Compartment Fire Assessment

Objective:

To determine the effect of ventilation on fire severity.

Apparatus:

The apparatus consists of a test chamber with internal dimensions of 630mm wide, 580mm high and 600mm deep with a 550mm high adjustable door opening (See figure 5.0) A load cell is positioned centrally but 90mm above chamber floor level. Metal fuel trays are provided.

heights from the ceiling.

Top thermocouple 50 mm from ceiling,

Middle thermocouple 150 mm from ceiling,

Low thermocouple 250 mm from ceiling.

The thermocouple and load cell are attached to a computer data logging system.

Note: Load cell requires calibration of voltage to mass:

Theory:

The fire temperature variation with time can be determined from a heat balance for the enclosure under consideration taking into account the heat produced by fuel (in the form of combustible materials) and heat losses to enclosure boundaries and through the opening.

The temperature course of fires can vary widely. The two most important factors controlling this variation and the fire load plus the size and shape of the opening through which air necessary for combustion can enter. A typical enclosure fire growth curve is shown in Figure 5.1.

These variations can control the maximum temperature of the fire gases within the enclosure and the duration of the fire.

This experiment examines typical temperature/ mass loss versus time variations when the opening factor is varied.

Procedure:

• Locate the thermocouple and load cell instruments and ensure they are correctly connected to the data logging equipment,
• Set in a tray of methylated spirits (200ml),
• Set the opening to a fixed value. (fully open to begin with),
• Initialise the data recording devices,
• Light taper provided and carefully ignite the fuel whilst simultaneously starting the recording devices,
• Pay close attention to the pattern of burning within the enclosure and note the time when flames start to emerge from the opening. This will denote the onset of flashover.

Repeat the experiment with different opening widths (e.g.100 mm, 60mm and 20 mm).

Results and Observations:

Record clearly any observations made, e.g. when flashover occurred.

Analysis of Results:

• Using the data from the logging equipment plot graphs of temperature versus time plus mass loss versus time,
• Make pertinent comments regarding the shape of the graphs,
• Calculate the average heat release rate for each experiment. (Note ?HC =26.08 MJ/kg for Methylated spirits) where Q= m? ?HC
• For one of the latter experiments calculate the ventilation limited fire size and compare it to the experimental result.

Conclusions:

Record any relevant conclusions you have made as a result of carrying out these experiments.

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