When a fume hood’s certification report says it was tested to ASHRAE 110, that means something more specific than an annual face-velocity check. ASHRAE 110 (formally ANSI/ASHRAE Standard 110, Method of Testing Performance of Laboratory Fume Hoods) is a laboratory test method — a defined, repeatable procedure for measuring how well a hood actually contains a hazardous release, not a set of pass/fail limits imposed by a regulator. It is the test protocol that ANSI/AIHA Z9.5 (the broader laboratory-ventilation management standard) and many institutional Chemical Hygiene Plans point to when they call for containment testing beyond a simple face-velocity reading. This guide explains what the ASHRAE 110 method actually measures, how the three parts of the test work, what AM/AI/AU designations mean, and where it fits alongside the routine annual certification most labs already know.
ASHRAE 110 vs. Routine Face-Velocity Certification
Most institutions’ annual fume hood certification — covered in CASRAI’s Chemical Fume Hood Certification and Inspection guide — centers on measuring average face velocity across the sash opening with a calibrated anemometer, plus a qualitative smoke check for obvious reverse flow. That test is fast, inexpensive, and appropriate for a routine annual cycle, but face velocity alone is an indirect proxy for containment: two hoods with identical average face velocity readings can perform very differently when a real vapor release happens inside them, depending on cabinet geometry, baffle design, and turbulence at the sash.
ASHRAE 110 goes further. Instead of only inferring containment from an airflow-speed number, it directly measures whether a simulated contaminant released inside the hood actually reaches a person standing at the sash opening, using a tracer gas and a detector positioned at the user’s breathing zone. It is the more rigorous, more instrumented, and more expensive of the two test approaches — not a replacement for annual face-velocity certification, but the method used for commissioning new hoods, evaluating hood models, and periodic containment verification for higher-hazard or higher-scrutiny applications.
The Three Parts of the ASHRAE 110 Test
1. Face velocity
As with routine certification, the test begins by measuring average face velocity across a grid of points on the sash plane at a specified working sash height, confirming the hood is operating within its intended airflow range before the more detailed tests proceed.
2. Flow visualization (smoke test)
A visible smoke source is used at the sash opening, along the hood’s interior surfaces, and around the perimeter of the opening to visually confirm air is flowing smoothly inward with no reverse currents, dead spots, or turbulent escape paths. This step catches airflow problems — a recirculating eddy at a back corner, spillage around the sash frame — that a single average face-velocity number can mask entirely.
3. Tracer gas containment test
This is the part that distinguishes ASHRAE 110 from ordinary certification. A tracer gas is released at a controlled, constant rate from a small diffuser positioned inside the hood, simulating a contaminant source at working height. A gas detector samples air continuously at the breathing zone of a life-size mannequin positioned at the hood’s sash opening, typically while the mannequin (or the detector sampling around it) is swept across the width of the opening to check containment across the full face, not just at one point. The resulting measurement — the concentration of tracer gas detected at the mannequin’s breathing zone — is the test’s actual containment result, reported in the certifier’s report, generally alongside a stated pass/fail threshold set by the standard’s rating scale or by the institution’s own adopted criteria. Because this step requires calibrated gas-detection instrumentation and a trained tracer-gas certifier, it is typically performed less frequently, and by a more specialized certifier, than routine annual face-velocity checks.
AM, AI, and AU: The Three Test Conditions
ASHRAE 110 defines three distinct test conditions, each answering a different question about the same hood:
- AM — As Manufactured. Tested by the manufacturer under controlled factory conditions before the hood ships, with no installation-specific ductwork or building airflow variables in play. This is the baseline performance figure a manufacturer publishes for a given hood model.
- AI — As Installed. Tested after the hood is physically installed and connected to the building’s real exhaust and supply air system, with the sash static (not moving) and no simulated operator activity. AI testing verifies that the specific installation — ductwork routing, blower sizing, room air balance — hasn’t degraded the hood’s containment relative to its AM rating. This is the test most commonly performed at commissioning, before a newly installed hood is released for use.
- AU — As Used. The most demanding condition: tested with simulated operator movement in front of the hood — typically a mechanized arm or robotic apparatus that repeatedly moves into and out of the hood opening, mimicking a person reaching in to manipulate equipment. Because operator movement is a major real-world source of turbulence and containment loss, AU results are consistently the most conservative (and most representative of actual working conditions) of the three ratings, and are the condition most relevant to whether a hood protects its user during genuine day-to-day work.
A hood can pass an AI test cleanly and still show meaningfully worse containment under AU conditions purely because of operator movement — which is why AU testing, though the most resource-intensive to run, is the condition institutions with higher-hazard fume hood use (perchloric acid work, highly toxic or carcinogenic reagents, radioisotope work) are most likely to require periodically rather than relying on AI results alone.
How the Result Is Reported
A certifier’s ASHRAE 110 report states, for each condition tested, the maximum tracer gas concentration detected at the mannequin’s breathing zone during the test, generally expressed in parts per million (ppm). Lower is better: a well-performing hood keeps the detected concentration very low (commonly cited institutional benchmarks target a maximum on the order of a few hundredths of a ppm for the containment result to be considered good performance), while a hood with a containment problem shows detectable, sometimes substantially higher, tracer gas concentrations reaching the breathing zone. Exact pass/fail numeric thresholds vary by institutional policy and by which edition and rating convention the certifier’s report follows — when reviewing a report, treat the certifier’s stated pass/fail criterion, not a number recalled from memory, as authoritative, and confirm your institution’s Chemical Hygiene Plan documents which threshold it has adopted.
Who Performs ASHRAE 110 Testing, and When
Because the tracer-gas portion requires specialized gas-detection equipment, a controlled release apparatus, and training most in-house EHS teams don’t maintain year-round, ASHRAE 110 testing (particularly the AI and AU tracer-gas steps) is frequently contracted to a specialized third-party fume hood testing firm rather than performed by the same staff who run routine annual face-velocity certification. Typical triggers for an ASHRAE 110 test include:
- Commissioning a newly installed hood — an AI test before the hood is released for use, confirming installation didn’t compromise the manufacturer’s AM performance.
- Evaluating or comparing hood models before purchase, using published AM ratings.
- Periodic containment verification for higher-hazard applications, where an institution’s policy calls for tracer-gas (rather than face-velocity-only) testing on a defined cycle — often less frequent than the annual face-velocity cycle, because of cost and the specialized labor involved, but performed specifically because face velocity alone is judged insufficient assurance for that use case.
- After a significant HVAC or ductwork change, where the institution wants direct containment evidence rather than relying on a face-velocity re-check alone.
- Investigating a suspected containment failure — an odor complaint, an exposure incident, or a face-velocity test result close to a limit — where a full tracer-gas test gives a more definitive answer than re-measuring face velocity.
Where ASHRAE 110 Fits in Your Chemical Hygiene Plan
OSHA’s Laboratory Standard (29 CFR 1910.1450) requires that fume hoods be maintained and function properly, and points institutions to a recognized consensus standard rather than prescribing a specific test method itself. ANSI/AIHA Z9.5, the standard most U.S. institutions actually test against for routine certification, references ASHRAE 110 as the method for the more rigorous, instrumented containment testing it recommends beyond basic face velocity — particularly for commissioning and for higher-hazard hood use. A well-written Chemical Hygiene Plan should name which testing method applies to which situation: routine annual face-velocity certification under Z9.5 for the general hood population, and ASHRAE 110 (specifying AI or AU) for commissioning and for any hoods designated higher-hazard by institutional policy. See CASRAI’s Chemical Hygiene Plan training and OSHA requirements guide for how this fits into the broader written-plan and training obligation.
Reading an ASHRAE 110 Report: What to Check
- Which condition was tested — AM, AI, or AU. A report that only states an AM rating (the manufacturer’s factory figure) tells you nothing about how the specific installed hood is performing in your building; confirm the report reflects an AI or AU test actually run on your hood.
- The stated pass/fail criterion and whether the measured result met it, not just a raw ppm figure without context.
- Sash position tested — results at the posted working sash height are what matters for normal use; a hood tested only at a partially open sash may perform differently at full sash height.
- Date and next-due date, and whether the testing interval matches what your institution’s Chemical Hygiene Plan actually specifies for that hood’s hazard designation.
- Certifier qualifications — confirm the firm or individual performing tracer-gas testing is trained and using calibrated equipment; this is specialized testing, and not every fume hood certification vendor offers the tracer-gas portion.
Frequently Asked Questions
What is ASHRAE 110 fume hood testing?
ASHRAE 110 (ANSI/ASHRAE Standard 110, Method of Testing Performance of Laboratory Fume Hoods) is a standardized test method that measures a fume hood’s actual containment performance using three components: face velocity measurement, a smoke flow-visualization test, and a tracer gas containment test that measures how much simulated contaminant reaches a mannequin’s breathing zone at the hood face. It is more rigorous and more instrumented than routine annual face-velocity certification.
What is the difference between AM, AI, and AU ASHRAE 110 ratings?
AM (As Manufactured) is the manufacturer’s factory test under controlled conditions before shipment. AI (As Installed) tests the hood after installation in its actual building ductwork, with the sash static and no simulated operator movement. AU (As Used) adds simulated operator movement in front of the hood, representing the most realistic and typically most demanding test condition.
What tracer gas is used in ASHRAE 110 testing?
The standard’s tracer gas test releases a detectable gas at a controlled rate inside the hood and measures its concentration at a mannequin’s breathing zone using calibrated gas-detection instrumentation. Certifiers should document which tracer gas and detection method their specific test used in the report, since instrumentation and tracer choice can vary by certifier and by equipment available.
Is ASHRAE 110 testing required by OSHA?
OSHA’s Laboratory Standard (29 CFR 1910.1450) requires fume hoods be maintained and function properly but does not name a specific test method itself; it defers to recognized consensus standards. ANSI/AIHA Z9.5, the standard most U.S. institutions use for their testing program, references ASHRAE 110 as the method for containment testing beyond routine face velocity, particularly for hood commissioning and higher-hazard applications — so ASHRAE 110 testing becomes a practical requirement wherever an institution’s own Chemical Hygiene Plan adopts Z9.5’s recommendations, even though it is not directly named in the OSHA regulation.
How is ASHRAE 110 different from the annual fume hood certification most labs already do?
Routine annual certification typically measures face velocity and does a basic smoke check. ASHRAE 110 includes those same two steps but adds a full tracer gas containment test measuring what actually reaches a user’s breathing zone, under AM, AI, or AU conditions. Because of the specialized equipment and labor involved, ASHRAE 110’s tracer-gas component is usually performed less frequently than annual face-velocity certification, at commissioning, or for hoods an institution designates higher-hazard.
