Basic Documentation
Table Of Contents
- About this Application Guide
- Chapter 1–Introduction
- Chapter 2–Goals of the Laboratory Environment
- Chapter 3–Unique Ventilation Needs of a Laboratory Facility
- Chapter 4–Ventilation Systems Classification
- Chapter 5–Laboratory Facility Exhaust Systems
- Chapter 6–Laboratory Containment Units - Ventilation
- Chapter 7–Room Ventilation, Makeup Air, and Pressurization Control Systems
- Chapter 8–Laboratory Temperature and Humidity Control Systems
- Chapter 9–Laboratory Emergencies - Ventilation System Response
- Chapter 10–Laboratory Ventilation System - Validation
- Chapter 11–Laboratory Ventilation System - Commissioning
- Glossary
- Index
Chapter 5–Laboratory Facility Exhaust Systems
Laboratory Exhaust Systems - General
Requirements
Exhaust System Materials
Individual exhaust systems for chemical fume hoods pose the harshest environment
for exhaust system materials since the fumes from any one fume hood can be very
corrosive and highly concentrated. On the other hand, centralized exhaust systems
typically benefit from a much higher dilution factor and are therefore less likely to be
so severely attacked.
To prevent high concentrations of fumes in a fume hood or in the exhaust system, all
chemical fume hoods (particularly VAV hoods) should always have a minimum airflow
through them when even when the sash is fully closed. The minimum recommended
airflow rate is approximately 20% of the maximum fume hood exhaust airflow.
There is no universally agreed upon material that is best for all exhaust systems.
Each facility must be appraised for its particular situation and needs. For specific
chemical compounds, consult a handbook which provides a thorough listing of
chemical resistance properties for specific materials. Following is a description of
those materials most applicable for laboratory exhaust systems. It’s intended to be a
guide regarding materials generally applicable to chemical fume exhaust systems.
Stainless Steel
Type 316 is the most resistant stainless steel alloy and is used for the majority of
laboratory exhaust systems. However, it is not suitable for applications with
substantial amounts of bromine, fluorine, or iodine and their acids. It is also not
suitable for heavy use of sulfuric acid as well as ferric, stannic and mercuric
chlorides.
Galvanized Steel
Although this material has limited resistance to many compounds and is not
recommended for general use, it may be considered where chemical fumes are not
highly concentrated and when fumes will be generated only a small portion of the
time. It is best used with centralized exhaust systems in secondary schools, smaller
colleges and in medical facilities where large amounts of highly corrosive fumes
would not be produced and where the actual usage time of the fume hoods is limited.
PVC
PVS is being used more often since it has excellent resistance to most acids.
However, is not recommended for acetate and benzene compounds or strong
solvents. It should not be used when exhaust air temperatures will exceed 50°C.
Since PVC will give off hydrogen chloride gas in a fire, local codes usually require
PVC ducts to be installed within a fire rated chase when inside of the building.
36 Siemens Building Technologies, Inc.