Ep.30: Spontaneously Combustible Substances: The Fire Risk You Didn't See Coming

Some chemicals don’t need a flame to catch fire — just exposure to air. 

In this episode, Patrick Gee unpacks the hidden dangers of Class 4.2 spontaneously combustible substances — and what it takes to store and handle them safely. 

You’ll learn: 

• The difference between pyrophoric and self-heating substances 
• How Packing Groups classify danger levels 
• The strict cabinet requirements under AS/NZS 5026 
• What signage and ventilation systems are legally required 
• Why training and risk assessments are non-negotiable 

Whether it’s white phosphorus or aluminium alkyls, this episode breaks down how to control one of the most underestimated fire risks in the workplace. 

🎧 Subscribe now to keep your dangerous goods knowledge sharp and your team safe. 

Transcript

Introduction to Spontaneously Combustible Substances

Speaker 1 0:06

Hello and welcome to Chemical Safety at Work , the podcast that helps you better understand dangerous goods and the steps you can take to keep your workplace safe and compliant . I'm your host , patrick G , and today we're talking about a particularly dangerous and often misunderstood group of chemicals spontaneously combustible substances . Now , if you're working with materials like white phosphorus or aluminium alkyls , this episode is especially important . These substances can actually ignite on their own just from being exposed to air . Let's dive into what makes these chemicals so dangerous , how they're classified and how to safely store and handle them in your workplace . So what exactly is a spontaneously combustible substance ? As the name suggests , these chemicals can self-ignite when they come into contact with oxygen , sometimes in just a matter of minutes . These substances fall under class 4.2 of the Australian Dangerous Goods Code , that's the division specifically for substances liable to spontaneous combustion . Class 4 is split into three divisions Division 4.1 , flammable solids , division 4.2 , spontaneously combustible substances , and Division 4.3 , dangerous when wet . Today we've focused on Division 4.2 , and there are two key categories here Pyrophoric substances , which ignite within 5 minutes of air exposure , and self-heating substances ,

Understanding Class 4.2 Classifications

Speaker 1 1:40

which catch fire slowly over hours or days , especially in large quantities . These substances can be incredibly dangerous if not handled correctly . We're talking about human harm from exposure , fire and explosion risks , toxic gases released during a fire , contamination of air , land and water , reactions with incompatible chemicals and , of course , major property damage . And because of these risks , class 4.2 substances are assigned a packing group which tells you how dangerous the chemical is . There are three levels Packing group 1 , high danger . Packing group 2 , medium danger and packing group three , low danger . For example , pyrophoric solids and liquids are packing group one . Meanwhile , self-heating organic substances might fall into packing group two or three , depending on the level of risk . You'll find the packing group in the safety data sheet , so always check the STDS before working with any new substance .

Speaker 1 2:46

Storage is absolutely critical when it comes to spontaneously combustible substances . The Australian standard ANNZS 5026 outlines what's required when storing class 4 dangerous goods . Let's run through the main options goods . Let's run through the main options A freestanding , roofed chemical store , a room attached to an external wall , a specially designed area inside a building with a fire resistant wall or , where appropriate , an open air storage facility and , of course , a compliant , fire resistant chemical storage cabinet .

Speaker 1 3:27

If you're using a cabinet and many workplaces do it needs to meet very specific requirements . It must be made from double walled steel . The internal space within the walls needs an air gap

Safe Storage Requirements

Speaker 1 3:40

of at least 40 millimeters . The bottom must contain any leaks , at least 150mm deep and liquid . Tight Shelves should be perforated to allow air movement . Doors must be self-closing and held shut by a friction or magnetic mechanism that'll release under pressure and , importantly , components must not melt under 850 degrees Celsius . All of this is designed to give you time to react if something goes wrong and to prevent a small issue from becoming a disaster . Storage cabinets must also include clear signage . Here's what you'll need A class 4.2 , spontaneously combustible label at leastimetres long , no smoking , no ignition sources within three millimetres .

Speaker 1 4:29

In letters , at least 50 millimetres high , the cabinet's maximum capacity and the name and address of the manufacturer . Now let's talk ventilation . If there's any chance of your stored substances releasing toxic or flammable vapours , mechanical ventilation is a must . That means ducting designed to prevent back pressure , and it must direct fumes away from ignition sources and anywhere where people might gather . Speaking of ignition , this one's simple but essential there must be no ignition sources within three meters of your class 4.2 cabinet . That includes sparks from equipment , hot surfaces , static discharge , even someone lighting a cigarette on their break . Make sure your team understands this and make sure they've been trained to recognize these risks .

Speaker 1 5:23

All of this storage signage exclusions . It only works if your people understand what they're dealing with .

Proper Signage and Ventilation

Speaker 1 5:30

All staff and contractors must be trained in how to safely store and handle class 4 substances and how to identify and eliminate hazards . Don't forget to carry out a risk assessment of your site . That's your roadmap for making sure every hazard is accounted for and controlled . So to wrap it up , spontaneously , combustible substances class 4.2 , are extremely dangerous , but with the right systems in place , they can be stored and handled safely . Always check your SDS , choose the correct storage solution , mark your cabinets clearly , train your team and keep ignition sources well away .

Speaker 1 6:13

Thanks for tuning into Chemical Safety at Work . If you found this week's episode helpful , please subscribe to Chemical Safety at Work on your favorite podcast platform and rate or leave us a review . We'd love to hear from all of our listeners , so send us a message and let us know if there are any topics

Training and Risk Assessment

Speaker 1 6:30

you'd like us to do a deep dive on . Until next time , stay safe , stay compliant and always respect the risk . Until next time , stay safe , stay compliant and always respect the risk . Until next time , stay safe , stay compliant and always respect the risk . Until next time , stay safe , stay compliant and always respect the risk .