We present preliminary results of a detailed analysis of the $z=3.55$ Lyman limit system observed in the optical spectrum of Q2000-330. We have fitted Voigt profiles to the system to determine the column densities and Doppler parameters of its many components. For its major components we have also determined the ionisation fraction of the gas and obtained crude estimates of metallicities. We find order of magnitude variations in ionisation fraction and metallicity in components separated by as little as 150 km s$^{-1}$ in velocity space. This work is presented as an example of a campaign we have begun to collect such information on a sample of $\sim 100$ such systems in an effort to accurately characterise this enigmatic and important class of quasar absorption line systems.