OK. It isn't a choice value by design. It needs to set and my "Zen-ability" is not quite there yet. I am using the "zen_draw_hidden_field" to set the value.
As in "'field' => zen_draw_hidden_field('opt_hazmat_handling', '1', $selected)". There is probably a better way to do this that sets the value to be fixed based on products choices on the basket.
Working on it.
TR