  We study close approaches in hierarchical triple systems with comparable
masses using full N-body simulations, motivated by a recent model for type Ia
supernovae involving direct collisions of white dwarfs (WDs). For stable
hierarchical systems where the inner binary components have equal masses, we
show that the ability of the inner binary to achieve very close approaches,
where the separation between the components of the inner binary reaches values
which are orders of magnitude smaller than the semi-major axis, can be
analytically predicted from initial conditions. The rate of close approaches is
found to be roughly linear with the mass of the tertiary. The rate increases in
systems with unequal inner binaries by a marginal factor of $\lesssim 2$ for
mass ratios ${0.5<m_1/m_2<1}$ relevant for the inner white-dwarf binaries. For
an average tertiary mass of $\sim 0.3 M_{\odot}$ which is representative of
typical M-dwarfs, the chance for clean collisions is $\sim 1$% setting
challenging constraints on the collisional model for type Ia's.
