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Rev 007 8/26/2008

Lab Ventilation- Air Changes in Laboratories

Executive Summary:

Laboratories are complicated spaces with significant infrastructure designed and operated to

allow researchers to work safely with a vast and dynamic array of hazardous materials. EH&S

does not endorse a standard air change rate (Air Changes/ Hour, ACH); instead it supports a

collaborative, site-specific process among building users knowledgeable in all planned work,

lab designers, and EH&S to establish the most efficient and effective ventilation design. The

air change rate in a laboratory building is not as important as: the proper design, operation and

maintenance of the building HVAC system; researchers access to appropriate dedicated

exhaust systems (fume hoods, biosafety cabinets, slot hoods, for example); proper

programming of space for specific type of research; the ability of researchers to use built-in

controls coordinated with safe practices; and, the flexibility of the buildings design to support

renovations and alterations, ultimately allowing research to be conducted in a safe manner.

Reduced ACH capacity will require increased operational controls and surveillance to respond

to new users and processes. Designing or limiting air change rates to absolute minimums may

reduce a buildings capacity to the point where future research flexibility or expansion is

compromised.Air changes per hour (ACH), is a simple calculated rate of how often the air in a total volume

of a space is exchanged. Another rate discussed is actual or effective air changes per hour,

which is the actual air exchange rate and includes short-circuiting of air and other limitations to

actual system function.

Although the air change rate is one of the most commonly discussed numbers in lab

ventilation, typically it is neither a useful measure of lab ventilation effectiveness nor a

measure of occupant protection. There is no known correlation between lab ACH and

disease. Labs are particularly complex facilities which must be designed and maintained for

working safely with hazardous chemicals, biological agents, radiological materials and

physical hazards.

Protecting the health and safety of lab personnel is the first priority, and, as stated above, doesnot necessarily correlate with ACH. Air changes per hour alone is not as important a safety

consideration as the control of hazardous emissions at the source during both commissioning

and the inevitable changes that will occur over the life of the building. The joint goals of

safety and efficient use of energy and resources require thoughtful design, trained researchers

who apply appropriate hazardous material control techniques, and skilled facility managers

who understand and operate ventilation systems with great care. Reducing the number of fume

hoods or other dedicated exhaust equipment in a lab can cause research staff to conduct

activities with hazardous materials on the open bench instead of a fume hood and drive the

need for a potentially higher ACH rate (if hazardous emissions are not captured at their source

they will be diluted by general exhaust).

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The following are standards, guidelines and codes related to laboratory ACH. Rev 007 8/26/2008

Standard/Guideline Recommended Air-Change Rate

ANSI/AIHA Z9.5-2003 The specific room ventilation rate shall be established or

agreed upon by the owner or his/her designee.

NFPA-45-2004 Minimum 4 ACH unoccupied, occupied typically greater

than 8 ACH.

ACGIH Ind. Vent 24th Ed., 2001 The required ventilation depends on the generation rate and

toxicity of the contaminant not on the size of the room in which it occurs.

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ASHRAE Lab Guide-2001 4-12 ACH

OSHA 29 CFR Part 1910-1450 4-12 ACH

Code Ventilation Rate Comment

IBC 2004 1 CFM/ft2 for H-5 Section 415.9.2.6

IMC 2004 1 CFM/ft2 Rate required for storage areas that

exceed maximum allowable quantities of Hazardous materials. Section 502.8.1.1.2

UBC 1997 1 CFM/ft2 for H-6 Uniform codes have been

replaced by International codes beginning in 2000. Section 1202.2.5

OSHA 29 CRF 1910.106 (d)(4)(iv) 6 AC/HR Flammable storage rooms.

Design and Use Considerations:

The preceding table reflects a lack of consensus among standards for ACH in laboratories.

More important than the ACH is the overall effectiveness of the buildings ventilation. In the

laboratory, factors that influence ventilation rates include:

Toxicity and properties of a wide range of hazardous materials in use (chemical,biological, radiological); Rev 007 8/26/2008

Availability and use of local ventilation capture (e.g.: direct venting of equipment, slot

or canopy exhaust);

Work practices in the lab (is all hazardous material work performed with local exhaust

ventilation designed for the specific tasks, or is it performed on the open bench?);

Use of gases, volatile liquids and fine powders or aerosols requires specialized exhaust.

Fume hoods have been used in the past. In some cases gas cabinets, equipment

enclosures and other specialized exhaust devices are necessary to control these

materials;

Is the space occupied and can that determination be made with a high degree of

certainty and with feedback to the HVAC system? What is the potential for chemical release, either through non-ventilated, non-enclosed

procedures or spills?

Have the lab spaces been programmed (i.e.: the process ofcoordination of layout of

equipment, infrastructure, and furnishings to suit the activities to be conducted within

the space) with knowledge of, and attention to, the specific type of research and the

needed density and hood size both for the current program and occupants and future

research activities, materials and equipment, and inevitable changes to research

methods?

What is the intended life of the building?

What operational procedures and controls are in place to verify that hazmat use is

evaluated as part of the current and future space re-allocation processes?

Control contaminants at source. One of the tenets of good EH&S design is the

principle of capturing materials at their source to prevent exposure. It is much more

efficient to capture a hazardous material in a fume hood, for example, instead of

ventilating the entire lab at a higher rate.

Process to identify safer substitutes for toxic materials whenever possible

Ongoing training program for all existing and future occupants

Compliance with procedures and requirements by all occupants;.

Continuous evaluation and hazard assessment by expert hygienists and other resources.

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Flexibility and design capacity to adequately respond to changes in current and future

uses.

Certain occupancies (i.e. chemical storage) allow no ventilation set backs. When no

occupancy setbacks (e.g.: nighttime) are installed, they must have conspicuous visual

feedback panels to communicate system status that can be overridden.

Prior approval required for any change in materials and work.

Minimum ASHRAE 62 requirements for fresh air

Minimum ASHRAE 55 recommendations for thermal comfort

Meeting fume hood performance set forth by ASHRAE 110 or a variation thereof.

Research access to adequate fume hoods/enclosures/Local Exhaust Ventilation

Restrictions for Lab/Building must be determined and communicated.

Best Practices: Current best practices for lab design include:

Construct a working mockup for unique situations or energy saving innovations

Perform Computational Fluid Dynamics modeling of supply and dedicated exhaust and

effective air changes

Conduct computer and wind-tunnel receptor modeling for all new facilities studies.

Model occupant exposure for hazardous equipment or activities Rev 007 8/26/2008

Conclusion:It is not prudent to specify an air change rate for a building by policy or guideline. Instead,

this decision must be based on site-specific information about the various spaces and intended

uses of the areas. A more appropriate design goal is: What ventilation considerations will be

necessary to enable current and future users of this space to work safely? That question may

be answered only after extensive programming and inter-disciplinary collaboration among

users, building designers, building operators, and environmental health and safety

professionals.