How to connect fire protection to the cold aisle of the computer room

Effective fire protection in a cold aisle requires integrating suppression and detection systems with the aisle's containment while considering airflow, nozzle placement, and agent type.

Understanding Cold Aisle Containment

Cold aisle containment (CAC) isolates the intake side of server racks to optimize cooling efficiency. The cold air is directed through the aisle, while hot air is exhausted to the hot aisle. This containment improves energy efficiency but can alter fire suppression dynamics, as enclosed spaces may concentrate flames and affect agent distribution if not properly designed.

Fire Detection Strategies

Aspirating Smoke Detection (HSSD/VESDA): High airflow in cold aisles can dilute smoke, delaying detection by conventional ceiling detectors.

VESD

A systems draw air through sampling pipes along the aisle, detecting smoke early before it spreads. Sampling points should be placed in the cold aisle, hot air return ducts, and cabinet interiors for comprehensive coverage. Ceiling and Return Air Sampling: For fires outside the aisle, ceiling sampling points or return air grilles of CRAHs can detect smoke effectively.

Fire Suppression Approaches

Clean Agent Systems: Preferred for IT equipment as they chemically interfere with combustion or reduce oxygen without damaging electronics. The aisle should be treated as an enclosed space, similar to floor or ceiling voids, to ensure homogeneous agent distribution. Nozzle Placement: Optimal location is typically centered along the longest wall of the cold aisle, with at least 1.

2 meters clearance on all sides of the nozzle discharge pattern. Obstructions near the nozzle may require additional agent to maintain effective concentration. For halocarbon agents, ensure horizontal and frontal clearance to avoid uneven coverage.

Pressure Management: Contained aisles can experience pressure effects during gas discharge. Use pressure relief vents and proper capacity sizing to prevent damage to infrastructure and IT equipment. Integration with Sprinklers: In some cases, FM-approved drop-away panels allow sprinklers to protect the building while clean agents protect the aisle.

Ensure spray patterns reach all areas of the aisle, considering obstructions and containment barriers.

Material Considerations

Containment barriers should be noncombustible where possible (metal or tempered glass). Rigid Class A plastics with low Smoke Developed Index (SDI ≤ 120) are recommended for translucent panels. Avoid flexible plastics that ignite easily and produce contaminating smoke.

Best Practices

Treat the cold aisle as a semi-enclosed enclosure for both detection and suppression design. Coordinate airflow, detection, and suppression early in the project to ensure integration with cooling systems.

Follow NFP

A 75 and BS EN 15004 standards for nozzle placement, agent concentration, and detection coverage. Regularly inspect and maintain both detection and suppression systems to ensure effectiveness in high-airflow environments. By carefully integrating detection and suppression systems with the cold aisle, considering airflow, nozzle placement, and containment materials, you can maximize fire safety without compromising cooling efficiency in your computer room.