What You Need To Know About Importance Level 4 (IL4)

February 25, 2019 What You Need To Know About IL4 - Importance Level 4

What is IL4

IL4 (Importance Level 4) is the seismic restraints that are required for a tank that must be operational immediately after an earthquake or disastrous event for critical venues such as hospitals. A tank that meets these requirements and has undergone rigorous testing is the Fuelchief SuperVault. This includes the “California Shake test”. Here is a quick snippet of what is involved with the shake test.

In general, important structures define the significance of a building and its importance to society. Buildings that meet this category are hospitals, communications centres and those that provide occupation for many people; they are designed for a greater level of earthquake shaking than ordinary commercial structures.

The required level of seismic performance increases with each level of importance. With Level 5 being the highest. Clause A3 of the Building Code defines the significance of a building by its importance level (IL), which is related to the consequences of failure. The levels are listed below.

  • Level 1 (IL1): Structures presenting a low degree of hazard to life or property, such as walkways, outbuildings, fences and walls.
  • Level 2 (IL2): Normal structures and structures not covered by other categories, such as timber-framed houses, car parking buildings or office buildings.
  • Level 3 (IL3): Structures that may contain crowds, have contents of high value to the community or pose a risk to large numbers of people in close proximity, such as conference centres, stadiums and airport terminals.
  • Level 4 (IL4): Buildings that must be operational immediately after an earthquake or other disastrous event, such as emergency shelters and hospital operating theatres, triage centres and other critical post-disaster infrastructure.
  • Level 5 (IL5): Structures whose failure poses a catastrophic risk to a large area or a large number of people, such as dams, nuclear facilities or biological containment centres.

Who needs To Know About IL4

* Architects
* Building Designers
* Project Managers
* Builders
* Construction Industry
* Engineering Firms
* Local Government Bodies
* Property Developers
* Test Certifiers

The Importance of Meeting Seismic Regulations:

For Fuelchief, it is important that our SuperVault tanks that are used as back-up generators for critical environments (such as hospitals and communications facilities) are tested. Firstly, to ensure that emergency standby equipment remains undamaged in the event of an earthquake or power outage.

For Australia AS1170.4 ensures relevant actions to be taken in this space and refers to the New Australian Earthquake Loading Standard. Check out our resources at the end of this article for more information.

Most recently our Fuelchief SuperVault has been placed into a hospital in the Canterbury region, and to ensure it passed seismic testing, we enlisted the assistance of BVT to undergo the appropriate testing.

Below are images from the finite element analysis test:

Fuelchief element test seismic evaluation

Fuelchief seismic evaluation report




The Result

The SuperVault 22,000L can withstand and continue to function and service a building after a disastrous event.

To find out more about seismic levels and seismic resilience



Guide to Seismic Design – page 17 refers to IL4

Seismic Restraint of Engineering Services 


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