the PACS spectrometer is , an infrared-luminous starburst galaxy with metallicity $\rm{Z=1/3~Z_{\odot}}$. Haro11 has the largest dataset obtained with PACS with observations of 7 FIR fine-structure lines: \[C [ii]{}\] 157, \[O [iii]{}\] 88, \[O [i]{}\] 63, \[O [i]{}\] 145, \[N [iii]{}\] 57, \[N [ii]{}\] 122, and \[N [ii]{}\] 205 $\mu$m. It has also been observed with the IRS spectrograph onboard [*Spitzer*]{}. Unresolved in the IR, Haro11 is an ideal candidate to conduct a study modeling an exhaustive set of gas tracers to retreive information about the structure of the multi-phase low metallicity ISM.

In this paper, we propose a systematic approach to model the multi-phase ISM of Haro11, focusing on the gas properties of the ionised and neutral ISM phases. We consider a set of 17 [*Herschel*]{} and [*Spitzer*]{} MIR and FIR ionic and atomic fine-structure cooling lines which trace a wide range of environmental conditions, spanning excitation potentials from 8 to 55 eV. With the spectral synthesis code Cloudy [@ferland-1998], we create a self-consistent model of the dominant ISM components from which these lines originate in order to understand the prevailing mechanisms and physical conditions. In Section \[sect:obs\], we present spectroscopic data from the [*Spitzer*]{} and [*Herschel*]{} observatories. Section 