The temperature in the computer room is being increased from 18°C/64°F to 27°C/81°F. What is the impact, if any, on the amount of gas required to suppress a fire assuming the gas is a Halocarbon?

The amount of Halocarbon gas required for a total flooding fire suppression system is calculated based on achieving a specific design concentration (a percentage of volume). The formula for the required weight (W) of the agent is inversely proportional to its specific volume (S), as defined in standards like NFPA 2001. The specific volume of a gas is the volume occupied by a unit of its mass. According to the gas laws, as the temperature of a gas increases, it expands, meaning its specific volume increases. Therefore, at the higher temperature of 27°C, less mass of the Halocarbon agent is needed to expand and achieve the required volumetric concentration to suppress a fire in the fixed-volume room.

A. The amount of gas required will be higher: This is incorrect. A higher temperature increases the specific volume of the gas, meaning less mass is required to achieve the target concentration by volume.
B. The amount of gas required will not change: This is incorrect. The physical properties of the gas, specifically its specific volume, are directly dependent on temperature, which directly impacts the required mass.
D. The change to the amount of gas cannot be determined without knowing the change in humidity as well: This is incorrect. While humidity affects air properties, the standard calculation for the required agent mass is primarily a function of room volume, agent concentration, and temperature.

1. NFPA 2001: Standard on Clean Agent Fire Extinguishing Systems (2022 Edition).

Section 5.5.2, "Total Flooding Quantity." This section provides the formula for calculating the weight of the agent: W = (V/S) × [C / (100 – C)].

Section 5.5.2.3. This section defines the formula for the specific volume (S) of the agent vapor as S = k1 + k2(t), where 't' is the temperature. The constants (k1, k2) for Halocarbons are such that S increases with temperature. Since S is in the denominator of the weight formula, an increase in temperature 't' results in a decrease in the required weight 'W'.

2. SFPE (Society of Fire Protection Engineers), SFPE Handbook of Fire Protection Engineering, 5th Edition.

Chapter 59, "Halogenated Agent Halon-Alternative Extinguishing Systems." Section 59.4.1, "Total Flooding System Design," explains the calculation methods which are based on NFPA 2001. It confirms that the agent quantity is determined for the minimum anticipated temperature, as this represents the worst-case scenario requiring the most agent. This directly implies that higher temperatures require less agent. (DOI: https://doi.org/10.1007/978-1-4939-2562-459)

3. Fike Corporation, ECARO-25® (HFC-125) Clean Agent Fire Suppression System Design, Installation, Operation, and Maintenance Manual.

Section 3, "System Design." This official vendor manual, which adheres to NFPA 2001 standards, provides the same temperature-dependent formulas for calculating agent weight. The design examples consistently show that the lowest expected temperature in the hazard area must be used for calculations, as this condition requires the largest amount of agent.