Source Capture vs. Conventional or General Ventilation
Source capture for point source emissions is the method of choice for protecting both the workers’ breathing zones and the general working environment. Moreover, source capture is the method required by the CSST.
In fact, this type of ventilation is their first requirement for point source emissions.
It’s important to understand that general ventilation dilutes air pollutants but does not eliminate them. As for conventional ventilation, it requires significant airflow rates.
The primary objective of factory ventilation is to reduce the concentration of contaminants below acceptable permissible exposure values (PEVs). To do so, we can choose between three primary forms of ventilation, described below.
This ventilation method mixes fresh outdoor air with the contaminated air to reach a pollutant concentration level that falls below PEVs. The quantity of fresh air that enters the factory must be adjusted based on the contaminant’s emission rate.
Let’s consider the example of a factory worker at a welding station, with only general ventilation as protection against exposure to welding fumes. With general ventilation, preheated fresh air is distributed in the factory through diffusers covering the entire work area, which ensure that enough fresh air is distributed throughout the factory. The fresh air supply mixes with the factory air, which contains the welding fumes. Before the welding fumes can be diluted by the fresh air, however, they will surround the worker. With only general ventilation, factory workers’ breathing zones cannot be protected against potential overexposure. It is therefore very likely that our welder will be exposed to concentrations well above PEVs.
Moreover, the cost of replacing fresh air will be staggering and many workers’ degrees of exposure may exceed PEVs. In such a case, the CSST could notify the factory that their ventilation method does not meet the required standards.
Air that has passed through a dust extractor can be recirculated, but it cannot be used in the calculation of fresh air needed for an air change.
Source capture with high-speed, low-volume technology is a more affordable method in the medium and long term.
With general ventilation, new investments may be necessary to meet the required standards. Why not choose the right solution the first time around ?
Conventional ventilation can be used to perform source capture. However, this method uses very high airflow rates, and the collection devices are large and cumbersome. It would be impossible to reduce the dimensions of these collection devices because within the network of such systems, no energy is available.
Their high airflow rate and low operating pressure require the use of large-scale ducts, which are often difficult to install due to the amount of space required. Conventional ventilation also involves fresh air supply systems with significant airflow levels that work to balance air pressure in the factory. This results in significant operational costs.
If we decide to recirculate some of the expelled air to reduce the cost of heating make-up air, very large dust extractors are also required. This type of equipment is expensive, both to purchase and to operate, because it requires a great deal of maintenance, including the periodic replacement of cartridges. It is also important to remember that the filtered and recirculated air cannot be used in the calculation of the factory’s hourly air changes. Air used to calculate the hourly air changes must be fresh outdoor air that has been heated. This is what leads to the technology’s significant operational costs. However, unlike general ventilation, workers have a protected breathing zone as the pollutant is contained at the source.
Source capture with high-speed, low-volume technology is a more affordable method in the medium and long term. It requires fewer air changes per hour when compared to general and conventional ventilation because of its low airflow extraction. Moreover, it ensures that the employee breathing zone is protected.
When using this method, factory air is nearly exempt of pollution and is well below PEVs, unlike general ventilation. This is because source capture almost entirely eliminates the pollutant before it can be dispersed in the factory.
The expelled airflow is so low compared to other technologies that, in many cases, dust extractors are not necessary to recirculate all or part of the air. However, with source capture, there is no return on investment because airflow rates are too low. Furthermore, a minimum number of air changes per hour is required. It is important to note that the minimum number of air changes per hour can vary according to your factory’s activities. Additionally, to eliminate contaminants in the air before expelling it outside, the dust extractor required is very small because the high-speed, low-volume technology reduces the airflow supply by 90% compared to conventional ventilation. Lastly, the CSST’s first regulation on point source emissions is respected.
In short, high-speed, low-volume technology is:
- The most efficient
- The most affordable to operate
- Tompletely in line with CSST requirements
- It requires the least amount of air changes per hour
- It meets the PEV requirements for workers’ breathing zones