Neqsim Firewater Deluge Design

Fire-water and Deluge Coverage Design

Use this skill for public, educational fire-water coverage screening. It turns a protected area and an application rate into a water demand, a nozzle count and a grid pitch, and it tests the two alternatives that get proposed whenever a fixed deluge net is inconvenient: protecting the individual items instead of the area, and using fire monitors instead of a fixed system.

When to Use

• A verification finding says an area lacks active fire protection and the demand must be scoped.
• A modification adds hydrocarbon-bearing equipment to an area and the fire-water demand changes.
• Somebody proposes fire monitors, or passive fire protection, in place of deluge.
• You need a first nozzle count and grid pitch before a hydraulic network calculation.

Inputs

• protected_area_m2: plan area for general area coverage, m².
• area_rate_lpm_per_m2: application rate, (l/min)/m². Public minima are 10 for process areas and equipment surfaces and 20 for wellhead areas and riser balconies.
• objects: tuple of (tag, surface_area_m2, rate_lpm_per_m2) for dedicated protection.
• duration_min, foam_concentrate_percent, simultaneous_area_factor.
• Nozzle: nozzle_k_lpm_per_sqrt_bar, nozzle_min_pressure_barg, max_spacing_m, operating_pressure_barg, coverage_efficiency.
• Monitor: monitor_count, monitor_flow_lpm, wind_speed_m_s, fall_height_m, characteristic_dimension_m, line_of_sight_obstructed.

Outputs

• area_demand_lpm, object_demand_lpm, total_demand_lpm, total_demand_m3_per_h, water_volume_m3, foam_concentrate_m3, object_to_area_ratio.
• nozzle_count_from_flow, nozzle_count_from_coverage, nozzle_count, governing_criterion, grid_spacing_m, delivered_density_lpm_per_m2, pressure_adequate, density_met.
• nominal_density_lpm_per_m2, drift_displacement_m, wind_coverage_fraction, effective_density_lpm_per_m2, verdict.
• assumptions on every result.

Engineering Method

The Python class FireWaterCoverageModel uses open, published relations only.

• Demand is the application rate times the protected area, plus the sum of dedicated object surfaces times their rates, times a simultaneous-release factor.
• Nozzle discharge follows the orifice law $Q = K\sqrt{p}$ with $K$ in $(\mathrm{l/min})/\sqrt{\mathrm{bar}}$.
• The nozzle count is the larger of the flow criterion (total discharge must meet the density) and the coverage criterion (area divided by the square of the maximum permitted spacing). Sizing on flow alone is the classic error: it gives too few, too widely spaced nozzles that meet the average density but leave dry patches.
• Monitor droplets are drifted downwind by $\Delta x = h,u_{\mathrm{wind}}/v_t$, and the coverage loss is taken as linear in the drift over the characteristic target dimension.
• Shadowing is a flag, not a model: a monitor cannot wet a surface it cannot see.

Python Usage Pattern

from firewater_deluge_design import FireWaterCoverageModel

model = FireWaterCoverageModel()

demand = model.demand(
    protected_area_m2=420.0,
    area_rate_lpm_per_m2=10.0,
    objects=(("20-VA-001", model.horizontal_vessel_surface_m2(3.0, 9.0), 10.0),),
    duration_min=30.0,
)
print(demand.total_demand_m3_per_h, demand.object_to_area_ratio)

layout = model.deluge_layout(
    protected_area_m2=420.0,
    required_density_lpm_per_m2=10.0,
    nozzle_k_lpm_per_sqrt_bar=57.0,
    nozzle_min_pressure_barg=2.0,
    max_spacing_m=3.7,
    operating_pressure_barg=3.5,
)
print(layout.nozzle_count, layout.governing_criterion, layout.grid_spacing_m)

monitors = model.monitor_screening(
    target_area_m2=420.0,
    required_density_lpm_per_m2=10.0,
    monitor_count=2,
    monitor_flow_lpm=2400.0,
    wind_speed_m_s=12.0,
    fall_height_m=12.0,
)
print(monitors.effective_density_lpm_per_m2, monitors.verdict)

Validation Checklist

• The application rate comes from the governing project standard, not from the default: 10 (l/min)/m² for process areas, 20 for wellheads and riser balconies.
• Object surfaces are exposed wetted surfaces, not plan footprints.
• The nozzle count reports governing_criterion; a flow-governed count has been cross-checked against the maximum permitted spacing.
• pressure_adequate and density_met are both true, or the deficit is stated.
• The duration used for water_volume_m3 is traceable to the project basis.
• Monitor results are reported with the wind speed they assume.
• The result is presented as a screening input to a hydraulic network calculation.

Common Mistakes

Interpretation

• object_to_area_ratio well below 1 means selective protection of the hydrocarbon-bearing items is far cheaper in water than blanket coverage. Whether it is permitted is a requirement question, not a hydraulic one — the area-coverage requirement in NORSOK S-001 and ISO 13702 is written against the area.
• governing_criterion == "coverage" means the nozzle net is set by spray overlap, so a higher-K nozzle will not reduce the count.
• verdict == "marginal_wind_limited" means the monitor concept only works in still air.

Limitations

• Screening only. It performs no network hydraulics, no trajectory modelling and no CFD.
• It does not decide compliance. Application rates, durations and the acceptability of selective protection come from the governing project standard and the accepted deviations.
• It gives no credit for, and takes no credit from, passive fire protection. Fire water and passive fire protection are complementary barriers, and the regulatory rule runs one way: passive protection may not be reduced because active protection exists.

Related Skills

• neqsim-jet-fire-radiation-screening and neqsim-relief-load-screening — the fire side.
• neqsim-depressurization-screening — inventory removal, the primary barrier for a pressurised system.
• neqsim-safety-function-coverage-screening — whether the protective functions exist at all.

References

• NORSOK S-001, Technical Safety — fire-water application rates and area coverage.
• ISO 13702, Control and Mitigation of Fires and Explosions on Offshore Production Installations.
• NFPA 15, Standard for Water Spray Fixed Systems for Fire Protection — nozzle spacing and density.
• API RP 2030, Application of Fixed Water Spray Systems for Fire Protection in the Petroleum and Petrochemical Industries.
• NeqSim repository: https://github.com/equinor/neqsim