  One of the proposed channels of binary black hole mergers involves dynamical
interactions of three black holes. In such scenarios, it is possible that all
three black holes merge in a so-called hierarchical merger chain, where two of
the black holes merge first and then their remnant subsequently merges with the
remaining single black hole. Depending on the dynamical environment, it is
possible that both mergers will appear within the observable time window. Here
we perform a search for such merger pairs in the public available LIGO and
Virgo data from the O1/O2 runs. Using a frequentist p-value assignment
statistics we do not find any significant merger pair candidates, the most
significant being GW170809-GW151012 pair. Assuming no observed candidates in
O3/O4, we derive upper limits on merger pairs to be $\sim11-110\ {\rm
year^{-1}Gpc^{-3}}$, corresponding to a rate that relative to the total merger
rate is $\sim 0.1-1.0$. From this we argue that both a detection and a
non-detection within the next few years can be used to put useful constraints
on some dynamical progenitor models.
