# Neqsim Firewater Deluge Design

> Educational fire-water and deluge coverage screening: area versus dedicated object demand, deluge nozzle-net sizing from both the flow and the spacing criterion, and fire-monitor screening with wind drift. USE WHEN: a task asks whether a process area has adequate fire-water coverage, how many deluge nozzles are needed, or whether monitors or passive fire protection can substitute for a fixed system.

- Skill: `equinor/neqsim-firewater-deluge-design` (Agent Skill, multi-file: 7 files)
- Install (CLI): `npx skillmds@latest add equinor/neqsim-firewater-deluge-design`
- Raw SKILL.md: https://api.skillmd.com/api/skills/equinor/neqsim-firewater-deluge-design/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Productivity
- Author: equinor (https://skillmd.com/u/equinor)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/equinor/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

```python
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

| Symptom | Cause | Fix |
| --- | --- | --- |
| Nozzle count too low, dry patches in the area | Sized on the flow criterion alone | Take the larger of the flow and coverage counts; check `governing_criterion` |
| Higher-K nozzles do not reduce the count | The layout is spacing-governed | Reduce the protected area or accept the grid; `K` cannot fix overlap |
| Demand far below expectation | Object surfaces entered as footprints | Use exposed wetted surface, e.g. `horizontal_vessel_surface_m2()` |
| Monitor concept looks adequate | Screened at zero wind | Re-run at the design wind speed and report `verdict` |
| Passive fire protection reduced because deluge was added | Substitution applied in the wrong direction | Keep passive protection; the rule runs one way only |

## 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