Oxygen Filters

Description
Filters are a "consumable" item that can be used in a pinch to save your life by providing you with oxygen. They are similar to Power Cells in the way that they work.

Crafting
Filters must be researched before you can craft them. Once available, they are crafted from only 1 compound.

Usage
Filters is actually a set of 4 small tanks which contains 20 seconds of oxygen each (total 80 seconds, when not running).

A filter only activates if you don't have access to any other oxygen supply, such as tethers or mined oxygen.

When one of the filter parts starts to be used, it disappear and during the next 20 seconds, you don't consume oxygen from your other tanks.

TODO : check behavior when you craft filters when you have an empty main and secondary tanks. Do they fill up both (they should fill the main tank then a little of the secondary one) ?

[ja:Filter ja:Filter]