SO CALLED “TIGHT FITTING” SOLID CORE DOORS

INTRODUCTION

 Are our high-rise residential buildings safe?

The use of so-called “tight fitting” doors may in fact be a recipe for a disaster, even within buildings incorporating automatic sprinkler systems.

There has been a great deal of debate within Australian industry at large relating to the use of alternative solutions and the practice of fire safety engineering. One specific debate, relates to unit entry doors for sole occupancy apartments in high-rise residential apartment buildings. Many alternative solutions are resulting in the replacement of traditional fire rated doors with an alternative door specification, often that of a self closing and so called “tight fitting” solid core door. These specific alternative solutions are based on the assumption that the automatic sprinkler system and other associated fire safety sub systems, will in fact allow occupant to exit through the adjacent corridor before the onset of unsafe or untenable conditions. But will they? The author believes that there is possibly a serious misunderstanding in terms of the fire resistance and smoke leakage performance of a so called “tight fitting” solid core door, and that this door solution is not appropriate for life safety consideration, even in a sprinkler controlled fire scenario. 

This article has been prepared to give the reader some relevant information relating to the design requirements for unit entry doors for these specific applications. It introduces the concept of a “life safety door” and compares and contrasts this to traditional “fire doors”, “smoke doors” and the so called “tight fitting solid core door”. It also discusses relevant published research work specifically relating to the performance, or more specifically “lack of performance” of so called “tight fitting solid core doors” in both fully developed fire scenarios and also in simulated sprinkler controlled fire scenarios. 

Fire safety practitioners, fire safety engineers, building surveyors, fire brigade personnel and insurance underwriters need to understand the implications of moving outside the “safety net” of the deemed to satisfy requirements of the Building Code of Australia (BCA). In short, they need to specify products with proven performance, remembering that alternative solutions are meant to be “performance based” designs. They cannot rely on products such as so-called “tight fitting solid core doors” with a perceived performance, especially when there is published information suggesting inadequate performance.

The cost for a door with acceptable performance criteria may in fact be comparable to that of the so called “tight fitting solid core doors”, especially if the gaps or clearances are in fact defined in the specification and need to be carefully adhered to by the door installation company. It is not a true cost to look only at the cost of the materials. The installation cost also has a significant bearing on the overall cost. 

If your current project has “tight fitting solid core doors”, you may have to revisit the design in light of this paper.

 

Warrington Fire Research test methodology FSE021 dynamic for fire and smoke leakage measurement incorporating a standard fire resistance test

BCA DEEMED TO SATISFY PROVISIONS FOR UNIT ENTRY DOORS

For Class 2, 3 and 4 part buildings, the Building Code of Australia (BCA) includes deemed to satisfy (dts) provisions relating to unit entry doors for sole occupancy units or apartments. The requirements for Type A construction (high rise), typically require a self closing fire door with an Fire Resistance Level (FRL) of one hour (-/60/30) and compliance with AS/NZS1905/1 (fire door code).

There are some concessions in the current BCA that apply only to specific buildings that incorporate an automatic sprinkler system. These concessions apply only to Type B and C construction (low rise building with rise in storeys of 3 or 4), where a so-called self closing, “tight fitting, solid core door” is allowed in place of the one hour fire door.

The relevant clauses that relate to these concessions are given in Clause C3.11 and Specification 1.1 – Clause C3.4.

The author has not been able to ascertain what the “perceived” performance a self-closing and so-called “tight fitting, solid core” door was believed to have had when regulators first allowed this concession. In light of recent published research work and practices in other countries, the author seriously challenges the validity of this concession. It should be noted that this particular concession does date back to early Ordinance 70 days. 

FIRE DOORS (BCA COMPLIANT)

 The self closing one hour fire door, (FRL of -/60/30), as required by the dts provisions of the BCA, is required to comply with Specification C3.4 which requires compliance with AS/NZS1905/1 and fire testing to AS1530/4. These requirements result in a self closing fire door, where installation clearances restrict perimeter gaps to 3mm maximum, and door bottom / threshold gaps to 10mm maximum. 

It should be noted, that the requirement for a so-called “tight fitting” door is not considered in other national building codes and  associated  national standards. In other countries, unit entry doors to Class 2, 3 and 4 part buildings, are required to have both a fire rating and smoke leakage rating and therefore in most cases will require the use intumescent fire seals and/or smoke seals.

The combined fire and smoke door will require both a proven fire resistance rating / performance level demonstrated by a standard fire resistance test (analogous to our AS1530/4) and a maximum smoke leakage rating (at a nominated temperature of exposure and pressure differential), to a standard

Air / smoke leakage test standard (analogous to our AS/NZS1530/7). The designation for a combined fire and smoke door is by incorporating a suffix “S” with the fire resistance level / fire rating, so a unit entry door for our scenario in Australia could possibly designated as –/60/30 “S”.

There is serious technical merit to an argument that our current BCA deemed to satisfy provisions for fire doors for unit entry door applications, require an additional requirement for smoke leakage and therefore require smoke seals. This requirement will require smoke seals and not rely on the so called, “tight fitting” nature of doors, to provide smoke separation to adjoining escape corridors. (Refer to the discussion below regarding performance of tight fitting doors).  

SOLID CORE DOORS – TIGHT FITTING

(BCA COMPLAINT)

The BCA deemed to satisfy requirements for a so-called “tight fitting” and “solid core” door do not provide any associated definitions and this in itself is a problem for industry.

Solid core 

Firstly what is a “solid core” door? There is no definition in the BCA and there is no appropriate Australian Standard either. The author has heard on many occasions that the timber door standards, AS2688, AS2689 and AS1909 have definitions for “solid core doors”, but they do not. 

It is the authors view, that the term “solid core” door has evolved to differentiate against a “hollow core” door, which is a door filled with a cellular, honeycomb type cardboard core. Doors typically available here locally in Australia and referred to as “solid core” doors are doors constructed of “solid” core substrates that may include for example blockboard, particle board or solid MDF. Some laminated cores incorporating MDF with a polystyrene infill to keep their weight down are being termed as “semi solid” doors.

Without an adequate BCA definition, the use “solid core” as you can see, can or may mean different things to different people, and in terms of their relative performance in terms of fire resistance and resistance to smoke leakage in fire conditions (including sprinkler controlled scenarios), will vary considerably.

The above argument does not even touch on the frame type, the dimension of the frame’s doorstop, and the installation of the frame to the surrounding wall, which in itself opens up another “can of worms” and many more variants. 

Tight fitting

Secondly, what is the definition of “tight fitting”? Again, there is no definition in the BCA for this term also. There are a number of areas of the door, where clearances or door gaps can be and should be measured, and these include the clearance around the door, (both the perimeter clearance and the clearance at the door bottom / threshold) and the gap or clearance between the frame’s doorstop and the door leaf itself. 

One must be practical about the concept of installing and maintaining the so-called “tight fitting” door, even if the definitions are given in a subsequent amendment of the BCA. Tight fitting installation practices are hard to control in the first place, and in practice, doors may settle on their hinges after commissioning, and the perimeter and frame doorstop clearances will change with general “wear and tear” of the door in service, and with thermal conditions in the building (Heating, Ventilation and Air Conditioning), not to mention issues with changes in floor finishes.  

Even with a so called “tight fitting” door and with improved definition, and assuming clearances can be maintained, credible published research suggest that the performance of this type of door in relation to smoke spread should be of serious concern to industry.

Should a so-called ‘tight fitting’ solid core door be in the BCA in the first place and how and why did it get there? 

PERFORMANCE OF “TIGHT FITTING”
SOLID CORE DOORS

There has been some local Australian research published relating to the performance of so-called “tight fitting” solid core doors, both to fully developed fires and to simulated sprinkler controlled fires.

Fully developed fire scenarios

An industry sponsored research project, involving Loriant and Tyco was conducted by Warrington Fire Research Australia, (WFRA). Some of the findings of this industry sponsored research work have been published by the Victorian Building Control Commission (1). This research work developed and documented a test methodology, WFRA FSE 021(2), that utilised a standard AS1530/4 fire test furnace and a full-scale corridor. This test methodology has since been put forward to International Standards Organisation, (ISO), as a possible International Standard as a test methodology for combined fire and hot smoke leakage of unit entry doors leading onto adjacent escape corridors.

The results of this work clearly showed that the conditions in an escape corridor adjacent to a unit entry door incorporating a so called “tight fitting” solid core door would become untenable in only a matter of minutes for a fully developed fire scenario.

After completion and publication of this work, the author believed that the use of so-called “tight fitting” solid core doors would cease, especially for alternative solutions for high rise residential apartments where protection from the “safety blanket” of the BCA dts provisions were not available.

Most surprisingly, this was not the case. As many of these high rise residential apartment buildings incorporate automatic sprinkler systems, some designers were comfortable that sprinkler activation and the performance of so-called “tight fitting” solid core doors would result in acceptable conditions in adjacent escape corridors. But will they?

 Sprinkler controlled fire scenarios

The author published the findings of his own research work, which was based on full-scale air/smoke leakage testing of doors in the USA (3). This work measured the air/smoke leakage around so called “tight fitting” solid core doors at different exposure conditions (different temperatures and pressure differentials), which were argued to be typical of sprinkler controlled fire scenarios.

The leakage rates for a typical and so-called “tight fitting” solid core door at both ambient and medium temperature (200ºC after 30 minute exposure) and at modest pressure differentials were very significant. Some quick calculations can easily show that an adjacent corridor would in fact be filled with smoke relatively quickly, even in most sprinkler controlled fire scenarios, but especially if the sprinkler system do not operate, which is a fire scenario which should be considered for most credible fire safety engineering designs.

 FIRE SAFETY ENGINEERING RELATED TRENDS

 The author is somewhat bemused by the number of high rise residential apartments whereby so called “tight fitting” solid core doors are being specified as an acceptable design solution by way of alternative designs.

A closer look at the rationale being applied (or misapplied as the case may be) by some fire safety engineering practitioners, is that there may be an incorrect or “perceived” performance for a so called “tight fitting” solid core doors. They will NOT provide 20 or 30 minutes FRL and they will most certainly NOT provide tenable conditions in an adjacent corridor for the same period of time due to their so called “tight fitting” nature. I strongly suggest the published research work be obtained and read carefully. 

Another interesting and concerning rationale is the literal interpretation of BCA performance requirement CP2 (b). To save you rushing to your BCA, CP2(b) relates to building elements and in this case the walls, doors and other penetrations, restricting the spread of fire to a degree necessary from adjoining sole-occupancy units and to public corridors in Class 2 or 3 building or Class 4 part buildings.

Some “creative” fire safety engineering practitioners will argue that spread of fire does not include spread of smoke and therefore will consider omission of fire stopping products on penetration seals between adjacent sole-occupancy apartments and also allow the use of the so-called “tight fitting” solid core unit entry door leading onto adjacent public corridors. 

The authors view is quite simply that the literal interpretation, whereby only spread of flames from a fire, and ignoring smoke spread is a convenient and dangerous loop hole which is being exploited. The net result is clearly buildings which are NOT as safe as the current BCA dts requirements, irrespective of the ambiguous reports that are being created by some fire safety engineering organisations.

Sure, the fire safety engineering practitioners can hide behind the “degree necessary” part of the BCA requirements when challenged by peer review, but it will be interesting to see how effective this defence mechanism is if ever challenged in our infamous coronial courts. 

LIFE SAFETY DOORS

I think it is important to introduce a new term, that of a “life safety door” which will differentiate doors utilized in alternative solutions from conventional fire doors, smoke doors or combination fire & smoke doors.

The life safety door is one that has demonstrated or proven performance for fire resistance and smoke leakage, which can be applied to the relevant design fire(s) being considered by the fire safety engineer. Such a doorset, which includes the wall type, door frame, door leaf and associated hardware (inclusive of door seals), will most probably have fire test performance data to AS1530/4 (or equivalent) and separate air/ smoke data to AS/NZS1530/7 (or equivalent), or have some combined or dynamic fire and smoke leakage to a test methodology such as WFRA FSE021 (or equivalent).

These life safety doors, should also be labeled (tagged), certified and maintained in the same manner as conventional fire doors. The absence of any labeling on these doors and smoke doors for this matter causes confusion in the market place especially when essential services maintenance is subsequently conducted, by fire door maintenance companies who are looking for one hour labeled dts AS/NZS1905/1 compliant fire doors.

In some cases I have heard that these so called “life safety doors” have in fact been recommended for and even replaced with conventional fire doors during these subsequent essential service inspections.

ACOUSTIC REQUIREMENTS

There are other performance requirements that need to be considered, other than fire and smoke, and one important one is sound containment or acoustics.

The ABCB is proposing some changes to the sound containment provisions in the current BCA dts provisions which will if it is implemented, result in an airborne sound insulation requirement for unit entry doors of 25db, which loosely converts to an STC or Rw value of 28-30dB, in our old terminology. 

This will require the addition of acoustic seals or gaskets to unit entry doors and will result in the deletion of so called “tight fitting” solid core doors based on sound containment principles.

Suppliers of doors and door seals will need to ensure their systems or doorsets have the required fire, smoke and acoustic performance requirements. 

CONCLUSIONS / RECOMMENDATIONS

• The cost of a fully installed and maintained so called “tight fitting” solid core door does perhaps not result in any appreciable cost savings to the developer.

• Published research work relating to the performance of so-called “tight fitting” solid core doors, is available in the public domain, and it suggests that these doors should not be used on high rise residential apartments.

• The BCA requires definitions for both “tight fitting” and “solid core” as without these definitions there are all sorts of doors being utilized which are claimed to meet the intent of the BCA

• The existing BCA dts concession for Type B and Type C constructions, where automatic sprinkler systems are employed may not meet the performance criteria of the BCA.

• BCA performance clause CP2(b) requires clarification regarding its overall intent, specifically in relation to whether “spread of fire” in fact means “spread of fire and its effect, namely smoke”.

• All ‘life safety” doors, (those with necessary performance criteria for fire and smoke resistance capabilities), require labeling /tagging, certification and maintenance in a similar manner to those requirements outlined in AS/NZS1905/1 and AS1851/7.

• Proposed acoustic provisions will require acoustic door seals on doorsets and the design for fire and smoke cannot be conducted in isolation. 

• (1) England, J.P & Young, S.A; “Report on the Performance of Solid Core Timber Door in a Fire Test using a Standard Heating Regime”, Warrington Fire Research (Aust), Building Control Commission (Victoria), 1999 as part of FREE CD inclusive of test video footage.

• (2) Warrington Fire Research (Aust) Pty Ltd Standard FSE 021 Fire Safety Engineering Test Method for Doorsets Subject to Simulated Fully Developed Fires, Revision 1; April 2000, Warrington Fire Research (Aust).

• (3) Rakic, J; “The performance of unit entry doors when exposed to simulated sprinkler controlled fires”; Fire Australia, February 2000, pp 24 to 28. 

Australian Standards (titles)

AS/NZS1905/1 – Components for the protection of openings in fire-resistant walls, – Fire-resistant doorsets

AS1530/4 – Methods for fire tests on building materials, components and structures – Fire resistance tests of elements of building construction

AS/NZS1530/7 – Methods for fire tests on building materials, components and structures – Smoke control door and shutter assemblies – ambient and medium temperature smoke leakage test procedure

AS1851/7 – Maintenance of fire-protection equipment, Part 7 : Fire-resistant doorsets

AS2688 – Timber doors

AS2689 – Timber Doorsets

AS1909 – Installation of timber doorsets