Answer;
400 pounds 
400 pounds is the number of pounds that a sand bag must weigh to test if a safety net can absorb the proper amount of force.
Step-by-step explanation;
The drop test consists of a 400 lb. sandbag dropped from the highest height from which a potential fall might occur, and from no fewer than 42 inches above that level.
Safety nets must be drop-tested on the job site at the following times: 
-  After installation and prior to first use 
- If the net is relocated 
- After a major repair 
- After six months, if the net is left in place