blast design using Time history analysis

Dear All

I have few questions that confusing  .

1. The Pressure Symbol of Time History Load( left-right headed arrow ), what does it mean   and how to define the pressure downward or upward ( inward or outward )? 

2. Is that correct if  I define the pressure with ( minus/ plus ) value according my requirement ?

3.For  Blast load case , I understand that SELFWEIGTH X1,SELFWEIGTH Y1 and SELFWEIGTH Z1 are used to define the mass of building to behave the dynamic analysis.

But If I use additional load on floor / beam to represent my R.C wall ( e.g PR Gy -10 ) , do I need to add this load under the Blast Load Case title also ?

Kindly advice me to make sure these issues.

I am looking forwards your advice in urgently .