The provision logic: cumulative thresholds
The SI 4 provision table works by accumulation: every building starts from a common basic provision and keeps adding systems as it crosses thresholds of built area, evacuation height or occupancy, with particular requirements per use. This mechanism explains the package's most characteristic budget phenomenon: cost does not grow continuously with building size, it grows in steps. A few more square metres, or one more floor, can trigger an entire system.
The systems, from the most common to the most demanding
Portable extinguishers. The universal provision. The general rule is that no point of an escape route may be more than 15 metres from an extinguisher of the minimum required rating, with additional provision in special risk rooms. A minor item in amount, a mandatory presence in every budget.
Equipped fire hose reels. BIE (bocas de incendio equipadas, equipped fire hose reels) appear when area thresholds depending on use are exceeded, generally in non-residential uses from medium areas upwards, and they drag their own supply network with them: pipework, and in many cases a pressure group and tank when the public network does not guarantee the flow and pressure conditions. That supply is the expensive part and the most forgotten in early estimates.
Detection and alarm. Automatic detection and the alarm system are required by use and area, with implementations ranging from call points and sounders to full detection throughout the building in the larger uses and sizes. Today's market combines conventional systems, which identify the zone in alarm, and addressable analogue systems, which identify the specific device; the choice weighs on price and maintenance, and in medium and large buildings the balance tips towards addressable for its operation.
Exterior hydrants. Required according to area and use, they depend heavily on the existing urbanisation: where the public network already offers hydrants in the due conditions, the item disappears from the building's budget; where it does not, it appears with its civil works.
Dry riser. The firefighter support installation, generally required from 24 metres of evacuation height: an empty pipe with inlets at the façade and outlets per floor that fire services pressurise from their vehicle. Moderate cost, frequent omission in change-of-use projects on tall buildings.
Automatic sprinklers. The automatic extinguishing installation, the most expensive of the repertoire, is required in the larger uses and sizes, large retail for example, and in certain singular rooms. Its presence also has crossed effects on the rest of the document: section SI 1 allows compartments to be enlarged where automatic extinguishing exists, which turns sprinklers into a design variable and not just an obligation. The choice of the doors and elements completing the compartmentation is developed in the article on fire doors.
The water supply: the submerged item
Experience analysing budgets teaches that the package's typical economic error is not in the visible equipment but in its feed. Hose reels, private hydrants and sprinklers need a supply with guaranteed flow, pressure and autonomy, and where the urban network does not guarantee them, the design must incorporate a reserve tank and a fire pressure group, with its plant room, which in turn is a special risk room with its own requirements. This chain, equipment, network, supply, room, is what must be budgeted in full; cutting it at the first link produces the package's classic deviations.
Budget reading of the package
| System | Relative cost order | Omission risk |
|---|---|---|
| Extinguishers and signage | Low | Low |
| Detection and alarm | Medium | Medium, in the real required extent |
| Hose reels with their network | Medium | High, in the supply |
| Dry riser | Low to medium | High in existing tall buildings |
| Hydrants | Variable | High, depends on the urbanisation |
| Sprinklers | High | Low when required, high in their design effects |
As an indicative order of magnitude, the fire protection package as a whole moves in ordinary residential and commercial buildings between 1 and 3 % of the PEM (presupuesto de ejecución material, the direct construction cost), with much higher values when sprinklers or complete supplies come in. The traceability of these items within the general method is explained in the article on the cost of CTE compliance.
Frequent errors
The first is budgeting equipment without supply, the submerged error already described. The pressure group and the tank are the item discovered late.
The second is reading the provision table once and for a single use: in mixed buildings, each use zone contributes its requirements, and the resulting provision is the coherent sum of all of them. Each zone is analysed with its own use and its own area.
The third is ignoring maintenance when comparing solutions: the RIPCI imposes maintenance programmes with defined periodicities, and the operating difference between systems can exceed the investment difference within a few years. The comparison is made on life cycle cost rather than on capital cost.
The fourth is forgetting that the protection installation is also civil works: plinths, rooms, sealed penetrations through compartments, preferential electrical feeds. Coordination with the compartmentation of the article on fire compartments prevents the fire protection installation itself from perforating the compartmentation it must protect.
Note: the thresholds and values cited are general references; the provision required in each case is that of the table of the consolidated DB-SI in force and the technical conditions those of the RIPCI, both in their official texts.