What Are Those Black Marks Around Air Vents?

It is common for offices and homes to have black marks surrounding the vents on the ceiling. Sometimes this is misattributed to mould, but is usually a sign that there is fine particulate present in the air. It gathers around ceiling vents due to static electricity, air flow and the condensation of water.

Particulate Inside the Building

Fine particulate is usually expected to be removed with a good air conditioning system or an air exchange system, such as HRV. For the system to work effectively, it must have:

• Filters in the air exchange (air conditioning or HRV) system,
• The correct filters (ones that remove fine particulate)
• No leaks or bypasses to the filters
• No blockages in the filters (low flow, high back pressure is a sign of blockages)

Indoor air quality is an important factor in maintaining a healthy and comfortable environment. Poor air quality can affect our health and performance. Therefore, the purpose of ventilation is to remove stale air and replace it with fresh, clean air with minimal toxins.

Symptoms of Bad Air Quality

Sometimes marks will be seen streaking out the sides of supply vents on an air conditioning system. These are a sign there is an issue with the system.

• When air flows into a ventilation system it can create a static electricity charge over areas where the air flows inwards or outwards
  • Any particles in the air will be attracted to these charged surfaces
  • Low humidity will also increase static electricity
• If there are improper seals in the ceiling duct, it can allow unfiltered air to be drawn through from the roof space and then allow air to travel over the ceiling (Figure 3)
• Particulate can accumulate in the path of the air
• This suggests that there is elevated particulate either in the room or in the air flow, that can be from multiple sources
• The faster the velocity of the air flow coming in/out of the vent, and the more particles present in the air, the more defined the black markings will be on the ceiling
• Moisture in the air condition system is produced as a result of condensation, which can allow for mould growth with the combination of water and dust particles

Fans

• As a result of ceiling fans moving at high velocities, particulate in the air is more likely to accumulate on vanes (Figure 4)
• To avoid this, regularly clean fan vanes, or have fans operating at lower velocities, and reduce particulate levels in the air

Where Does the Particulate Come From?

Air Pollution

• Common sources of particulate in an office or home can be from both outside or inside
• If a room has a layer of particulate settled on surfaces, it is expected that this particulate will get caught on the wall where there is moisture or static electricity
• It is important to keep inside sources of particulate low to avoid wall streaking and related health effects such as asthma-like symptoms
• It is important to ensure your supply duct from outside is above roof height to avoid sucking in stale/polluted air that has been trapped on the roof

Fumes From Vehicles

• If an office or home is close to a road, it is possible that a proportion of the particulate is black carbon from diesel exhaust
• The black colouration around the air vents also indicates that the filters are not successful in removing all particulates from the room
• This may also be a result of the supply duct outside being too low, and sucking in stale air into the room, or having windows open that brings in fumes

Photocopiers/Printer

• If an office is not close to a road, the supply duct is above roof height and there are no significant levels of visible particulate indoors, then it may be coming from a printer or photocopier
• Photocopiers and printers can emit ultra-fine particulate, which are easily inhaled and capable of entering the human blood stream due to their small size
• Ensure there is adequate ventilation around the photocopiers/printers and move them to less crowded areas in an office

Smoking and Vaping

• If a smoking area is close to open windows of the office or home, then smoking fumes may be a source of the black marks occurring around the air vents
• It may also be coming through the supply vents outside, if they are too low
• Smoking areas should be moved far from the building and vents
• Vaping can generate ultra fine particulate

Thermal Tracking

• Thermal tracking, also called “ghosting”, is the dark stain on walls that follow the ceiling and wall framing. It can be confused with streaking, but is not the same thing
• Structural framing members such as studs or beams are the coldest part of the wall. So stains may mark the location of the framing members

How Does It Happen?

• It occurs when there are insulation issues, making the areas directly underneath the framing cooler than the rest of the wall
• The air in the building carries moisture and particulate and as the warm, damp air touches a cold spot on the wall, condensation forms
• Fine particulate adheres to the damp wall surfaces, leaving thermal tracking stains
• Air circulation problems, inadequate insulation and other structural problems can cause wall condensation, but the stains are caused by dirt inside ductwork, dirty heating units and improper combustion of appliances
• Stains such as these may be present even in homes without moisture problems
• Thermal tracking is a sign that energy is being wasted in the heating or cooling season

Associated Health Effects

• Fine and ultrafine particulates can trigger
  • Asthma like symptoms,
  • Eye and throat irritations,
  • Continuous sneezing
  • Difficulty breathing
  • Dry eyes
• There are other sources of the streaking that can have additional health effects

How Can We Find Out The Problem?

Inspections should be carried out in the following places:

• Areas recently renovated
• Areas where there have been complaints
• The mechanical equipment room

Questions To Consider During An Inspection

The following questions should be asked when assessing the likelihood of particulate contamination:

Outside inspection

• Is the ‘boot supply’ (where unconditioned air is entering the system) sealed properly where it is installed to the exterior of the building
• Are the outside air dampers screened, and is the entry free of debris and dirt? Is there dust on surfaces?
• Is the filtering system designed for primary filters, rated between 10% and 30% dust-spot efficiency, and for secondary filters, rated between 40% and 85% dust-spot efficiency?
• Are filters installed and maintained properly?
• Are particulates entering the air from the humidification equipment (spray or ultrasonic humidifiers, chemical disinfectants, corrosion, rust)?
• Are there chalky marks or cement-like odours around the humidifier?

Indoor inspection

• Are there personal ultrasonic humidifiers in the workplace?
• Is there evidence of damaged insulation in the ducts or AHUs (air handling units)?
• Are there dirt marks or white dust on diffusers, indicating particulates entering from the ventilation system?
• Is smoking taking place anywhere in the building?

Assess the Air Quality

Understand what the concentration of particles is in the air.  Actions such as below.

• How much black carbon/diesel particulate is in the air in the office?
• What is the concentration of particles of different size ranges is in the air (PM1, 2.5, 4, 10)?
• Understand the range of sizes of particles in the air
• Know what the concentration of particulate is in the supply air ducts and the return ducts

From this data the office air quality can be determined as well as the efficiency of the air conditioning system to remove air pollution from the air supply.  K2 Environmental is able to help with all of the above actions.

Advised Actions

• Replace filters in the air conditioning vents more regularly
• Use additional extraction/ventilation to reduce the amount of particles in the air
• Insulate air ducts to reduce condensation
• Clean and maintain air conditioning unit regularly
• Use a dehumidifier to decrease the chance of mould
• Ensure indoor sources of particulate are reduced by moving supply vent outdoors

Contact K2 Environmental today for your air quality assessment