Aims: To assess the composition of the Natural Gas (NG) supplied for domestic consumption through the distribution network to correlate the physical properties linked to it were to be determined in order to investigate their fluctuations.

Study Design:  The samples were analyzed in accordance with the method described in the ISO 6974‑4 standard, “Natural Gas. Determination of Composition with Defined Uncertainty by Gas Chromatography”.

Place and Duration of Study: Center of Technology Research, Fuels Laboratory, between January and December 2016.

Methodology: Over the course of the year, a total of eighty-four samples of natural gas for domestic use were analyzed.  These were collected at a rate of one per month in seven cities in the geographical zone under study (Galicia_Spain), in which the number of users is significant.

Results and Conclusion: The protocols for technical management of the Gas System have a section on quality specifications for Natural Gas at entry points to the system.  This sets limits for only three of the physical properties of natural gas: Wobbe index, superior calorific value and relative density.

The figures obtained for Wobbe index, superior calorific value and relative density from the eighty-four samples studied showed that the quality of the Natural Gas distributed remained steadily within the acceptable limits throughout the whole year. The values for standard deviations bore witness to the fact that any variations did not significantly alter the quality of the Natural Gas supplied.

The concentrations of the odorant, THT, were always above the recommended value of 18.0 mg/Nm3, the fluctuations noted over the course of the year were such as to make it possible to see them as excessive. In some instances, a high concentration of odorant may lead users to erroneous impressions, so that they come to think that there are leaks from the gas-pipes or even that the gas is not burning properly.

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