Forms :: Wait Event During Execution Simple Select Statement

Yesterday i got wait event when executed simple select from table.This select was like:

SELECT emp_number from employer where subs_id = 111

I got one row, select is very fast.In our Core Bank System we have package with function which returns such information. I tested this select on test DB, and nothing wrong. But when I executed such select and package on Production DB, DB Admin saw that 88 sessions waits when my session release the resource. But what can happen, it was simple select? I used PL/SQL developer to get information from table:

1) SELECT emp_number from employer where subs_id = 111 then
2) Package with this function

Another users used Oracle Forms screen to execute package. How simple select statement could stop all DB?

BANNER
1Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi
2PL/SQL Release 10.2.0.5.0 - Production
3CORE 10.2.0.5.0 Production
4TNS for 64-bit Windows: Version 10.2.0.5.0 - Production
5NLSRTL Version 10.2.0.5.0 - Production
[code]...

Forgot to say that after succeful execution on Prod DB I disconnected, and in EM my session was INACTIVE.