Designing labs, research buildings: Codes and standards
Labs and research facilities house sensitive equipment and must maintain very rigid standards. Codes and standards must be adhered to, with special attention to codes unique to these buildings.
Nedzib Biberic, PE, LEED BD+C, Mechanical Engineer, PAE Consulting Engineers, Portland, Ore.
Michael Chow, PE, CxA, LEED AP BD+C, Member/Owner, Metro CD Engineering LLC, Powell, Ohio
David S. Crutchfield, PE, LEED AP, Division Manager, RMF Engineering, Baltimore
Dave Linamen, PE, LEED AP, CEM, Vice President, Stantec, Edmonton, Alberta
Jay Ramirez, Senior Vice President, ESD Global, Chicago
CSE: What challenges do you have when implementing NFPA 45: Standard on Fire Protection for Laboratories Using Chemicals?
Crutchfield: The biggest challenge we face is how to ensure differential pressures are appropriately maintained per NFPA 45 8.2.5 and 8.4.7 when the air handling and exhaust systems go into emergency modes. We’ve seen that when the lab supply fans trip in response to an alarm event, and the exhaust fans remain operational to ensure hood containment, the resulting pressurization differentials can be beyond ADA Door Opening Force Regulations (Title III Section 4.13.11) of 5 lbf. The obvious way to decrease the pressure differential is to provide for a relief pathway, but often that pathway would compromise the fire/smoke barriers surrounding the labs. Opening big holes in your architects’ carefully created fire/smoke barriers is not a good idea when there is a fire in the building. To overcome this, we’ve used transfer systems that actually open in response to an alarm event, which decreases the pressure differential between the lab and the adjacent spaces. To maintain occupant safety in this event, these openings also have local sensing elements that close the opening if products of combustion are detected. An alternative is to provide this pressure relief system such that it directly communicates with the outdoors. However, we have found that when using a direct connection to the outside in areas with coastal air (salt/wet), the dampers and sensors in the transfer system need excessive maintenance to ensure proper operation. Often during testing of these exterior coupled systems, they fail to open due to corrosion, insect nests, etc. This leads to the desire to keep the transfer equipment in a conditioned space. On this issue, we generally confer with the local authority having jurisdiction (AHJ) so that our design meets its criteria for life safety, compliance with NFPA, and compliance with ADA.
Linamen: NFPA 45 has paragraphs that require lab supply and exhaust air systems to be designed in such a way that they prevent pressures that would inhibit egress in the event either the supply or exhaust systems fail. This requires that the operation of both systems be monitored closely, and that the proper control functions be provided to adjust one system appropriately if the other fails so that excessive pressures in occupied spaces do not result. On one of our projects, the building officials actually placed both the supply and exhaust air systems in failure mode separately, and then measured the force required to open doors throughout the building, testing the controls we had provided to prevent excessive pressures in the event of an air system failure. NFPA 45 also prohibits fire dampers in fume hood exhaust systems. We usually address this on a case-by-case basis with the AHJ. Some officials require that the main exhaust duct from each floor extend all the way to the penthouse or roof in a separate fire-rated shaft, since a fire damper cannot be provided at the shaft penetration. Some will accept the sub-duct arrangement from NFPA 90A, where the horizontal main exhaust duct from each floor elbows vertically for 22-in. before connecting with the exhaust riser.
NFPA 45 also restricts the use of ductless fume hoods with absorptive filters that recirculate air to the occupied space to nuisance vapors that do not present flammable of toxicity issues. The ductless fume hood is an attractive lower overall cost alternative for many renovation applications, and this limitation helps prevent users from using the hoods in applications for which they are not intended. Finally, NFPA 45A is used to specify a given minimum flow rate of 25 cfm/sq ft of fume hood internal footprint. The latest 2011 version refers to the ANSI/AHIA Z9.5 Laboratory Ventilation standard, which limits the minimum fume hood flow rate to 150 hood ACH. This translates to a lower minimum airflow in general through hoods, and could cause issues with concentration of flammable or explosive vapors in hood exhaust if a chemical spill should occur in a hood at minimum airflow.
CSE: Which aspect of codes and standards has in your experience provided the biggest challenges or obstacles?
Linamen: NFPA 45, which prohibits fire dampers in fume hood exhaust systems and references ANSI/AIHA Z9.5 for minimum hood airflow, as well as NFPA 90A, which requires duct risers conveying environmental (supply) air from being located in the same shafts as duct risers conveying non-flammable corrosive fumes and vapors. Frequently, it is difficult to provide separate shafts for supply and exhaust air risers.
Crutchfield: NFPA 45 18.104.22.168 provides a challenge in multistory buildings. The separate exhaust shafts required for each laboratory unit, and the need to maintain the fire rating of the building, often mean that multiple sub-shafts are required in the main building shafts. This ensures that the exhaust ducts are compliant with code and also maintain the required fire separation integrity of the building. The challenge is how to build these sub-shaft assemblies in existing buildings.