Designing laboratory ventilation systems

Proper ventilation in labs is required to promote and maintain safety and protection to life and property.

01/21/2014


Learning objectives

  1. Understand the codes and standards that guide laboratory ventilation design.
  2. Learn how to design laboratory ventilation systems to meet system requirements.
  3. Understand key equipment functions. 

This article has been peer-reviewed.Proper ventilation of laboratory settings is required to promote and maintain laboratory safety and protection to life and property. Items such as fume containment, worker safety, proper cleanliness through pressure relationships, filtration, air changes per hour (ACH), point of fume capture, temperature, and relative humidity requirements are elements necessary to design the ventilation system depending on the laboratory type. Codes identify ventilation measures to provide minimum requirements for the protection of life and property through prevention and control of fumes and containment of hazardous fumes and contaminants for worker safety.

There are four general types of laboratories noted in the ASHRAE HandbookHVAC Applications:

  1. Biological: Contains biologically active materials and includes areas such as biochemistry, cell biology, immunology, pharmacology, microbiology, and related fields. Clinical laboratories fall into this category.
  2. Chemical laboratories that support both organic and inorganic synthesis and analytical functions.
  3. Animal labs that include areas for the observation, manipulation, and pharmacological observation of laboratory animals and also include animal holding rooms.
  4. Physical laboratories are spaces associated with physics and include lasers, optics, high- and low-temperature materials, and analytical instruments. 

Biological laboratories commonly have chemical fume hoods and Class I and Class II bio-safety cabinets. Chemical labs generally have a number of fume hoods.

This article will provide information on hood types and ventilation criteria primarily on the first three types of labs, with discussion on contaminant containment, airflow practices, comfort conditioning, and the codes that govern the lab ventilation systems.

Applicable codes and standards

The 2011 edition of NFPA 45: Standard on Fire Protection for Laboratories Using Chemicals applies to laboratory buildings, units, and work areas in which defined chemicals are handled or stored. Chapter 8, Laboratory Ventilating System and Hood Requirements, defines criteria and considerations for exhaust air and supply air systems including requirements for fume hood exhaust.

ANSI/AIHA Z9.5-2012 - Laboratory Ventilation describes required and recommended practices for the design and operation of lab ventilation systems for control of exposure to airborne contaminants. It does not apply to animal facilities, laminar flow hoods, or bio-safety cabinets. Chapter 5 of this standard discusses laboratory ventilation system designs.

In the 2011 ASHRAE Handbook—HVAC Applications, Chapter 16 provides detailed descriptions of laboratory airflow, fume hood types, hazard assessments, exhaust systems, and applications to various lab types.

NFPA 99: Health Care Facilities Code, 2012 edition, has deleted the previously included chapter pertaining to laboratories and has added a new Chapter 4, which establishes four “Categories of Risk.” Also included is Chapter 9 outlining HVAC requirements for health care facilities. References are made in this chapter to NFPA 45 and ASHRAE Standards 90.1, 90A, and 170. This code will pertain primarily to clinical labs and related spaces whether within a hospital or separate building.

The 2010 edition of FGI Guidelines for Design and Construction of Healthcare Facilities incorporates ASHRAE 170-2008 (with addenda): Ventilation of Health Care Facilities, which has specific requirements for laboratory ventilation including pressure relationships, air change rates, and temperature and relative humidity requirements.  

ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality identifies minimum ventilation rates in the breathing zone (Table 6-1) and minimum exhaust rates (Table 6-4) for laboratories and other spaces. (Standard 62.1-2013 was released in November 2013.)

The International Building Code (IBC) in the occupancy chapter 304 defines testing and research laboratories as a Business Group “B” occupancy. The International Mechanical Code (IMC) in Table 403.3 identifies minimum ventilation rates for science laboratories, and section 510 explains the requirements for laboratory exhaust systems.  

There are other standards as well, such as OSHA 29 CFR 1910.1450: Occupational exposure to hazardous chemicals in laboratories and 21 CFR 58: Good Laboratory Practice Regulations, which while giving guidance, do not specifically require or specify ventilation rates or practices.

The more recent editions of several codes and standards have less focus on minimum or required air change rates and more focus on proper capture of fumes and contaminants, protection of workers, proper hood design and sash face velocity, supply air distribution, and pressure relationships. As with any project design, it is appropriate to determine which codes and standards are officially adopted by the authority having jurisdiction (AHJ) so that the correct and more stringent requirements can be incorporated into the design.

Fume hood types

Some common types of fume hoods used in clinical and chemical labs include standard fume hoods (constant volume exhaust airflow with variable face velocity) shown in Figure 1; bypass fume hood (constant volume exhaust airflow) shown in Figure 2; variable volume fume hood (constant face velocity); and auxiliary air fume hood (constant volume exhaust airflow with 50% to 70% makeup air directly to hood).

Figure 1: Standard constant volume fume hood shows a typical airflow pattern. Courtesy: Smith Seckman ReidFigure 2: A bypass constant volume fume hood shows a typical airflow pattern with sash closed. Courtesy: Smith Seckman Reid

Additionally, there are biological safety cabinets used in clinical lab settings that include Class I, which is similar to a chemical fume hood (see Figure 3); and a Class II A1 bio-safety cabinet that includes high-efficiency particulate absorption (HEPA) supply filters and HEPA exhaust filters that allow air to be re-circulated to the lab or exhausted directly outside (see Figure 4).

A Class II B1 bio-safety cabinet is similar; however, all air is removed through a HEPA filter and exhausted directly outside. A Class III bio-safety cabinet is completely enclosed and the work is done through gloves attached to the cabinet. This cabinet is exhausted directly outside with no recirculation allowed. The figures illustrate the differing airflow patterns and filtration requirements.

Figure 3: This Class I bio-safety cabinet shows a typical airflow pattern and HEPA filter location and laminar airflow. Courtesy: Smith Seckman ReidFigure 4: Class II A1 bio-safety cabinet has a typical airflow pattern and HEPA filter location with laminar airflow with clean supply and discharge air. Courtesy: Smith Seckman Reid

Generally, when working in a required clean environment such as when mixing medications (pharmacy) or working with infectious bacteria (research), airflow direction and air cleanliness are requirements. Bio-safety cabinets provide that cleanliness and direction with placement of the HEPA filters at the point of air delivery and removal. HEPA filters carry a minimum efficiency reporting value—commonly known as MERV—rating of 17 or higher.

Canopy hoods are open on the sides and primarily used to remove heat and water vapor from work areas. This hood type is not a true fume hood and should not be used as a substitute for one.

Open sash face velocities are between 75 ft per minute (fpm) and 120 fpm, with 100 fpm being an average velocity or rule of thumb for preliminary air calculations depending on what chemicals are stored or used in the hood. A velometer is attached to the fume hood to measure face velocity and inform users if the hood is safe to use. The hood sensors may alarm locally or be connected to the building automation system (BAS).

ASHRAE Standard 110: Method of Testing Performance of Laboratory Fume Hoods, defines the criteria for containment performance of a fume hood using a tracer gas and instruments to measure the amounts of tracer gas that enters the breathing zone of a mannequin. This test simulates the containment capability of the hood. A face velocity test, flow visualization test, large volume visualization test, tracer gas test, and sash movement test are all performed under this standard. The standard has specific requirements that must be met for the hood to comply.


<< First < Previous 1 2 Next > Last >>

ROB , NC, United States, 02/21/14 11:27 AM:

Although this is a very introductory article, I find some of the items outdated and troubling. Among these are: 1. By law, OSHA clearly states that face velocity cannot be used as a measurement of worker safety. 2. Lab air cannot be used to dilute or protect a worker from chemical exposure, only source control may be used. 3. ASHRAE 110 is only a procedure to determine spill rate, it is not a pass/fail test. 4. The illustrations/photos provided are of general purpose hoods that provide no protection from splash or blast in accordance with NFPA 45. 5. The use of diversity in lab design is a major cause of hood failure and worker exposure. Keep in mind the liability that remains with the designer for as long as the hood is in service.