Industrial liquid storage must be robust and safe. While all liquid storage tanks in all settings must be dependable, industrial tanks must be highly resilient, given the nature of what they contain. High design and manufacturing levels are one piece of the equation when seeking trustworthy liquid storage. Suitable materials and seismic restraints are the other pieces.
Why industrial storage sets a higher bar
Many industrial tanks store stormwater and wastewater, but just as many are used for chemical storage or for providing water for essential activities, such as firefighting. The consequences of failure scale with the contents. A tank that shifts off its base does not simply spill water: it can release something hazardous, or remove the supply a site depends on at the exact moment that supply matters most. That is why an industrial tank is judged on more than its capacity. Design, manufacturing quality, material choice and the way the tank is held down all contribute, and a weakness in any one of them undoes the others. Water held for fire service connections is a clear example of storage that has to still be there afterwards.
New Zealand's seismic record
In New Zealand, we must consider our seismic history when discussing industrial liquid storage. GeoNet calculates that New Zealand should experience 50 magnitude 5 earthquakes and two magnitude 6 earthquakes each year, four magnitude 7 earthquakes per decade, and a magnitude 8+ earthquake every century. Those are not once-in-a-lifetime numbers. They describe a country where a tank installed today can reasonably be expected to be shaken during its working life, and shaken more than once. We are an earthquake-prone country, and that makes liquid storage a more challenging proposition here than it is in most places.
Why poly handles a quake better than concrete
Poly storage tanks are universally accepted as being best suited to handle earthquakes. The flexible nature of poly tanks makes them far more ductile than any other material, including concrete and fibreglass. In other words, poly storage tanks can better absorb the stresses and forces of a seismic event rather than resist them until something gives. Rigidity is not the same as strength. A material that cannot flex has to take the energy of the shake through its structure, and brittle materials fail suddenly when that limit is reached. Ductility gives the tank a way to survive the movement instead of fighting it. This sits at the heart of the concrete versus plastic comparison.
What happened at Ward after Kaikoura
One example is the 2016 Kaikoura earthquake, which badly damaged the concrete tanks that made up the community water scheme in the Marlborough settlement of Ward. To safeguard water storage after the quake, the concrete tanks were replaced with eight 30,000 litre Promax poly tanks, with this material chosen for its ability to better withstand considerable seismic activity. It is a useful case precisely because the decision was made after the event, by people who had just watched the alternative fail. Nobody rebuilding a community water supply from that position is choosing on theory alone.
What a seismic restraint actually does
Seismic restraints add another layer of safety by acting as a set of anchors for large industrial storage tanks. A series of restraints around the tank's base are bolted into a concrete pad to hold the tank in place and prevent movement during an earthquake or other events, including cyclones and floods. The logic is straightforward. A poly tank set solid and immovable at the base, and with flexibility and durability throughout the rest of the structure, appeals as the safest and most robust option for liquid storage. The base stays put and the body absorbs what the base transmits, which only works if both halves are specified together, along with the right fittings for the tank.
Restraints on residential tanks
This is ideal for industrial tanks, with residential tanks also capable of being anchored using restraints and braces on a smaller scale. For example, the Promax Slimline Seismic Bracing Set for 3,000 and 5,000 litre tanks is designed and built to meet virtually all seismic loading requirements within New Zealand. Meanwhile, all Promax Slimline tanks feature in-built seismic restraint systems for added stability in residential applications. A domestic tank is smaller, but it usually sits hard against the house and beside the drive, which is reason enough to want it held exactly where it was put.
Where Promax restraints are rated for use
Promax Seismic Restraints for industrial tanks perform a vital function and are rated highly enough to be used in buildings with Importance Levels (IL) 1, 2, and 3. Importance Levels are determined according to a building's function, occupancy, and consequences of failure during a seismic event. Every component that contributes to a building's ongoing operation, even after a significant seismic or weather event, is vital, and in a higher Importance Level building that includes the tank and the hardware holding it down. This is what puts restraints into the specification rather than onto the accessories list, a point worth reading alongside our guide to storage solutions in seismic zones.
How the building code defines Importance Levels
The building code defines them as follows:
- IL1: Buildings posing low risk to human life or the environment, or a low economic cost, should the building fail. These are typically small non-habitable buildings, such as sheds and barns, that are not normally occupied, though they may have occupants from time to time.
- IL2: Buildings posing normal risk to human life or the environment, or a normal economic cost, should the building fail. These are typical residential, commercial, and industrial buildings.
- IL3: Buildings of a higher level of societal benefit or importance, or with higher levels of risk-significant factors to building occupants. These buildings have increased performance requirements because they may house large numbers of people, vulnerable populations, or occupants with other risk factors, or fulfil a role of increased importance to the local community or to society in general.
No region is exempt
Major earthquakes still occur in regions with a history of lower seismic activity, and the events in Christchurch acted as a stark reminder of this. Declining to restrain a tank because the local record looks quiet is a bet against that reminder. Throughout New Zealand, there is no room for complacency when it comes to securing liquid storage tanks, and when it comes to industrial storage, there is no margin of error anyway. In this light, seismic restraints are not just a sensible way to enhance safety but also an essential one. Talk to Promax about restraints across the industrial range.