  Strongly conflict-avoiding codes (SCACs) are employed in a slot-asynchronous
multiple-access collision channel without feedback to guarantee that each
active user can send at least one packet successfully in the worst case within
a fixed period of time. Assume all users are assigned distinct codewords, the
number of codewords in an SCAC is equal to the number of potential users that
can be supported. SCACs have different combinatorial structure compared with
conflict-avoiding codes (CACs) due to additional collisions incurred by
partially overlapped transmissions. In this paper, we establish upper bounds on
the size of SCACs of even length and weight three. Furthermore, it is shown
that some optimal CACs can be used to construct optimal SCACs of weight three.
