance for full blade travel without interference
Fusible link orientation and temperature rating
Access door location for inspection and testing

Operational Testing

Drop test: manual release of fusible link mechanism
Closure verification: complete seating of blades
Airflow impact: minimal pressure drop when open
Reset procedure: proper blade return and link replacement

Smoke Control System Commissioning

Pre-functional Checks

Verify all dampers installed per design drawings
Confirm pressure sensor calibration and location
Test all duct smoke detectors with canned smoke
Verify control sequence programming against specifications
Inspect air distribution pathways for obstructions

Functional Performance Tests

Measure pressure differentials at design conditions
Verify door opening forces at all egress points
Confirm smoke detector activation response times
Document fan performance (flow, pressure, power)
Test manual override functions at fire command center
Conduct system performance under simulated fire scenarios

Acceptance Criteria Verification

System Component	Performance Metric	Tolerance	Corrective Action Threshold
Pressure differential	Design ΔP	±20%	Adjust fan speed or relief damper
Airflow rate	Design cfm	±10%	Rebalance distribution system
Door opening force	30 lbf maximum	+0 lbf	Reduce pressure or add relief
Detector response	30 seconds	±5 seconds	Relocate or adjust sensitivity
Fan start delay	30 seconds	±10 seconds	Reprogram control sequence

Documentation Requirements

Design Documentation

Submittal Documents

Smoke control system narrative and design basis
Pressure differential calculations with leakage assumptions
Smoke exhaust and makeup air sizing calculations
Fire damper schedule with ratings and locations
Duct smoke detector locations and wiring diagrams
Control sequence of operations for all fire modes

Operations and Maintenance

Required Information

System description and operational theory
Inspection and testing schedules (annual minimum for dampers)
Troubleshooting procedures and common failure modes
Replacement parts list with manufacturer contact information
As-built drawings showing final installation conditions
Commissioning test results and acceptance documentation

Fire safety engineering requires comprehensive integration between HVAC systems, fire protection systems, and building codes to ensure life safety objectives are achieved during fire events.

Sections

Smoke Control Systems

Components

Pressurization Systems
Mechanical Smoke Exhaust
Natural Smoke Venting
Atrium Smoke Control
Stairwell Pressurization
Elevator Shaft Pressurization
Smoke Control Sequence

Fire Damper Systems

Components

Fire Damper Rating Requirements
Combination Fire Smoke Dampers
Ceiling Radiation Dampers
Fusible Link Actuation
Electric Actuator Dampers
Fire Damper Inspection Requirements
Imc Nfpa Requirements

Fire Resistance Rated Assemblies

Components

Ul Rated Floor Ceiling
Ul Rated Wall Assemblies
Penetration Firestopping
Through Penetration Firestop Systems
Membrane Penetration Firestop