@Mod(...)
public class mod{
    @EventHandler
    public void load(FMLIntitializationEvent event){
        MinecraftForge.event_bus.register(new OxygenAtmosphere);
    }
}
import micdoodle8.mods.galacticraft.api.event.oxygen.GCCoreOxygenSuffocationEvent.Pre;
public class OxygenAtmosphere{
    @ForgeSubscribe
    public void cancelDamage(Pre event){
        if(provider.getDimensionID == OxygenAtmospherePlanetID)
            event.setCancelled(true);
    }
}