A failed zero test may be due to insufficient purging and consequently, contamination from a
previous sample. To eliminate this as a possible cause, purging should be continued and the
test repeated. If the issue remains unresolved the noise level of the analyser should be
checked. This may be done by visual examination of baseline noise differences between the
current and previous zero gas spectra. If an increase in the noise is found the manufacturer
should be consulted. If an increase in noise is not found the integrity of the zero gas and
sampling system should be checked.