When A2L Meets the Electrical Room

While reviewing the project’s mechanical submittals, I noticed something unusual. All units were supposed to be R-410A, but a few had been changed to A2L refrigerant.

 

At first, I thought it was just a simple model revision. Then I followed the list and saw where those units were going. One of them was assigned to the MDF/MPOE room. That’s when it clicked. A2L... mildly flammable... things get different when that goes into an electrical room.

 

I remembered what I’d read before. A2L isn’t the same as R-410A.

According to ASHRAE 34, R-410A falls into the A1 safety group “A” for low toxicity and “1” for non flammable under normal operating conditions. In short, it’s the reason most commercial HVAC systems have safely used R-410A for years without additional protective systems. But R32, “Mildly flammable” literally means what it says. Once that refrigerant enters a space filled with electrical equipment, extra safety measures aren’t optional anymore, they’re mandatory.

 

What Exactly Is an MDF/MPOE Room?

The MDF (Main Distribution Frame) and MPOE (Minimum Point of Entry) might sound like simple telecom spaces, but in reality, they’re the neural center of a building where electricity and data intersect. The MDF is the main hub where external communication lines like internet, phone, and data, first enter the building and get distributed to each floor.

 

The MPOE, on the other hand, is the entry point that connects the building directly to the service provider’s network.
Both are usually housed in the same room, where power panels, UPS units, switching hubs, and network racks are installed together.

 

In other words, it’s not just a communication room. It’s a hybrid electrical space packed with high density electronic equipment, power distribution panels, and tangled network cabling.

 

Physical Characteristics of This Space

The environmental conditions inside this room are completely different from an ordinary office space.

 

High Heat Load.
Network racks, servers, UPS units, and switching hubs operate 24/7. Each generates continuous heat, which is why these rooms require constant cooling, not comfort cooling, but operational cooling.

 

High Sealing and Limited Ventilation.
For security and dust control reasons, there are no windows, and air exchange with the outside is minimal.
In many cases, even the door gaps are sealed effectively making it a confined or sealed space.

 

Uneven Air Circulation.
Hot air accumulates near the ceiling while cooler air stays near the floor. This stratified condition means that any leaked gas could pool or stagnate in certain areas instead of dispersing evenly.

 

 

Code Classification: “Critical Electrical Space”

According to CMC, and ASHRAE standards, spaces like these are treated as critical electrical environments when flammable refrigerants are present.

 

CMC 2022

According to CMC 2022 Section 320.4, MDF/MPOE rooms (telephone and technology equipment centers) require cooling but not mechanical exhaust unless specified by the equipment manufacturer.

https://epubs.iapmo.org/2022/CMC/index.html

 

ASHRAE 34

ASHRAE 34 Section 6.1 classifies R-32 as an A2L refrigerant "low toxicity and mildly flammable"

 

ASHRAE 15
Section 7.3 defines the Maximum Allowable Limit (MAL) as 0.44 × LFL, which sets the maximum charge a space can safely contain.
Section 7.4 specifies that when the refrigerant charge exceeds this limit, the space must be classified as a machinery room and equipped with required safety controls.
Sections 8.11 and 8.12 further require leak detection and automatic emergency ventilation when A2L refrigerants are used in confined or machinery spaces.

https://www.ashrae.org/technical-resources/standards-and-guidelines

 

The Core Issue, R-32 Is an A2L Refrigerant

Once an A2L refrigerant is introduced, several safeguards automatically come into play:

• Leak Detector
  Detects when the refrigerant concentration in the room exceeds a certain threshold. Because A2L refrigerants are heavier than air and tend to settle near the floor, sensors must be installed low and close to the equipment rather than on the ceiling.
  (Referenced in ASHRAE 15 2019 Section 8.11.6 and Section  8.11.8 “Refrigerant Detection and Response.”)
• Emergency Exhaust Fan
  When a leak is detected, the exhaust fan must automatically start at high speed to dilute the refrigerant and prevent the room from reaching flammable levels.
  (Referenced in ASHRAE 15 2019  Section  8.11.11 Section  8.11.14  “Mechanical Ventilation and Level 2 Ventilation.”)
• BMS Integration
  The leak detector must be tied into the building management system:
  Detector → BMS → Exhaust Fan Override + Unit Power Shutdown.
  Only when this logic chain is complete does the system qualify as a proper “automatic mitigation response.”
  Detection alone isn’t enough, ventilation and shutdown must follow immediately.
  (Referenced in ASHRAE 15 2019  Section  8.11.6.2 and Section  8.11.7 “Automatic De-energization and Remote Controls.”)
• A2L Warning Signage
  Every person entering the space must be aware of the refrigerant class. Labels such as “Contains A2L Refrigerant Mildly Flammable” must be clearly posted, as required by UL 60335-2-40 and the appendices of ASHRAE 15-2019 Section 9.17  “Marking and Labeling.”
  https://www.hvacinformed.com/news/understanding-ul-60335-2-40-standard-co-1668171588-ga.1715243565.html

 

The Supervisor’s Comment “No Exhaust Fan Needed If It’s Under 6.6 lb”

When I brought this issue up to the team, my supervisor immediately responded:

“If the refrigerant charge is under 6.6 pounds, you don’t need an exhaust fan”

At first, I wasn’t sure.
Could that possibly be written anywhere in the code?
I dug out and according to CMC 2022 Section 1106.1.1, a machinery room is required only when the refrigerant charge exceeds the limits defined in Table 1102.3. Section 1106.2.5 further specifies that leak detection and automatic emergency ventilation apply exclusively to such classified machinery rooms, not to standard equipment rooms with smaller refrigerant quantities.

 

According to ASHRAE 15 Table 7.3,
R-32 has an LFL (Lower Flammability Limit) of 0.307 kg/m³ (0.019 lb/ft³).
By definition, the Maximum Allowable Limit (MAL) = LFL × 0.44,
which equals 0.135 lb/ft³.

That value defines how much refrigerant a space can safely contain before it crosses into “Machinery Room” territory.

For our MDF/MPOE room (13 ft × 16 ft × 9 ft = 1,872 ft³):

0.135 × 1,872 = 252 lb

The system’s charge of 6.6 lb was just a fraction of that, about 2.6% of the threshold, meaning the safety margin was over 40 times larger than required by code.

 

And that “6.6 pound” figure wasn’t arbitrary. Most mini split systems ship with around 3 lb of factory charged refrigerant. Even with an extended lineset, the total charge rarely exceeds 6 lb. So from a practical standpoint, it’s nearly impossible for such a system to approach the MAL threshold. In other words, even under the most conservative assumptions, an MDF/MPOE room equipped with a single 18,000 BTU mini split system would still remain well below Machinery Room classification, no leak detector, no exhaust fan, and no override logic required.

 

 

That night, I slept like a baby.