BESS Thermal Runaway Risk Assessment Calculator

Battery & Enclosure Parameters

Cell Chemistry

Battery Capacity (kWh)

Total installed energy capacity of the BESS

Enclosure Volume (m³)

Internal volume of the BESS enclosure(s)

Cell Spacing (mm)

Center-to-center spacing between cells12

Thermal Barrier Type

Detection System

Suppression Agent

Risk Level

Risk Score

Medium risk — consider upgrading detection system (VESDA recommended) and reviewing suppression agent quantities. Annual inspection per NFPA 855.

Heat Release Rate (HRR) vs Time

2800 Max Allowable HRR (kW)

40 Vent Gas Volume (m³)

18 Propagation Delay (min)

4.7 kg

120-minute HRR curve — exponential growth → peak → suppression decay — Vent ignition threshold

Cell-to-Cell Propagation Delay

18 minutes

■ <5 min ■ 5–15 min ■ 15–30 min ■ >30 min

Time for thermal runaway to spread from one cell to the next

Suppression System Sizing

4.7 kg (Minimum Agent Quantity)

1 × 50 kg cylinders

4.5% Design Concentration

— L/min

Battery Chemistry Data

200 Onset Temperature (°C)

60 HRR (per m²) (kW/m²)

0.04 Vent Gas Rate (m³/kWh)

8% H₂ (flammable gas)

Standards & References

Methodology & Equations

Max Allowable HRR: HRR_limit = k_vent × V_enclosure (kW)
Vent Gas Volume: V_vent = vent_rate × capacity_kWh (m³)
Suppression Agent: Mass = (C_v / 100) × V × ρ_agent × 1.15 (NFPA 2001)
Propagation Delay: t_prop = t_base × (spacing/12mm) × barrier_R_factor / HRR_factor
Risk Score = chemistry_risk + enclosure_factor + detection_factor + propagation_factor
LOW≤3 / MEDIUM 4-6 / HIGH 7-9 / CRITICAL≥10

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