How I Learned to Respect the HSNO Classification System And Why It’s Critical for Health and Safety

There’s a certain moment in every health and safety professional’s journey when you realize your biggest risks may not be the loudest machines or highest platforms but the quiet chemicals sitting in the corner of a storeroom.

For me, that moment came during an unplanned walkthrough. I spotted a spray bottle labelled “Cleaner A.” No HSNO class, no GHS pictogram, no PPE nearby. I asked the team what it was, and someone said, “It’s fine, we’ve used it for years.”

I dug into the Safety Data Sheet (SDS). Turns out, “Cleaner A” was classified as:

1. HSNO 3.1C – Flammable liquid (flash point between 23–60°C)

2. HSNO 6.1D – Harmful if swallowed or inhaled

3. HSNO 6.3A – Causes skin irritation

4. HSNO 9.1C – Harmful to aquatic life

   
   

And it was being used with no ventilation, stored next to a degreaser classified as HSNO 5.1.1C – an oxidizing liquid. That’s not just unsafe it’s non-compliant.

That’s the day I realized: if I don’t understand HSNO, I don’t understand the real risks in my workplace.

What Is the HSNO Classification System?

The Hazardous Substances and New Organisms (HSNO) Act classification system is how New Zealand categorizes and controls substances that pose physical, health, or environmental risks.

The system breaks substances into classes (1 to 9) and subclasses, based on the type and severity of hazard. Unlike a general SDS hazard pictogram, HSNO

Classifications tell you:

• How a substance behaves

• How dangerous it is (e.g. fatal vs. harmful)

• How to legally manage, store, label, and use it

  
  

For example:

• Class 3.1B: Flammable liquid, flash point below 23°C

• Class 6.1A: Acutely toxic can cause death from small exposure

• Class 8.2C: Causes skin burns

• Class 9.1A: Very ecotoxic to aquatic life

  
  

These numbers are not optional. If you hold hazardous substances above certain thresholds, they trigger mandatory controls under the Health and Safety at Work (Hazardous Substances) Regulations 2017.

Where I Started: Building an HSNO-Based Inventory

I began my transition by converting our existing chemical list into an HSNO-classified inventory. This meant:

• Listing every product's HSNO class and subclass

• Recording UN number, quantity, and location

• Cross-referencing thresholds using EPA’s Hazardous Substances Calculator

  
  

One big surprise? Several substances we thought were “low risk” were triggering requirements for location compliance certificates. For instance:

• Over 50L of Class 3.1B (flammable liquids) inside a building requires certified fire-resistant storage

• Over 100L of Class 6.1D (toxic) triggers emergency planning and signage

• Over 1000L of Class 9.1D (eco-toxic) requires a hazardous atmosphere zone assessment

  
  

Applying It: Real-World Examples and Lessons

Here are three ways HSNO classifications changed our approach:

1. Storage Compatibility

Before HSNO, we grouped products by department. After classification, we regrouped based on hazard class compatibility:

• Class 3 flammables were stored away from Class 5 oxidizers

• Class 6.1 toxic substances were separated from food production areas

• Class 8 corrosives were placed on spill trays, in bunded shelves with secondary containment

  
  

We used the NZS 5433:2020 Dangerous Goods Segregation Chart to redesign the entire chemical storage layout.

2. Labelling and Decanting

Most decanted chemicals had no HSNO labelling. Now, we implemented:

• GHS-aligned labels with HSNO class, hazard statements, and pictograms

• Clear rules: No decanting without pre-labelled containers

• Training for team members to read a classification code and know what PPE is required

  
  

3. Training and Emergency Planning

We customized our site induction to include:

• How to read HSNO codes on chemical labels

• What PPE is required based on class (e.g. 8.3A requires full face protection)

• What to do during a spill, and how different classes behave (e.g. Class 5.1.1C oxidizers can intensify fires)

  
  

We also ran HSNO-specific drills, like:

• Containing a Class 3.1C flammable spill near a heat source

• Cleaning up a Class 8.2B corrosive substance on skin

  
  

The Cultural Shift

What surprised me most wasn’t just the technical benefits. It was how people changed the way they talked about chemicals.

Workers started saying things like:

• “That one’s a 6.1C, let’s move it away from the lunchroom.”

• “This is over the 250L limit for Class 3 do we need signage?”

  
  

That’s when I knew: HSNO had moved from paperwork to practice.

Final Thoughts: This System Makes You Sharper

As a safety leader, my job is to protect people from the risks they can't always see. The HSNO classification system is what finally gave me the language, structure, and confidence to manage chemical risk properly.

You don’t need to memorize every class and subclass. You just need to start using them:

• Look them up

• Apply the thresholds

• Adjust your storage, training, and signage accordingly

  
  

Because when it comes to health and safety, you can’t manage what you don’t understand and HSNO is how we start to understand.

📩 Want help reviewing your chemical inventory or ensuring you’re compliant with HSNO thresholds and controls? I offer practical support for audits, training, and real-world implementation.

Let’s work smarter and safer.