Fire Load & Parametric Analysis | Bangladesh Buildings

🔥 Fire Load Density (q)

Fire load density represents the total combustible energy per unit floor area. In the Bangladesh context, high occupancy and textile-heavy interiors often require higher values than standard European codes.

q = Σ(m × H) / Area (MJ/m²)

Recommended Values for Bangladesh:

Building Type	Eurocode (MJ/m²)	Bangladesh Range (MJ/m²)
Residential	400 – 800	500 – 900
Office	300 – 600	400 – 700
Garments Factory	400 – 800	600 – 1200
Warehouse	800 – 2000	1000 – 3000

🪟 Opening Factor (O)

The opening factor accounts for ventilation. It determines how much oxygen enters the fire and how much heat escapes. High ventilation (large windows) leads to shorter, more intense fires.

O = (A_v × √h_eq) / A_t

A_v: Total area of vertical openings (m²)
h_eq: Weighted average height of openings (m)
A_t: Total internal surface area of the compartment (m²)

🧱 Thermal Inertia (b)

This describes the ability of the walls/ceiling to absorb heat. Materials like concrete have high thermal inertia, which helps keep gas temperatures lower by "soaking up" the energy.

b = √(ρ × c × λ)

Typical b-values (J/m²s^½K):

Concrete: 1160
Brickwork: 800
Gypsum Board: 600

⏱️ Time to Peak (t_max) & Duration (t)

The parameter t is the actual time elapsed since ignition. The fire reaches its maximum temperature at t_max, which is when the fuel is exhausted.

t_max = (0.13 × 10^-3 × q_t,d) / O

If t < t_max, the fire is in the Heating Phase. If t > t_max, the fire enters the Cooling Phase.

🧮 Calculation Process (EN 1991-1-2)

To find the gas temperature (Θ_g) at any time (t), the fictitious time factor (Γ) must be calculated first.

Γ = [ (O / b) / (0.04 / 1160) ]²

Temperature Equation

Θ_g = 20 + 1325 (1 - 0.324e^-0.2t* - 0.204e^-1.7t* - 0.472e^-19t*)

Where t* = t × Γ

Cooling Phase Rates

Heating Duration (t*_max)	Cooling Rate
t*_max ≤ 0.5h	625°C / hour
0.5h < t*_max < 2h	250°C / hour
t*_max ≥ 2h	125°C / hour

🎯 Key Recommendations

Adapt Eurocode values to the Bangladesh context by using "Medium" or "High" fire load scenarios.
For SAFIR modeling, ensure the thermal properties of local brickwork are correctly factored into the b value.
Always analyze the cooling phase, as structural failure often occurs during the contraction of members.