EN 12845 design parameters for class HHP3 — High Hazard Process 3: design density 12.50 mm/min, area of operation 260 m², water supply duration 90 minutes.
Which areas fall into this class?
The process class requiring the highest density; production with substantial flammable liquid and plastics content.
Design parameters
| Parameter | Value |
|---|---|
| Design density | 12.50 mm/min |
| Area of operation (wet / alternate) | 260 m² |
| Water supply duration | 90 minutes |
| Theoretical minimum sprinkler flow | 3250 L/min |
| Theoretical minimum water volume | 292.5 m³ |
The theoretical minimum values come only from density × area. The real design flow is higher because of hydraulic imbalance and the minimum sprinkler pressure, and hose reel and hydrant flows are added on top.
Required pressure by K-factor
For a sprinkler covering 12 m², the required flow is 150.0 L/min. The pressure needed at different K-factors:
| K-factor | Required flow (L/min) | Required pressure (bar) |
|---|---|---|
| K57 | 150.0 | 6.93 |
| K80 | 150.0 | 3.52 |
| K115 | 150.0 | 1.70 |
| K160 | 150.0 | 0.88 |
Where the result falls below the minimum sprinkler pressure the standard requires, the minimum is used and the flow recalculated.
Dry and pre-action systems
Because water arrives late in dry and pre-action systems, the area of operation is increased. The increase depends on the standard chosen; NFPA 13 requires the design area to be increased by 30% for dry and pre-action systems.
Classification is a decision; the table is a consequence. Whether an area falls into class HHP3 — High Hazard Process 3 is determined by assessing its actual activity, stored materials and fire load, and defended with a written justification in the design report. If the classification is wrong, every number here is invalid.
Checklist
- Has the area's activity and stored material been defined in writing?
- Have sections of the same building in different classes been calculated separately?
- Where there is storage, have the storage rules been applied as well?
- Have hose reel and hydrant flows been added to the total demand?
- Have the water supply duration and volume been verified?
- Is there any planned operational change that could alter the class?
Frequently Asked Questions
What is the design density for class HHP3?
Under EN 12845, 12.50 mm/min over a 260 m² area of operation, with a 90 minute water supply duration.
What minimum water volume does HHP3 need?
A theoretical minimum of 292.5 m³ (density × area × duration). The real volume is higher because of hydraulic imbalance, minimum sprinkler pressure and hose reel and hydrant flows.
Do these values change on a dry system?
The area of operation is increased. NFPA 13 requires the design area to be increased by 30% for dry and pre-action systems.
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Download MEP Calc on the App StoreBS EN 12845:2015+A1:2019 · NFPA 13 (2025). Table values are for information; the binding text is the current edition of the standard, and separate rules apply to storage.