  We examine the properties of a sample of 35 nearby passive spiral galaxies in
order to determine their dominant quenching mechanism(s). All five low mass
($\textrm{M}_{\star} < 1 \times 10^{10} \textrm{M}_{\odot}$) passive spiral
galaxies are located in the rich Virgo cluster. This is in contrast to low mass
spiral galaxies with star formation, which inhabit a range of environments. We
postulate that cluster-scale gas stripping and heating mechanisms operating
only in rich clusters are required to quench low mass passive spirals, and
ram-pressure stripping and strangulation are obvious candidates. For higher
mass passive spirals, while trends are present, the story is less clear. The
passive spiral bar fraction is high: 74$\pm$15%, compared with 36$\pm$5% for a
mass, redshift, and T-type matched comparison sample of star forming spiral
galaxies. The high mass passive spirals occur mostly, but not exclusively, in
groups, and can be central or satellite galaxies. The passive spiral group
fraction of 74$\pm$15% is similar to that of the comparison sample of star
forming galaxies at 61$\pm$7%. We find evidence for both quenching via internal
structure and environment in our passive spiral sample, though some galaxies
have evidence of neither. From this, we conclude no one mechanism is
responsible for quenching star formation in passive spiral galaxies - rather, a
mixture of mechanisms are required to produce the passive spiral distribution
we see today.
