SCREAMER, SHORTY, ZIPPER & SCREAM-AIDS
Specifications and examples of use.

SCREAMER, SHORTY, ZIPPER & SCREAM AID Specifications:
Force needed for activation of a Screamer is >2kN. 
Standard Screamer and Shorty Screamer reduce peak forces on protection anchors by 3-4kN. 
Zipper Screamer reduces peak force on protection anchors by 6-7kN. 
Force needed for activation of a Scream-Aid is >1.5kN , they can absorb 1.5-2kN making them useful for only the most marginal placements.

UIAA recommends that protection devices hold the following loads.
Ice Screws-8kN
Friends-10kN(Mfg. range 7-14kN).
Pitons-12kN
Wire Nuts-12kn(Mfg. range 10-12kN).
RP-2kn(Mfg range 2-10kN).
Slings-22kN
Maximum impact force allowed on climbing Dynamic rope 6-9kn(Depending on size, 10.5mm=9kN).
Maximum impact force generate to running belay(Protection Anchors) is 15 kn. 1kN=225lbf.

Here are some useful examples where Screamers and Zippers are most effective.
1) Any high fall factor falls. FF=.5-2(Use ZIPPERS).
2) Moderate FF falls on marginal protection. FF=.25-1 (Use Screamers or Shorty).
3) Very low FF Falls on very marginal protection. FF=.1 and below -Use SCREAM-AIDS 

Example 1:
An Ice climber 175lb (80kg) has climbed 33ft(10m) above his belay. The climber places an Ice screw at 17ft(5m) above the belay. In the process of placing his second Ice Screw he slips and falls!! The climber placed a ZIPPER Screamer on his first piece of protection, which was 17ft(5m) above the belayer. The climber comes to rest next to his belayer, a little shaken but ok, the Ice Screw held the fall! 
This was a Fall Factor 1 fall thus generating a force of 11kN to the Ice Screw. A Fall Factor 1 is a very substantial fall. Ice screws have a rated strength in the 8kN range. With out the use of a ZIPPER Screamer in this situation the Ice Screw would have surely failed. This would have resulted in the climber falling an additional 33ft(10m) coming to rest well below the belayer. This type of fall could have severe and fatal consequences. The use of a ZIPPER Screamer in this case reduced the peak force on the first Ice Screw placement from 11kN to 5kN. 
In this same situation the use of a standard Screamer would have reduced the peak force on the Ice Screw placement from 11kN to 7kN. The use of a standard Screamer or a ZIPPER Screamer would have resulted in a similar outcome, as the Ice Screw should hold an 8kN peak load. In this situation a less than perfect Ice screw placement or a tied off Ice Screw would probably not hold unless the ZIPPER Screamer was applied. 


Example 2:
A Rock climber 175lb(80kg) has climbed 100ft(30m) above his belay. He placed six various protection anchors, SLCD's, wired nuts, and clipped a couple bolts. He is now at the 5.9 crux of this climb. The crack is very thin and our climber can only find a placement for a #3 RP(Rated at 5kN). Being a novas climber, but having a rack of all the cool gear he opts to place a shinny new SHORTY Screamer to this RP. The climber now tries for the crux move; at this point he is 8ft(2.5m) above the RP. He falls. Will the RP hold his fall??? 
The climber comes to rest 16.5ft(5m) below the crux move. This was a Fall Factor .33 fall thus generating a force of 7kN to the protection point with the #3RP. A #3 RP is has a rated strength of 5kN. A Fall Factor .33 is a very moderate fall, but with out the use of the Screamer the RP would surely have failed. This would have resulted in the climber falling an additional amount to his last piece of protection(If it held!). The use of a Screamer in this case reduced the peak force on the RP placement from 7kN to 4kN, resulting in the placement holding. In this same situation the use a ZIPPER Screamer could have reduced the peak force on the RP placement from 7kN to 2kN. The ZIPPER could have allowed a #0(strength 2.2kN) or #1 RP(strength 3.6kN) to have a high probability of holding. 


Example 3:
An Aid climber 175lb(80kg) has climbed 132ft(40m) above his belay. The climber placed 12 various protection anchors, SLD, wired nuts, clipping a few bolts and pounding a tied off pin. He is now at very thin spot in the crack and can only find a placement for a #1 RP(Rated at 3.6kN). The placement is solid but our experienced aid climber knows it can only hold about 800lbf(3.6kN). He opts to place a SHORTY Screamer to the #1 RP. The climber now works his way to the top step of his Etriers and places a #2 copperhead. At this point he is 6.5ft(2m) above the #1RP. He tests his #2 Copperhead and transfers his weight to the Copper Head, it pulls!!! Will the #1RP with the SHORTY Screamer attached fail or hold?
This fall generated a Fall Factor .1 thus generating a force of 1,000lbf(4.6kN) to the protection point with the #1 RP. Fall Factor .1 is a very light fall, but the #1RP is not very strong!! A #1 RP is has a rated strength of 3.6kN. With out the use of the Screamer the RP would probably have failed. This would have resulted in the climber falling an additional amount to his last piece of protection(If it held!). The use of a Screamer in this situation reduced the peak force on the #1 RP placement from 4.6kN to 2kN, resulting in the placement holding. The minimum force needed for activation of a Screamer is >2kn. In this situation the SHORTY Screamer could have theoretically reduced the peak force on the RP placement from 4.6kN to 1.5kN. The minimum activation needed for Screamer is >2kN therefore the Screamer in this situation only opened up about 80% or 8.5 of the 11" possible full exhaustion of the Screamer. 

Example 4:
An Aid climber 175lb(80kg) has climbed 132ft(40m) above his belay. The climber placed 12 various protection anchors, SLCD's, wired nuts, clipping a few bolts and pounding a tied off pin. He is now at very thin spot in the crack and can only find a placement for a #0 RP. Even though the placement seems good our experienced aid climber knows it can only hold about 600lbf(2.2kN). He opts to place a SCREAM-AID instead of a SHORTY Screamer to this #0 RP. The SCREAM-AID was chosen because the force needed for activation of a standard Screamer is >2 which is the above the breaking strength of the #0 RP. 
The climber now works his way to the second step of his Etriers and places a #0 copperhead. At this point he is 3.3ft(1m) above the #0RP. He tests his #0 Copperhead and transfers his weight to the Copper Head, it pulls!!! Will the #0 RP with the SCREAM-AID attached fail or hold?
This fall generated a Fall Factor .05 thus generating a force of 850lbf(3.8kN) to the protection point with the #0 RP. Fall Factor .05 is a very light fall, but the #0 RP is also a really weak placement. A #0 RP has a rated strength of 2.2kN. This would have resulted in the climber falling an additional amount to his last piece of protection(If it held!). The use of a SCREAM-AID in this case reduced the peak force on the RP placement from 3.8kN to 1.8kN, resulting in the placement holding. The minimum force needed for activation of a SCREAM-AID is >1.5kn.