Plastic Fire Suppression Tanks: A Safe Choice in 5 Points

Plastic fire suppression tanks: This is a common question when evaluating a water supply for fire suppression systems. Here, we clearly outline what can and cannot be done, and what precautions are needed to avoid problems such as implosion during startup of the pump-set.*

Plastic Fire Suppression Tanks: Frequently Asked Questions

The first two questions are direct:

• Can a plastic bathtub be placed outdoors?
• Is it possible to bury a plastic tub?

The answer, however, does not depend solely on the “tank” itself. It depends above all on what happens downstream of the tank—that is, on the pipes, fittings, and valves, and on their compatibility—especially in the above-ground sections.

The framework of the referenced standards (UNI 10779 / UNI 11443)

The guidelines cited above mention two key passages:

• UNI 10779:2014 – 6.2.1 (Pipes for above-ground installation): Metal pipes must always be used for above-ground sections.
• UNI 10779:2014 – 6.3 (Shut-off valves): Reference is made to compliance with UNI 11443 – 7.2.1, which stipulates that thermoplastic valves must be used only in systems where the pipes are manufactured using the same technology.

The practical point is that it’s not enough to simply “buy the tank”: the choice of tank dictates the choice of materials for the connected system.

Why outdoor installation limits the choice to “metal or concrete only”

The combination of the above indications leads to a clear operational conclusion.

If only metal pipes can be used above ground, then also:

• fittings on those pipes;
• valves on those pipes;

They must be made of metal, because they are part of the same system and follow the same material compatibility guidelines as those specified for the valves.

This leads to the crucial point: since the pipes leading out of the storage tanks are above ground (i.e., not buried), they must be made of metal and must be connected to:

• downstream to metal pipes;
• upstream to storage tanks, which, accordingly, may only be made of metal or concrete.

In other words: All outdoor fire protection storage tanks must be made of metal or concrete.

What about underground installation? When is plastic allowed?

On the other hand, it is explicitly stated that plastic fire protection water tanks may only be used for underground installation.

This distinction between “above ground” and “underground” is not presented as a construction detail, but as a practical consequence of the constraints (mentioned) regarding:

• materials used for above-ground piping (metal);
• Compatibility between thermoplastic valves and pipes manufactured using the same technology.

So, if the goal is to use plastic, the way forward is clear: an underground solution.

Valves and Fittings: The Issue of Material Compatibility

The technical issue, as it stands, is the compatibility of technology and materials.

Specifically, it is stated that:

• Thermoplastic valves should be used only if the pipes are also manufactured using the same technology;
• It is not possible to install thermoplastic valves on metal pipes, whether they are buried or not.

This point is important because it explains the reasoning behind many “necessary” choices on-site: if part of the system requires the use of metal (such as in above-ground sections), this automatically limits the options for valves and fittings as well.

Implosion: Can It Happen? And What Precautions Should Be Taken?

The last question is very specific: if the pump unit is started up, could the tank collapse in on itself?

For underground plastic tanks, it is noted that there is a possibility of implosion. For this reason, it is stated that all necessary precautions must be taken to prevent this from happening.

The precautions mentioned (without going into specific figures) include:

• properly sizedvent and air intake pipes;
• ribs, and other structural features, where applicable.

The key point to keep in mind is that the underground plastic system should not be treated as “plug-and-play”: a careful assessment is needed of the conditions that could lead to depressurization or imbalances during startup.

A Quick Checklist Before Making a Decision

Before deciding between an outdoor or underground pool, it may be helpful to use a basic checklist that aligns with the points mentioned above:

1. Does the installation include any above-ground sections? If so, keep in mind that the pipes must be made of metal.
2. Are thermoplastic valves included? Verify that they are used in systems with pipes made of the same material (and not on metal pipes).
3. Are the outlet fittings on the tank external? If so, they must be made of metal, and the material must be consistent across the tank and the connections.
4. If you are considering an underground plastic tank, have the necessary precautions (properly sized vent/air intake, ribs, etc.) been taken to reduce the risk of implosion?

Conclusion

In summary: For outdoor use, fire protection storage tanks should be made only of metal or concrete, while plastic fire protection tanks are recommended only for underground installation. If you choose an underground plastic tank, you must also consider the possibility of implosion and take the necessary precautions.