Passive fire protection is the part of a building that slows fire without anyone pressing a button. Fire-resistant walls, floors and boards split the building into sections, and seals close the holes where cables, pipes and ducts pass through. Open holes give flame and smoke a shortcut. FlameBlock Mineral Wool and Shield are made to close them.
Key insights
- Passive versus active: active protection (extinguishers, sprinklers, alarms) has to detect a fire or be used by someone. Passive protection is built in and works whether anyone is there or not.
- The minutes matter: Fire Ops SA CEO De Wet Engelbrecht says the first 15 to 20 minutes “can determine whether a fire is contained or spreads into other parts of the home, including the roof” (Fire Ops SA and Discovery Insure release, 8 September 2026).
- Battery fires test the building: after a container battery fire in Roodepoort in January 2026, crews stayed on site for about 24 hours (Green Building Africa, 9 September 2026).
- One insurer’s advice on battery stock: TT Club, a transport and logistics insurer, advises a dedicated battery storage area, or better a separate warehouse, built with fire-resistant materials (Insurance Edge, 25 September 2026).
- Two FlameBlock products, one job: Mineral Wool fills and lines, Shield seals over it.
What is passive fire protection?
Think of a ship with watertight compartments. One section floods, the doors close, the ship stays up. Buildings use the same idea for fire, and it’s called compartmentation: the building is split into sections by walls and floors that resist fire for a set time, so a fire in one room stays there long enough for people to get out and for firefighters to arrive.
That’s passive fire protection. Fire-rated walls and doors, boards around steel, sealed service openings. None of it needs power or a person to switch it on.
Active protection is the other half: detectors, sprinklers and the extinguisher on the wall. You need both. Active systems depend on something working on the day. Passive protection is already in place.
In South Africa, Part T of the National Building Regulations deals with fire protection, and SANS 10400-T sets out how to meet it. Which walls need what rating depends on the building and how it’s used, so that call belongs to your architect, fire engineer or another competent person.
Why do the gaps matter more than the wall?
Because fire looks for the easy way through. A fire-rated wall can be built perfectly and then drilled. A cable goes through to the plant room. Later someone adds an aircon pipe out to the condenser, and a data cable for the new camera. Each hole is a route for flame, hot gas and smoke into the next room or up into the roof space.
Most buildings that have had a backup system added recently have new holes. Solar and battery installs run cables from the roof to the inverter, from the inverter to the distribution board, sometimes through walls that were meant to hold back a fire. The installer is there for the electrical work, so ask who seals the holes afterwards, and with what.
Ordinary expanding foam doesn’t count. Unless it’s a fire-rated product, it fills the gap without resisting fire.
How do you firestop a gap around cables and pipes?
You fill it with something that won’t burn, then seal the surface so flame and smoke can’t push through. The trade calls this fire stopping, and a sealed opening around a cable or pipe is called a penetration seal. FlameBlock’s two products split the work.
FlameBlock Mineral Wool is a high-density, non-combustible board (it doesn’t burn). FlameBlock describes three jobs for it: thermal insulation, acoustic dampening and fire resistance. It’s used around energy storage, industrial machinery, HVAC enclosures (heating, ventilation and air conditioning) and passive firewalls, the walls built to hold a fire in one part of a building.
FlameBlock Shield is a mastic paint paste, thick enough to work into a joint, that FlameBlock formulated to work with rock wool. Rock wool is a type of mineral wool spun from molten rock. Applied around cables, pipes and ducts where they pass through a wall or floor, it creates a fire barrier that FlameBlock says helps stop flame and smoke spreading between compartments.
Used together, the wool fills the opening and Shield seals it. The cables still run, and the gap stops being a shortcut.
Where does passive protection matter most?
Anywhere a fire would do the most damage or spread the fastest:
- Battery and inverter rooms. The Roodepoort fire kept crews busy for a day. A battery room with sealed walls gives everyone more room to work. Read why an ordinary extinguisher may not be enough for a battery fire.
- Plant rooms, server rooms and electrical risers, where cables run in bundles through walls and floors.
- Warehouses holding lithium-ion stock, given TT Club’s advice on fire-resistant storage areas.
- Shared walls and ceilings in complexes and office parks. A gap above a ceiling can carry a fire next door.
- Homes with solar, wherever cables pass from the garage or outbuilding into the house or roof.
A walk-round checklist for facility managers
You don’t need special tools for a first look. A torch and a ladder will do.
- Lift a ceiling tile next to the plant room or server room. Does the wall stop at the ceiling, or does it run all the way up?
- Look at every place a cable bundle goes through a wall. Is the hole sealed, or can you see light around it?
- Check where the aircon pipes leave the building.
- Follow the solar cables from the roof to the inverter and the distribution board, and note each wall they cross.
- Write down what you find, with photos, and get a fire professional to look at the list.
Frequently asked questions
Is passive fire protection only for big buildings?
No. Any home with a battery in the garage or cables through a wall has the same gaps, just fewer of them.
What’s the difference between mineral wool and rock wool?
Mineral wool is the family name. Rock wool is one type, made from rock. FlameBlock Shield is formulated to work with rock wool.
Does sealing the gaps replace extinguishers and alarms?
No. Passive protection holds the fire back. Active protection finds it and fights it. You want both.
How does fire spread through walls and ceilings?
Through the gaps around cables, pipes and ducts that pass through fire-rated walls and floors, often holes added later for aircon pipes, data cables or solar wiring.
Can I seal a gap with expanding foam?
Only if it is a fire-rated product. Ordinary expanding foam fills the gap without resisting fire.
The bottom line
Most fire safety talk is about what to do once a fire has started. Passive protection is the work done long before, in walls nobody looks at. Find the gaps and seal them properly, and a fire that starts in one room has a much harder time reaching the next. For the battery itself, see FlameBlock Lithium Black. Not sure what a room needs? Describe it to FlameBlock and they will suggest where to start.
Editorial note: this article is general guidance, not a fire design or compliance assessment. Product descriptions are FlameBlock’s own. Fire ratings and building requirements depend on your building, so confirm them with a fire professional.
FIND THE GAPS BEFORE A FIRE DOES
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