IPVMU Certified | 06/14/16 10:01pm
1. The omission of a mullion may have as much to do with what is transported through the door than just people flow.
Think a load of cargo on a cart that is 60" wide. If this opening is attached to a group meeting area, it might be an important access point for equipment.
This is an example of a mullion for those who may not be familiar:
An alternative to fixed mullions are 'removable mullions':
Mullions impact door usability, but they also tend to increase/simplify door security. Having a fixed positive latching point in a mullion beats vertical rods any day.
In general flow calculations are linear, and I'm not sure a mullion has a negative impact on egress volumes. However, I'll confirm that with some contacts and report back here.
2. Cost is the biggest factor. One double leaf door is less expensive to fabricate/install/maintain than two single doors immediately adjacent to each other. Getting two butted frames to align properly sounds really maddening to me.
3. Vertical rods are a very maintenance-intensive component. Show me a double door with rods, and I will show you a door that likely does not latch properly. There are 'security minded' hardware consultants that refuse to spec vertical rods on perimeter doors because of this.
UND1- Just my opinion; I would not argue at all with most of the comments here about Verticals. They are expensive, harder to install and when they start to fail, they are a nightmare. I will add to that by saying the power supply for Von Duprin is 12 AMPS!! That is a ton of power required in facilities that may or may not have that much power available. When we are talking about standard office complexes, that is an entire circuit dedicated to one power supply for one door.
Here is what else I will say. We have installed hundreds of them in a number of states. I have not had one AHJ reject them, ever. The clear advantage is that you have to use your credentials to get in, and they offer mechanical egress. Just push on the bars from the inside and exit. They meet the fire code everywhere we go. We get push-back from some AHJ's on other means of egress from time to time, but never a word about vertical rods.
Yes we do use Von Duprin and no others, but that is more about inventory than anything else. They are very expensive. We don't have to keep a variety of every expensive parts on trucks. Just one.