  Massive stars are known to have a high multiplicity, with examples of higher
order multiples among the nearest and best studied objects. In this paper we
study hierarchical multiple systems (an inner binary as a component of a wider
binary) of massive stars in a clustered environment, in which a system with a
size of 100--1000 au will undergo many close encounters during the short
lifetime of a massive star. Using two types of N-body experiment we determine
the post-formation collision probabilities of these massive hierarchies. We
find that, depending on the specifics of the environment, the hierarchy, and
the amount of time that is allowed to pass, tens of percent of hierarchies will
experience a collision, typically between the two stars of the inner binary. In
addition to collisions, clusters hosting a hierarchical massive system produce
high velocity runaways at an enhanced rate. The primordial multiplicity
specifics of massive stars appear to play a key role in the generation of these
relatively small number events in cluster simulations, complicating their use
as diagnostics of a cluster's history.
