Here is a common and understandable mistake. A lab buys a ductless fume cupboard, fits a general purpose carbon filter, and assumes it will handle whatever gets used at the bench. Most of the time it does. But carbon is not a universal sponge, and a few important substances slip straight through untreated carbon as if it were not there.
Getting the grade right is the single most important decision you make with a recirculating cupboard, because the filter is the thing standing between the fumes and the person breathing nearby. The good news is that it is not complicated once you understand the basic idea.
Why one carbon does not fit all
Activated carbon works by adsorption. Vapour molecules stick to the enormous internal surface area of the carbon as air passes through. This works very well for solvents and most organic vapours, which is why a general purpose grade covers a great deal of everyday laboratory work.
The problem is that some substances, particularly small, light molecules such as ammonia and formaldehyde, are not held well by plain carbon. To capture those, the carbon is treated, or impregnated, with a chemical that reacts with the specific vapour and locks it in. A formaldehyde grade and an ammonia grade are not marketing labels, they are genuinely different media doing a different job.
The filter should be chosen for the substances in use, never by odour alone. Some of the most hazardous vapours have little or no smell.
The main grades, in plain terms
Most laboratory work is covered by a handful of grades. Here is the general idea behind each, though the right one for you always depends on the specific chemicals and quantities.
| Grade | Broadly suited to |
|---|---|
| GP General purpose | The most widely used grade. Solvents, alcohols, hydrocarbons, and a broad range of organic vapours. |
| FOR Aldehyde | Formaldehyde and glutaraldehyde. Common in histopathology and specimen work. |
| ACI Acid | Acidic vapours such as halogen and mineral acids. |
| AMM Ammonia | Ammonia and amines. |
| GRD Education | A combined grade developed for the mixed chemistry of teaching laboratories. |
| HEPA | Powders and particulates rather than vapours. |
| Custom | A blend where more than one chemistry is in use. |
There are also specialist grades for trickier chemistry, such as mercury or hydrogen sulphide. These are the exception rather than the rule, but they exist for good reason, and it is worth asking if your work involves anything unusual.
Before you order, know these three things
- The substances you use, by name where possible, not just the general type of work.
- Roughly how much, and how often. A filter has a finite capacity, and heavy use shortens its life.
- The cabinet make, model or filter size, so the replacement physically fits.
What about particulates?
If your concern is fine powder or dust rather than vapour, carbon is not the answer at all. A HEPA filter captures particulates, and where you have both powder and solvent in play, a combined carbon and HEPA arrangement handles the two together. Weighing and handling fine powders is a good example of where this matters.
When filtration is not enough
It is worth repeating the honest caveat. Filtered cupboards suit most laboratory work, but not where very large quantities are produced, such as evaporating solvents to dryness, nor for very highly toxic substances or unknown reactions. If your work falls into that territory, the conversation should be about a ducted system, not which filter to buy.
Fumecare filters, for any make of cabinet
We manufacture carbon, HEPA and custom-blended filters to fit our own and other manufacturers' cabinets.