  A possible polar-ring debris disc, the dynamics of which can be described by
the outer hierarchical restricted three-body problem, has been detected in 99
Herculis. An empirical formula on the minimum radius beyond which test
particles in polar orbits can keep stable within ${10^7}$ binary periods is
provided through the numerical fitting, applying to the binary eccentricity
$e_{1} \in \left[ {0,0.8} \right)$ and the mass ratio of binary $ \lambda \in
\left[ {0.1,1} \right]$, where $ \lambda = m_0/m_1$ (${m_0}$ and ${m_1}$
represent the masses of the two binary stars). The polar planetary disc has the
lowerest statistical accretion efficiency and moderate impact frequency of
collisions among planetesimals (with a radius of 1-10km) compared to that in
the circumbinary coplanar disc and the standard disc around the single host
star. Colliding timescales in the circumbinary disk (both polar and coplanar
configuration) are longer than $10^7$ yr exceeding the dissipation timescales
of the gas disc. The stochastic simulations show that successive collisions
cannot make planetesimal grow up which may explain the formation of the debris
disc observed in 99 Herculis.
