how to convert a time interval to seconds?

Hi,

I searched how to convert a time interval to seconds but failed to find
an example.

I want to convert the following wait_time column into seconds. How can I
do that? The datatype for the wait_time is time without timezone.

 job_number | task_number |   submission_time   | wait_time
------------+-------------+---------------------+-----------
         56 |           0 | 2006-04-13 08:47:53 | 00:01:28
         55 |           0 | 2006-04-13 08:47:51 | 00:01:21
         58 |           0 | 2006-04-13 08:47:54 | 00:01:28
         60 |           0 | 2006-04-13 08:47:55 | 00:01:27

Thanks,

- Chansup