GRP Riser Decking, Protected Shafts and Fire Compartmentation

Why the compartment line — not a material-only debate — determines fire safety

GRP riser decking is widely used to provide permanent fall prevention and safe access within vertical service risers.

It is lightweight, anti-slip, corrosion resistant and can be configured around complex building services. Those practical advantages are important. However, the decision to use GRP in a riser should never be made on practical benefits alone.

It must be assessed against the building’s fire strategy.

The key question is not simply whether a deck is made from GRP or steel.

The key question is:

Does the completed riser maintain the required fire-resisting compartment line, including the shaft enclosure, openings, service penetrations, fire-stopping and smoke-control provisions?

That is the correct technical basis for evaluating any permanent riser-deck solution.

Start by identifying the compartment boundary

A service riser can pass vertically through a number of compartment floors. Each floor opening would otherwise create a potential route for fire and smoke to spread between storeys.

The solution is not to assume that an access deck itself becomes a compartment floor.

The solution is to form a protected shaft around the opening.

In a correctly designed protected service shaft, the compartment boundary is continued vertically by the construction enclosing the shaft. In practical terms, the fire-resisting line runs through:

• the compartment floor up to the riser opening;

• the fire-resisting walls enclosing the shaft;

• compliant protected openings, doors and access hatches;

• correctly detailed interfaces between construction elements; and

• tested fire-stopping around pipes, cables, ducts and other penetrations.

This is the compartment line.

The GRP deck sits within the protected shaft volume. It is not intended to be the fire-resisting barrier between storeys, and it should not be specified, represented or relied upon as one.

That distinction must be clear on the fire strategy, coordinated design drawings, product submittals and as-built information.

What a GRP riser deck does — and does not do

A permanent GRP riser deck has two principal functions:

1. Fall prevention around an open vertical riser.

2. Safe access for construction, commissioning, inspection and future maintenance.

It does not replace:

• a compartment floor;

• a fire-resisting shaft wall;

• a fire door or access hatch;

• a smoke barrier;

• a tested fire-stopping system; or

• the project’s passive fire-protection strategy.

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That is why it is technically incorrect to argue that changing an open GRP deck to an open steel deck automatically improves fire compartmentation.

A steel grid is not automatically a fire-resisting floor simply because it is metallic. Unless a construction has been specifically designed, tested and detailed to provide the required fire resistance, it remains an access or fall-prevention component.

The fire safety of the riser depends on the complete shaft arrangement, not on a single material selected in isolation.

Three different fire issues must not be confused

The debate around GRP riser decking often becomes confused because three separate disciplines are treated as though they are the same.

1. Reaction to fire

Reaction to fire concerns how a product may contribute to a fire under defined test conditions. Under the current European classification system, this is assessed through classifications under BS EN 13501-1.

2. Fire resistance

Fire resistance concerns whether a construction element can maintain its required performance for a stated period during a fire. Depending on the element, this can include:

• loadbearing capacity;

• integrity against flames and hot gases; and

• insulation against heat transfer.

This is a system-performance issue.

A riser deck should not be assumed to provide fire resistance unless it has been specifically designed, tested and evidenced for that function.

3. Compartmentation

Compartmentation is the continuity of the fire-resisting separation between parts of a building.

It depends on the walls, floors, interfaces, doors, hatches, penetrations, fire-stopping and installation quality that make up the compartment line.

A GRP deck can sit within a protected shaft without forming part of the compartment boundary. However, it must not compromise that boundary through poor support details, unsealed interfaces, obstructed inspection, inappropriate openings or interference with smoke-control and ventilation provisions.

Does permanent GRP decking automatically become a shaft lining?

No blanket conclusion can be drawn simply because a deck is permanent.

The guidance on internal linings is principally concerned with exposed linings to walls and ceilings. It also expressly excludes the upper surfaces of floors and stairs from that section of guidance.

That does not mean every deck is automatically outside all fire considerations. It means the question cannot be resolved through a simplistic statement that any retained deck inside a shaft is automatically equivalent to a wall or ceiling lining.

The correct assessment is project-specific and should consider:

• the shaft’s purpose;

• the location of the compartment line;

• whether the deck is within, or forms part of, the enclosing construction;

• the deck’s exposed surfaces and geometry;

• its relationship with ventilation and smoke-control systems;

• support and fixing details;

• the fire performance of the exact product proposed; and

• the requirements of the project fire strategy.

The permanent nature of the deck means it must be designed, documented and handed over properly. It does not, by itself, make it a fire-resisting compartment floor or prove that it is prohibited.

The conditions for a defensible GRP riser-deck solution

GRP riser decking should only be specified where the following points are satisfied.

The shaft is correctly identified

The design team must establish whether the riser is a protected service shaft and whether it has any additional role, such as part of a protected escape route, firefighting shaft, smoke shaft, gas-service route or specialist ventilation system.

A GRP deck must not be assumed suitable without explicit review where the shaft has an escape, firefighting, smoke-control, gas-ventilation or other specialist fire-safety function.

The compartment line is clear

The fire strategy and coordinated drawings should show that the fire-resisting shaft enclosure, rather than the deck, forms the barrier between the compartments connected by the shaft.

The deck does not compromise the enclosure

The deck, frame, support angles, brackets, fixings and interfaces must not:

• reduce the fire resistance of shaft walls or floors;

• create an unprotected route around the shaft enclosure;

• interfere with tested fire-stopping;

• obscure inspection of fire-stopping and services;

• bridge or load elements in a way not allowed by the fire-resisting construction;

• prevent required smoke ventilation; or

• obstruct essential service access and maintenance.

  
  

The product evidence is specific

A generic statement that “GRP is fire retardant” is not enough.

Evidence should relate to the exact deck proposed, including the relevant resin system, grating or slab profile, thickness, panel construction, support arrangement and intended end-use configuration.

Where a reaction-to-fire classification is required, the relevant evidence should be based on the current BS EN 13501-1 route and should be applicable to the intended installation.

Phenolic GRP and US Coast Guard evidence

For projects with enhanced fire-performance requirements, phenolic-resin GRP decking may be appropriate where supported by product-specific evidence.

Certain phenolic FRP grating systems are independently tested to ASTM F3059 for defined marine and offshore applications and can be accepted within the US Coast Guard framework for authorised locations.

This is valuable supporting evidence because it demonstrates that specific tested phenolic GRP systems can achieve demanding performance criteria in high-risk environments.

However, it must be used correctly.

US Coast Guard and ASTM F3059 evidence:

• applies to the exact tested and certified product;

• is subject to defined installation and location limits;

• supports the performance credentials of that product; but

• does not replace the requirements of UK Building Regulations, Approved Document B, the project fire strategy or the approval process for the individual building.

  
  

It is therefore a supplementary technical credential, not a universal compliance certificate for every UK service riser.

Fire safety within service risers should never be reduced to a choice between metal and composite. A protected shaft is safe because it is designed and installed as a complete fire resisting system.

That system includes:

• compartment walls and floors;

• the shaft enclosure;

• fire doors and access hatches;

• tested fire-stopping to service penetrations;

• correctly controlled openings;

• ventilation and smoke-control arrangements where required;

• inspection access;

• installation quality; and

• complete fire-safety information at handover.

  
  

The Vital GRP approach

Vital GRP does not claim that GRP is non-combustible. We do not claim that a GRP riser deck is a compartment floor or a substitute for passive fire protection.

We design and supply RiserDeck® systems as engineered fall-prevention and access solutions within coordinated service-riser arrangements.

For each project, the technical review should confirm:

1. The purpose and classification of the shaft.

2. The location and required performance of the compartment line.

3. The relationship between the deck, shaft enclosure and fire-stopping.

4. The suitability of the selected GRP system for the environment and use.

5. Any specialist fire, smoke-control, gas-ventilation or operational constraints.

6. The evidence required for the exact product and configuration.

7. The information required for project handover and future inspection.

This is a more rigorous and safer approach than treating material type as the only consideration.