The ultimate guide to chemical storage ventilation
13 January 2022
Flammable substances and liquids are used in most laboratory, academic, pharmaceutical and industrial environments, but storage of these materials improperly can pose a great risk. Read More.
Your site may have a set quality system that you can access, which will explain the guidelines and processes specific to the materials and liquids that you may be in contact with daily, but in this article we address the basic idea behind effective chemical storage room ventilation.
What are chemical storage units
Chemical stores are exactly as they sound, they are used within the previously mentioned sectors to store potentially hazardous chemicals that are used in the daily activities of those working there. There are a large variety of chemical storage cabinets available on the market, but best practice guidelines for the control of substances hazardous to health (COSSH) chemical storage units, indicate that a chemical store or the direct area around it, should be well ventilated. Those available on the market include both ventilated and non-ventilated units. When deciding what you need it’s useful to understand the importance of effective chemical store ventilation to determine the type of chemical storage unit that would be best suited to your particular requirements.
The importance of ventilated storage units
When choosing a storage unit for the safekeeping of flammable substances, ventilation should be one of the key points to consider, and if not purchased as a full encompassed ventilated unit where there is no need for outside extraction and filters are used, it is advisable to fit industrial chemical fans suitable for the purpose of ventilating the store. Proper room ventilation with adequate air changes will eliminate most unsafe chemical vapours. Therefore, if the room in which the chemical store is not adequately ventilated on its own, then the chemical store itself should definitely be ventilated.
The need for ventilation and more specifically the type of fan that is required is determined by the hazardous nature of each chemical component as temperature fluctuations in many chemicals can serve to increase vapour emissions and flammability so the need for ventilation becomes ever more apparent, especially when a unit is situated in direct sunlight. Effective ventilation not only keeps chemicals appropriately cooled but also reduces this build-up of fumes.
As a general rule, any ventilation system should exhaust fume continuously outside into the atmosphere and away from additional sources of ignition. By exhausting away, this prevents surrounding rooms and people from inhaling or being affected by the harmful gases. Domestic fans do not meet this criteria and should not be used.
Chemical classifications and fan specifications
Chemicals can be classed in two categories, flammable and corrosive. Where corrosive chemicals are stored in a chemical storage cabinet, the mechanical fan should be constructed of corrosive resistant blades and shrouds and be capable of dispersing corrosive vapours, gases, or mists. The ventilation ducting should provide at least the same level of corrosion protection as the cabinet walls and be resistant to any vapours or fumes which may be exerted from the chemicals stored in the cabinet. ATEX certified industrial fans are designed specifically for use within potentially hazardous or combustible environments, those with flammable gases presents, and are manufactured with non-sparking components such as copper inlets to prevent explosions.
In smaller storage units where the materials are non-corrosive and ventilation is more general, an axial fan can be used to ventilate. This should be certified for use in ATEX applications but in these instances the motor that is held within the air stream can withstand the nature of the gases, fumes or mists. It is worth noting that flammable gases are denser than air so they can accumulate at floor level. For this reason the ventilation system should be set up to ensure that these low level potentially hazardous gases can be extracted effectively.
Flammable and corrosive fumes in chemical stores
Corrosive fumes, when in large volumes and over long periods will damage or destroy materials that they come into contact with. Substances containing corrosive gases, like those found in sulphuric or hydrochloric acids, will erode the surface of the fan components if not manufactured in suitable material fit for purpose. The extraction of corrosive fumes should be done with chemical fans otherwise known in the marketplace as corrosion resistant fans. Polypropylene is the standard plastic material used for corrosive atmospheres as it can withstand the nature of the chemical gases that pass through the scroll and the impellers. In this instance the motor should be kept out of the air stream to ensure long lifespan. It also prevents the overheating of any motorised components. As previously mentioned, the duct work that is attached to the industrial fan should also carry a similar level of protection against corrosion as the fan scroll and impeller. In many site specific specifications documents, it will advise that adequate mechanical ventilation must be provided and controlled from a switch located outside of the storage room door and that the chemical store exhaust should be at floor level since flammable vapours tend to sink in air as briefly advised earlier.
If corrosive fumes from an acid cabinet are a problem, the acid storage cabinet may be connected to the duct work of a fume hood. Standard PVC duct can be used. Keep the air flow to a bare minimum and eliminate as much of the horizontal run of the duct as possible. This will reduce condensation and precipitation of the acid vapours. Connecting the acid cabinet to the existing fume hood will dilute the concentration of the acid fumes and will not harm the exhaust hoods system since it is designed to handle corrosive fumes.
Chemical storage in academic laboratory settings
Chemical storage areas in academic laboratory settings include storerooms, storage cabinets, refrigerators, freezers, preparation areas, laboratory work areas and central departmental stockrooms. For the purposes of keeping to topic, this section does not cover fume extraction hoods that are commonplace within schools, universities and hospitals and focuses purely on the aspect of chemical storerooms only.
There are recommendations and guidelines around how to legally segregate incompatible chemicals from each other, in addition to additional storage requirements for specific hazardous chemical classes. In general, this includes isolating particularly flammable, reactive and toxic materials for additional safety and not storing chemicals within fume cupboards so as not to interfere with the air flow, but to store in separate cabinets that vent directly into the fume hood to enable the fumes to be exhausted safely. As school science preparation areas use several hundreds of chemicals, all with their own allowable exposure levels, and as schools will have no capacity to measure the levels that are present, the effective solution is to provide excellent extractive ventilation to minimise exposure to those working in the area.
Top educational establishments have a system that is tested and maintained alongside their fume extraction hoods with dedicated fan units and ducted ventilation from all the key points in the preparation room alongside the use of airflow monitors to check the air changes per hour. Standards and specifications will vary according to individual site guidelines so yours may be different.
Specifications advise that a mechanical exhaust ventilation system must be present and should provide at least seven air changes per hour (FDNY) and additional local exhaust ventilation may be required if activities such as dispersing takes place in the storage area. If the installed extraction fan is dirty this will mean the air quality is compromised so this should routinely be checked.
Signs that chemical storage ventilation may be inadequate
It is a recommendation that ventilation of both the preparation and storage areas is subject to a formal risk assessment process to check its effectiveness. Signs that the ventilation may be inadequate could include, but are not limited to, the below:
- Allergic reaction type responses from occupants in the room. This can include nausea, headaches, vomiting, irritation to the eyes or dizziness. If the flammable liquids stores inside the cabinet are listed in the workplace exposure standards and the concentration of the vapours exceed the legal limit, then the cabinet must be ventilated. The ventilation system will reduce the concentration of the flammable vapours which will also make the area feel safe for people to work in.
- Detectable odours upon entering the workspace. This could be a build-up of volatiles within the stores such as those for flammables or corrosives. This will be obvious when the door of a storage cabinet is open, and it indicates poor ventilation or bad housekeeping.
- Condensation build-up on the outside of storage buildings and on the walls of the chemical store. This usually applies to corrosives or flammable chemical stores.
- Degrading of labels due to condensation or corrosion
- Corrosion of fixtures and fittings such as rusting.
Features of well-designed chemical storage ventilation include:
- The mechanical ventilation system should be designed so that it prevents any odours escaping the room
- The ventilation system should be vented to the outside atmosphere in a location that is safe to disperse vapours. A safe place will be away from ignition sources and areas where people congregate.
- The air inlet should be attached to the vent port at the top of the cabinet and the vapours should be extracted from the bottom vent port using an exhaust fan. This configuration is most effective as the most dangerous vapours are heavier than air and reside at the bottom of the cabinet.
- Any ventilation system that is used to extract flammable vapours will need to have a safe ATEX exhaust fan to manage the corrosive or flammable fumes.
- A ventilation system cannot be linked to multiple cabinets as this can cause vapours from incompatible dangerous good to mix, resulting in explosive reactions.
- The ventilation duct must not be smaller than the size of the venting opening on the side of the cabinet.
Industrial fan solutions suitable for chemical storage ventilation
Specifying the right fan to suit an application can get confusing for an outsider, so to make it simple, there are two key pieces of information required; the airflow rate and the system resistance. Airflow rate is based on the number of air changes per hour needed in the storage area. From the airflow rate, the size the ductwork is determined and so the system resistance is calculated. There may be a requirement to control the fan with a sensor to switch the fan on and off. This can be achieved with the use of an inverter. The sensor sends a signal to the inverter, which in turn controls the power source to the fan. The supplier would also obviously need to understand the type of chemicals you’re working with, corrosive or flammable etc., so they can be sure that you’ll need a plastic fan over a stainless-steel equivalent.
Please note that if there is a possibility the installation needs to be ATEX rated, then an expert ATEX consultant needs to determine the Zone classification for the area. The information they provide will cover the size of the Zoned area and the standard of equipment to be used in the Zone.
About the author:
With over 10 years’ experience in corrosive and hazardous environments, Faye Brophy heads up the Industrial division at Axair Fans UK Limited.
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