35.2 Contaminants, Source Control, TAB & Human Health Effects

35.2 Contaminants, Source Control, TAB & Human Health Effects

The rest of Trade Area I (3 percent Class A / 4 percent Class B) is what is in the air, how you stop it at the source, whether the outdoor-air path actually flows, and what poor air does to occupants. Section 35.1 hung the OA damper, the filter, the dehumidifier, the UV-C lamp, and the electronic air cleaner. This section is the complaint, the code return, the condensate pan, the TAB sheet, and the words you are allowed to use about health. The same 2026 books apply: FBC Mechanical 2023 (Chapters 3, 4, and 6), FBC Energy Conservation 2023, Refrigeration & Air Conditioning Technology, 9th Edition (2021), and the instruments already used in Sections 22.4 and 30.3 (pitot, manometer, flow hood). Class B still cannot contract a 30-ton plant, but a 4-ton attic that returns garage air, overflows a pan, and never measured OA is a Class B Trade I failure.

Quick Answer: Source control first, then dilution, then filtration. 601.5 keeps return out of the garage and the bath. A wet 307 pan is a moisture source. TAB the outdoor-air cfm; mixed-air temperature estimates percent OA. CO2 is an occupancy proxy, not a 1,000 ppm poison test. Describe occupant effects as irritation, odor, stuffiness, moisture damage, and CO hazard — not as unpublished disease statistics.

Name the contaminants before you buy a gadget

Indoor air is a mixture. Trade I items group the mixture so you pick the right control, not so you practice medicine.

Do not treat pollen, CO2, and carbon monoxide as the same problem with one MERV 13. Particles need capture. Gases need source control and outdoor air. Moisture needs a coil below dew point and a drain that leaves the building. Carbon monoxide needs combustion that vents and a garage that is not the return plenum.

Source control, then dilution, then filtration

The control order the exam wants is the order that actually works:

1. Source control — stop generating or stop entraining the contaminant.
2. Dilution — outdoor air (Section 35.1) sized from people + area.
3. Filtration / air cleaning — capture what is left, within the fan’s static budget.

FBC Mechanical 601.5 is the source-control return-air list. Return air shall not be taken from closets, bathrooms, toilet rooms, kitchens, garages, mechanical / furnace rooms, unconditioned attics, or unconditioned crawl spaces, except as the section’s listed exceptions allow (a dedicated garage HVAC system, a kitchen return kept away from cooking appliances, a closet that is only an air-handler room with the required clearance, and similar). A jumper grille from the house into the garage, a return boot in a bath, or “borrowing” attic air because the return is undersized, puts the contaminant into the supply. That is not an IAQ upgrade. 401.4 is the same idea at the outdoor-air intake: 10 feet horizontally from vents, chimneys, plumbing vents, streets, alleys, parking lots, and loading docks unless the code’s vertical exception applies.

Other source-control moves that show up next to HVAC: keep paint and fuel in closed containers; isolate a janitor’s closet from the return; do not idle a truck at the OA hood; combustion appliances that spill need draft and listing, not a bigger filter. F.S. 489.105 still fences gas fuel lines within buildings on changeouts (disconnect/reconnect only). It does not fence the duty to keep garage air out of the house. NFPA 90A / 90B still want listed devices in the airstream and access to service them — a filter you cannot pull is not source control.

Dilution without source control is expensive outdoor air used as a deodorant. Filtration without source control loads the media and does nothing to CO or water vapor. Pearson VUE loves the contractor who sells a UV lamp and an EAC while the return is in the garage and the pan is a swamp.

Condensate as a moisture source

Florida latent load keeps evaporator pans wet for months. Warm, dark pans grow biological slime and algae; that growth is both a bioaerosol source when air washes the pan and a plug that turns the pan into a pool. Overflow then wets the attic, the ceiling, and sometimes the supply airstream. Trade F (Section 32.3) already cleaned the line. Trade I asks you to see the pan as IAQ, not just a callback.

FBC Mechanical 307.2.1: convey condensate to an approved place of disposal at a slope of not less than 1/8 inch per foot. 307.2.1.1: no direct connection to the sanitary DWV. Table 307.2.2: drain not less than 3/4 inch through 20 tons. 307.2.3: where overflow would damage the building (Florida attics and second-floor air handlers), provide an auxiliary pan with a conspicuous drain, an equipment overflow drain, or a UL 508 water-level device that shuts the equipment off. Downflow coils (307.2.3.1) take that device in the primary pan, not in the drain line. 307.2.5: the line must be clearable without cutting. A secondary pan full of sludge is not overflow protection. A wet pan with a dead float is a moisture source still in the air handler.

Standing water on coil fins, in the pan, or in a carpet under a supply boot is how mold grows on building materials. The honest contractor statement is: keep materials dry, drain the condensate out of the building, and keep occupied RH from sitting above about 60 percent. That is not a medical diagnosis.

TAB of ventilation airflows

Section 22.4 already taught testing, adjusting, and balancing with pitot, velometer, and flow hood, and the standard-air velocity equation (V \approx 4005 \times \sqrt{VP}). Trade I uses the same instruments on the outdoor-air path, not only on the supply total.

If the rooftop is delivering 2,000 cfm of supply, that number does not prove 400 cfm of outdoor air. Measure OA separately: a traverse of the OA duct, a flow station, or a hood on an OA grille. A DDC graphic that displays 400 cfm because the damper command is 20 percent open is not a TAB reading.

When outdoor and return dry-bulbs differ — Florida summer is the easy case — mixed-air temperature estimates the OA fraction:

(%\text{OA} \approx (T_{mix} - T_{return}) / (T_{outdoor} - T_{return}))

Worked mixed-air example. Design OA is 400 cfm of a 2,000 cfm supply (20 percent). Outdoor 95°F, return 75°F. Mixed air should be (75 + 0.20 \times 20 = 79°F). The TAB tech reads 77°F mixed. (%OA = (77 - 75) / (95 - 75) = 10%). Actual OA is about 200 cfm. The building is under-ventilated even if every supply grille hit its schedule. Causes: OA damper pinned, economizer blade off its stop, dirty OA hood, or a fan that cannot pull OA against a loaded filter (Section 35.1 MERV tax).

Building pressure is the other TAB number. Exhaust without makeup pulls the building negative. In Climate Zones 1A/2A, negative means humid outdoor air infiltrates through the envelope, condenses on cooled gypsum, and grows mold in places the filter will never see. The usual Florida strategy is slightly positive with dehumidified outdoor air — not a window cracked as “makeup,” and not bath fans that run 24/7 against a sealed OA damper. Kitchen makeup still follows Chapter 22.3 (approximately equal to exhaust, interlocked, must not wreck capture). That makeup is source control plus ventilation, not a MERV problem.

CO2 as an occupancy proxy — not a toxin test at 1,000 ppm

People exhale carbon dioxide. Outdoor air is on the order of 400-plus ppm. Indoor CO2 rises when OA per person is low. Demand-controlled ventilation uses that rise to open the OA damper toward the 62.1/FBC rate when the room fills, and to cut toward the code floor when it empties. That is a ventilation control, and it is legal only if the floor still ventilates an occupied zone.

What CO2 is not: a contaminant you “solve” with a filter or a UV lamp; a medical pass/fail at 1,000 ppm; immediately dangerous to life at ordinary indoor levels. OSHA’s 8-hour permissible exposure limit for CO2 is 5,000 ppm time-weighted average. Older comfort discussions used about 1,000 ppm as a ventilation indicator tied to odor and perceived stuffiness, not as a poisoning threshold. Do not tell a board that 1,000 ppm is IDLH. Do not ignore a 2,000 ppm conference room either — that room is under-ventilated, which is the Trade I point.

Carbon monoxide is a different molecule. CO from incomplete combustion or an attached garage is a known toxic gas that can cause headache, nausea, and death. Source control (vented appliances, 601.5, 401.4) and listed CO alarms per the building code are the response. An EAC does not collect CO.

Human health effects — say only what the exam can defend

The outline asks for effects of poor air quality on humans. Stay with established, non-invented effects:

• Irritation of eyes, nose, and throat; dryness or burning from very dirty or very dry air; occupant odor complaints (musty, chemical, exhaust).
• Stuffiness, headache, and fatigue associated with inadequate outdoor air (the CO2-proxy situation), not a claim that CO2 at 1,000 ppm is the toxin.
• Moisture and mold on building materials when RH stays high or when condensate wets gypsum and insulation. Occupants may report musty odor and irritation. People who already have asthma or allergies are often more sensitive to dust, pollen, and damp interiors. That is an EPA-level qualitative statement. It is not a contractor diagnosis, a published infection rate, or a promise that MERV 13 “treats” asthma.
• Carbon monoxide poisoning risk from combustion spillage and garage interconnect — colorless, odorless, can be fatal.
• Ozone from some ionizers and from 185 nm UV is itself a lung irritant. Use listed UL 867 EACs and ozone-free HVAC UV lamps.

Do not invent cancer percentages, “sick building syndrome” as a single disease, COVID removal claims, or a ppm of mold that “proves” illness. The CILB item is: poor IAQ bothers occupants, moisture grows mold on wet materials, CO can kill, and the contractor’s job is source control, ventilation, humidity control, and listed air cleaning — not a medical practice.

Florida HVAC scenario

Orange Park Comfort, a certified Class B shop, is called to a 3,000-square-foot office (well under 25 tons) where staff report headaches, eye irritation, and a musty smell. Supply totals on the last TAB sheet matched the RTU nameplate. The tech finds: a return grille in the adjacent garage storage bay; an OA damper at 5 percent with mixed air 76°F on a 94°F afternoon (return 75°F → about 5 percent OA); bath exhaust running against that damper so the suite sits negative; a primary pan full and a float switch taped; indoor RH 68 percent at 74°F. Five Trade I hits in order: (1) source control — 601.5 forbids that garage return; (2) TAB of ventilation — nameplate supply is not OA; mixed-air math shows the damper is lying; (3) building pressure — negative in Zone 2A pulls humidity into the envelope; (4) 307 — standing water is a moisture/bio source, and a taped float is not 307.2.3; (5) health language — irritation, odor, and stuffiness from under-ventilation and dampness, not a speech about unpublished mold toxins. Adding MERV 13 and a UV lamp while those five sit is the exam’s wrong answer.

Traps: (1) Filtration first, source control never. (2) Supply cfm treated as outdoor air. (3) 1,000 ppm CO2 called immediately dangerous. (4) Negative building as a Florida humidity strategy. (5) Inventing a medical statistic to sell a lamp.