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Design Considerations for Special Hazard Fire Suppression

For engineers, facility managers, EHS leaders, and project teams building or renovating critical rooms, data centers, control rooms, archives, labs, electrical rooms, and other special hazards where water damage and downtime are unacceptable.

At a Glance

  • A clean agent or inert gas system only performs if the enclosure can hold agent concentration long enough to stop the fire and prevent re-ignition.
  • The most common failures are not hardware failures, they are room, HVAC, and control integration failures.
  • Use this page as a practical design checklist, then coordinate architecture, mechanical, electrical, and life safety interfaces before installation.
  • Systems referenced: SF-1230 / FK-5-1-12, ProInert2 inert gas, ECARO-25, and FM-200.

Step One, Understand the Hazard You Are Protecting

Every special hazard design starts with the hazard, not the agent. The fuel type, room use, occupancy, and criticality determine detection strategy, design concentration, discharge sequence, and the best suppression approach.

Common hazard classes in special hazard rooms

  • Class A: ordinary combustibles, paper, cardboard, cable insulation, furniture, and building finishes.
  • Class B: flammable and combustible liquids, fuels, lubricants, and some process chemicals.
  • Class C: energized electrical equipment, server racks, UPS systems, motor control centers, and process controls.

Hazard classification influences design concentration and the decision between chemical clean agents and inert gas systems. For a broader overview, visit Clean Agent Fire Suppression.

Architectural Considerations, Build the Right Room

Room integrity is one of the most critical and most overlooked parts of any gaseous suppression design. If the room leaks, the system can discharge correctly and still fail to maintain the required concentration.

Architectural checklist

  1. Perimeter walls are full height to the structural deck or next solid barrier, not stopping at a drop ceiling.
  2. For subfloor applications, bulkheads isolate suppression zones and prevent agent bypassing the protected volume.
  3. Access doors to protected areas have door seals, sweeps, and automatic closures to limit leakage during discharge.
  4. Penetrations for cables, conduit, piping, and sleeves are sealed using appropriate sealing and firestopping methods.

If you need deeper guidance on enclosure tightness and practical sealing methods, review Proper Sealing of Clean Agent Rooms and Clean Agent Room Integrity Testing and Sealing.

Fast reality check, if any of these are true, expect performance risk

  • Above-ceiling space is used as a return plenum and is tied into the building air system.
  • The room has frequent cable adds and penetrations that are not sealed immediately.
  • Doors are not self-closing, or are commonly propped open for operations.
  • Raised floor and subfloor boundaries are not defined and bulkheaded.

Mechanical Considerations, HVAC and Airflow Control

Mechanical systems directly affect whether a clean agent discharge will stay in the room long enough to be effective. Conditioned air, return paths, economizers, and make-up air must be controlled so they do not carry agent away from the hazard.

What to coordinate during design

  • Any supply or return air from the building system should use motor operated dampers for closure upon the control system second alarm.
  • Dampers become especially important when the above-ceiling area is used as a return air plenum tied into the building air system.
  • Coordinate damper locations and control wiring with the fire suppression control panel early, not after installation.
  • Consider dedicated computer room air conditioning (CRAC) units, economizers, and make-up air systems that can dilute or exhaust agent.
  • Plan post-discharge exhaust or purge systems if required by local codes or owner standards, and sequence them so they do not remove agent too quickly.

Electrical Considerations, Power and Control Interfaces

Electrical design is more than supplying power to a releasing panel. The system must interconnect correctly with HVAC, emergency power off, and the building life safety system so alarms, shutdowns, and reporting operate safely and as required.

Electrical and control checklist

  1. If computer equipment requires an emergency power off switch, tie it into the control panel via dry contact so power can be removed as part of the suppression sequence.
  2. Dedicated air units and dampers should be interconnected for shutdowns with the control panel, with interconnection power independent of the control panel and located within their own enclosures.
  3. Provide a 120 VAC power circuit through a dedicated 20 amp circuit breaker to the releasing control panel, pre-action air compressor, and VESDA power supply where applicable.
  4. Coordinate interconnection between the suppression control panel and building life safety system for correct alarm, supervisory, and trouble reporting based on local requirements.

When integrating advanced detection technologies such as aspirating detection, SSI coordinates placement, power requirements, and signal interfaces. See VESDA Aspirating Smoke Detection and Fire Alarms and Detection Systems.

Unique Design Considerations for Modern Facilities

Many special hazard rooms include features that change how gas fills a space and how long it stays at the required concentration. If your design assumes a simple open room, you can miss the real airflow and compartment behavior.

Modern features that matter

  1. Hot aisle and cold aisle containment in data centers, changing airflow patterns and creating partial barriers inside the protected volume.
  2. External humidification systems, adding penetrations and airflow paths that impact leakage and concentration.
  3. Continual mixing or HVAC systems that run continuously, diluting agent if not properly shut down on release.
  4. Exhaust purge systems that must be sequenced carefully so agent is not removed too quickly after discharge.

SSI reviews these features early so suppression performance, detection layout, and mechanical controls operate as a coordinated system.

Calculating Agent Quantities, Volume, Environment, and Safety

Clean agent and inert gas systems are engineered solutions. Each design is based on calculations of agent quantity, nozzle layout, and discharge time using manufacturer data and applicable standards.

Design inputs that drive agent quantity

  • Room volume, length x width x height, adjusted for mezzanines, subfloors, soffits, and significant solid obstructions.
  • Altitude and temperature, performance and storage pressure can change with elevation and ambient conditions.
  • Design concentration, required percentage by volume for the selected agent and hazard class.
  • Occupancy safety, designs should remain within published NOAEL and LOAEL guidance for occupied spaces.
Engineered ECARO-25 clean agent cylinder bank for special hazard protection

SSI uses manufacturer approved tools, hydraulic flow methods, and field experience to size cylinder banks so the correct quantity reaches every nozzle within the required time window.

Piping and Hydraulic Flow, Delivering Agent Where It Is Needed

The piping network delivers agent from cylinders to the hazard. Hydraulic design ensures the farthest nozzle receives the correct flow within the required discharge window.

Key piping and discharge considerations

  • Clean agent systems are typically designed for a discharge time of 10 seconds, inert gas systems often use a longer discharge window per applicable standards.
  • Pipe sizes, fitting types, and elevation changes affect pressure loss and flow, and must be captured in the design calculation.
  • Nozzle locations and orifice sizes should promote uniform distribution without excessive noise or drafts that could disturb sensitive equipment.

If you are also evaluating non-clean-agent options for special hazards, see ProInert2 Inert Gas Fire Suppression and Specialty Water Suppression Systems.

Codes, Standards, and Industry Guidance

Special hazard fire suppression designs must comply with multiple codes and standards. SSI designs systems to applicable NFPA standards and manufacturer manuals, and coordinates with local AHJ expectations during design and acceptance.

Common standards referenced for special hazards

For legacy HFC based systems and regulatory context, see AIM Act and HFC Phasedown.

Acceptance Testing, Commissioning, and Turnover

Successful turnover depends on proving the system as a whole, enclosure integrity, HVAC shutdown sequence, detection performance, releasing logic, notification, and reporting. If you treat those as separate scopes, you will find the gaps at the worst possible time.

Pre-test checklist that prevents late rework

  • Final room boundaries are defined, penetrations are sealed, and doors are equipped with seals and sweeps.
  • Dampers close on second alarm as designed, and shutdowns are verified under the releasing sequence.
  • All interlocks are functional, including EPO where required, and building fire alarm reporting signals are verified.
  • Nozzles and piping match the engineered design and calculation, with correct orifices installed.
  • Room integrity testing is planned when required by project objectives, owner standards, or AHJ direction.

FAQ, Questions Industrial Teams Actually Ask

Why do clean agent systems fail acceptance testing

The most common reasons are enclosure leakage, uncontrolled HVAC paths, missing damper interlocks, and incomplete signal integration with life safety systems. The hardware can be correct while the room and sequence are not.

Do I need motor operated dampers for a clean agent room

If building supply or return air can move agent out of the protected volume, dampers and shutdown logic are often required to contain agent during discharge and hold time. They are especially important when above-ceiling return plenums are tied into the building air system.

What is the biggest design mistake in special hazard rooms

Treating the room like a normal space with normal HVAC behavior. Special hazards need an engineered enclosure boundary and an engineered sequence of operation, or performance becomes unpredictable.

How do I choose between clean agent and inert gas

It depends on the hazard class, occupancy profile, environmental goals, and enclosure constraints. SSI designs both and can align the solution to the room, codes, and long-term operational reality. Start with Clean Agents and ProInert2.

Why Partner With Suppression Systems, Inc. for Special Hazards

Finding the right fire protection solutions is something SSI has been doing since 1983. Special hazard work is won or lost in the details, enclosure integrity, airflow control, and control integration, not just selecting an agent.

  • NICET certified designers and project managers focused on special hazards.
  • In-house CAD, hydraulic modeling, and agent flow calculations.
  • Experience with clean agents, inert gas, carbon dioxide, and specialty water systems.
  • Support for new construction and retrofits of existing systems.
  • Coverage across Pennsylvania, New Jersey, New York, Delaware, Maryland, and surrounding regions.

Service Area Focus

SSI is headquartered in Breinigsville, Pennsylvania and supports special hazard fire suppression projects across the East Coast region within practical travel distance for engineering support, commissioning, and long-term service.

Talk to SSI About Your Special Hazard Room

If you are designing, building, or renovating a special hazard room, contact SSI early. Early coordination prevents late-stage rework, failed acceptance tests, and performance uncertainty when a discharge happens.

To speed up design review, send room use, approximate dimensions, ceiling type, whether above-ceiling is a return plenum, HVAC paths, raised floor details, and any planned containment or humidification systems.

Related SSI Pages

Suppression Systems, Inc., 155 Nestle Way, Suite 104, Breinigsville, PA 18031.