If your organisation stores or uses any class 4 flammable solids such as carbon, sulphur, or phosphorus, it’s important to minimise risk to people, property and the environment by storing these hazardous goods in a safe and compliant manner. Flammable solids are prone to spontaneous combustion, and if they should come in contact with water, will emit flammable gasses susceptible to ignition.
Australian Standard AS/NZS 5026-2012 – The storage and handling of class 4 dangerous goods divides class 4 dangerous goods into three divisions and defines them as follows;
Division 4.1 – flammable solids, self-reactive substances and solid desensitized explosives
- Solids that, under the conditions of transport, are readily combustible, or may cause or contribute to fire through friction. Self-reactive substances that are liable to undergo a strongly exothermic reaction. Solid desensitized explosives that may explode if not sufficiently diluted.
Division 4.2 – substances liable to spontaneous combustion
- Pyrophoric substances: These include solutions and mixtures (liquid or solid) that, even in small quantities, ignite within 5 minutes of coming in contact with air. These are the division 4.2 substances most liable to spontaneous combustion.
- Self-heating substances: These substances (other than pyrophoric substances) are liable to self-heating. They will ignite only when in large amounts (kg) and after long periods of time (hours or days).
Division 4.3 – substances that, on contact with water, emit flammable gases
'Dangerous when wet’ substances which, in contact with water, can emit flammable gases that can form explosive mixture with air. Such mixtures are easily ignited by all ordinary ignition sources, e.g. naked lights, sparking hand tools, or unprotected light bulbs. The resulting blast wave and flames may endanger people and the environment.
NOTE: emitted gases may also be toxic.
As per the description above, class 4 dangerous and hazardous goods are prone to react, and result in fire. It is important that class 4 dangerous goods are kept away from any potential ignition source, and stored in such a way as to prevent combustion. Should a fire occur, it must be noted that poisonous, suffocating gasses may be produced. It’s your choice to make. Store your dangerous goods correctly, and minimise the risk associated with class 4 substances to the people, property and environment around your workplace.
Ventilation requirements according to AS/NZS 5026
The Australian standard that outlines the ventilation requirements for flammable solids is AS/NZS 5026 – The storage and handling of flammable and combustible liquids.
Section 5.7.5 of AS/NZS 5026:2012:
5.7.5 Ventilation of cabinets
Where ventilation is installed the design of any vent opening in the cabinet wall shall not compromise the structural strength of the cabinet.
Where a toxic or flammable gas could be emitted, ducting shall be designed in such a manner as to prevent back-pressure and shall be directed away from ignition sources and areas where people congregate.
NOTE: ventilation provision should be designed by an appropriately qualified person.
As this section does not state that ventilation ‘shall’ be installed on the cabinet, it means that ventilation is not a mandatory requirement. However, section 6 of AS/NZS 5026:2012 outlines design requirements for cabinets storing division 4.1 flammable solids and states that “each cabinet or compartment shall be ventilated.”
Therefore, if you were storing 4.1 flammable solids, the dangerous goods storage cabinet must be ventilated as per details set out in AS/NZS 5026.
If you are storing division 4.2 or division 4.3 dangerous goods, ventilation is not mandatory unless the particular substance that you are storing is listed in the workplace exposure standards, and above the maximum concentration limit.
Workplace exposure standards
Exposure to any kind of hazardous substances will prose significant health risks upon your workers. Some of these health risks include
- Irritation to the eyes, ear and throat
To help combat these health risks, Safework Australia developed the workplace exposure standards. These exposure standards identify around 700 hazardous substances and their legal airborne concentration limits.
If the product that you are storing is classified as either class 4.2 or 4.3 flammable solids and listed in the workplace exposure standards, and the concentration of the vapours exceed the limit outlined in this standard, the flammable solids storage cabinet will require ventilation. If you are unsure, it’s always best to check with a specialist.
Features of a compliant ventilation system for toxic substances
If you conduct a dangerous goods risk assessment and determine that your flammable solids storage cabinets require a ventilation system, it is important that the ventilation system is installed in such a way that it doesn’t pose any further risks to the people of your organisation. A safe ventilation system must follow the requirements outlined below:
- A mechanical ventilation system of a class 4 storage unit should be designed so that it prevents any vapours from escaping into the room.
- The ventilation system of a class 4 storage unit shall be vented to the outside atmosphere in a location that is safe to disperse vapours. A safe location will be away from ignition sources and places where people congregate.
- The air inlet shall be attached to the vent port at the top of the cabinet and the vapours shall be extracted from the bottom vent port using an exhaust fan. This configuration is most effective as most flammable vapours are heavier than air and reside in the bottom of the cabinet.
- Any ventilation system that is used to extract flammable vapours will need to have an intrinsically safe exhaust fan.
- A ventilation system cannot be linked to multiple cabinets. This can cause incompatible vapours to mix, resulting in violent reactions.
- When a mechanical ventilation system is not attached to a cabinet, the vent bungs must be tightly screwed into the vent ports. This stops any flammable vapours from escaping into the workplace.
- In all instances the ventilation system shall not compromise the structural integrity of the cabinet.
- In all cases the ventilation duct shall not be smaller than the size of the venting opening on the side of the cabinet.
- A class 4 dangerous goods ventilation system shall be designed by an appropriately qualified engineer and it shall comply with AS/NZS -1668.2-2002
As flammable substances are very susceptible to reaction, particularly combustion, it is very important that class 4 dangerous goods storage cabinets are ventilated appropriately and compliantly according to Australian standard AS/NZS – 1668.2-2002.
For more detained information and specifications on how to ventilate dangerous goods storage cabinets, download our free eBook by clicking on the image below.