Engineering Design and Consideration in Passive Fire

Protection – Firestopping

Andrew T.O. Laua and Selina Y. Lina

a) Hilti (Hong Kong) Ltd, 701-704 & 708A&B, 7/F, Tower A, Manulife Financial Centre, 223 Wai Yip

Street, Kwun Tong, Kowloon, Hong Kong

Abstract: Firestopping, which reinstates the fire resistance of fire compartmentation

barrier that are perforated by openings and joints, is an essential and crucial element for fire

safety design in building. With the advancement in firestopping technology and improvement

of design concept, firestopping has come to the new era of an application base. Proprietary

product design concept which is less relied on site variation and workmanship has been

adopted overwhelmingly overseas. On the other hand, firestopping design always has the

challenge to accommodate various deviations from original design/fire testing configuration to

the as-built site situation. Engineering judgement based on the firestopping principle and vast

fire testing experience are needed to assess a modification design. In this paper, we will

share the state-of-art of firestopping technology with the design concept and testing principle.

Typical firestopping applications are discussed with their special requirements and

considerations. In addition, case studies based on Hong Kong (HK) and Macau projects are

presented to showcase how to perform engineering judgement in special applications.

1. INTRODUCTION

1.1 Importance of firestopping

Failure of firestopping, even for as small size as electric cables, can lead to

catastrophic fire accidence. In January 2016, a fire engulfed the 63-storey Address

Downtown Dubai Hotel, with casualties of 1 dead and 14 injured. The aftermath investigation

reveals a spark originated from the short circuit of an outdoor spotlight on the 15th floor [1].

Fire spread indoor via spotlight electric cables due to lack of firestopping system. The

alarming system wasn’t activated since smoke detectors were only installed indoor. Fire also

spread to 14th floor by falling debris. Luckily, most of the hotel guests were able to escape

from the building in time with the alert from hotel staff. The fire accident would not have

happened if a proper firestopping system had been installed in the opening through which

the short-circuited electric cable passed. Approved firestopping systems should have

stopped the fire at its very origin and save lives and avoid tremendous property loss.

Fire safety design in buildings is of great importance to property protection and life

safety, especially in a highly populous urban city like Hong Kong which has many

skyscrapers. The fire safety designs in buildings are usually classified into four categories:

fire safety management measures, fire and smoke detection and alarm system, active

firefighting and suppression system, and passive fire protection system. The detail

descriptions of these fire safety systems are summarized in table 1. The four systems offers

fire safety measures to property and occupants throughout fire development at different

status. Each one has its own unique function and hence cannot replaced by each other.

Passive fire protection system is a ‘fail safe design’ tactic to minimize the damage to building

structural safety and threat to the lives of occupants by the division of building space into fire

compartmentation constructed with fire resisting materials. The fire compartmentation is

designed to contain fire and smoke once started at its origin and prevent their spread into

other compartments. More importantly, the fire compartmentation design maintains a safe

escape route for occupants to flee and for firefighters to rescue people trapped in the fire

scene. Each fire barrier in compartmentation should be imperforated to maintain its proper

function. In reality, fire barriers have to allow openings for access doors and building services

penetration. Access doors are required to be fire rated, in which its product certificate and

installation details are scrutinized, due to a few recent fire accident investigation exposing its

malfunction. Openings associated with building service penetrations and construction joints

shall be sealed up with firestopping materials. However, firestopping has not gained

adequate attention in current construction industry, though they are as equally important as

fire rated doors to stop fire and smoke spread. If firestopping is not designed nor constructed

properly for these joints and openings, fire and smoke will easily penetrate through them,

thus the function of fire compartmentation barrier is defeated. This results in an increase in

total fire risk, potential loss of life during a fire incident, increase in insurance premium and

overall depreciation of the property in general. In this paper, we would like to share the

firestopping engineering design principle and its advancement in technology. Firestopping

design and inspection in recent Hong Kong and Macau projects are also highlighted as case

studies.

TABLE 1. Four levels of fire safety in buildings.

Categories Example Designated Function Limitations

Fire Safety

Managemen

t Measures

• Fire safety

training

• Escape drills

1. Prevent fire accident

caused by human

2. Minimize damages

arising from fire

accident

1. It can’t eliminate possibility of

fire accident

2. Escape drills only useful before

the fire and smoke spread to

escape route

Categories Example Designated Function Limitations

Fire and

Smoke

Detection

and Alarm

System

• Automatic Fire

Alarm System

• Smoke/heat

detectors

• Break glass

1. Detect and alert when

there is fire incident

2. Activate active fire

alarm system

1. AFA system can be disabled or

malfunction

2. False alarm due to dust or

humidity caused distrust of the

system

Active Fire

Fighting

and

Suppressio

n System

• Sprinklers

• Fire hose reel

• Fire

distinguisher

1. Put away fire

automatically or

manually

2. Protect human life or

properties from fire or

smoke hazard

1. Wrong application, e.g. fire

caused by electricity should not

use water to fight

2. Rely on proper maintenance

and operation to ensure

functionality maintain

throughout the years

3. If the fire can’t be killed within a

period of time, the steam

created by sprinkler water may

speed up the spread of smoke

and temperature

Passive Fire

Protection

System

• Fire and smoke

doors

• Firestopping

1. Contain fire and smoke

from spread around the

entire building

2. Maintain the escape

route and/or refuge

floor free from fire and

smoke hazard

1. Only functional if design,

constructed and maintained

properly

2. Fire and smoke doors are often

left open due to convenience

1.2 Firestopping practice in HK and oversea

Whilst firestopping is a crucial step to reinstate a fire barrier, many misuses of

firestopping system occur due to misunderstanding of firestopping working principle. Proper

firestopping function relies on the whole firestopping system, including penetration item,

based materials and firestopping materials. It should be emphasized that firestopping is not

merely a material-based approval, instead, but shall be system consideration. A typical

misconception about firestopping is acrylic based firestop sealant applicable to seal up any

openings and joints, as long as it has the same fire resistant rating (FRR) as the fire barrier.

The fact is acrylic based firestop sealant is only applicable to narrow linear joints (usually

less than 30 mm) with limited movement requirement or narrow annular gaps around non-

combustible pipes. The firestop sealant is never able to achieve firestopping function for an

insulated pipe, although it has FRR for linear joint applications.

Currently in Hong Kong, most of the firestopping designs are delegated to installation

contractors, whereas consultants only specify the fire resistance rating of the system.

Contractors, for the sake of various reasons, tend to use one solution for all, i.e. one firestop

sealant for all firestopping systems. The vast materials submission and separated

submission of installation details hinder consultants to figure out the misuse of firestopping

materials. Furthermore, lack of firestopping mandatory inspection by third party loses the last

chance to find out the possible failure of firestopping system. Material schedules which

record all firestopping materials used has to be submitted to the Buildings Department for

occupation permit application. However, the materials schedule only lists the firestopping

materials in use, without mentioning the applications where they are used. It is impossible to

countercheck or supervise the correct firestopping application under such current system.

In Europe and North America, which have rigorous fire safety requirements for

buildings, firestop systems are designed based on approvals such as European Technology

Approvals (ETA) or Underwriter Laboratory (UL) systems. Specific design requirements are

listed clearly in these approvals, therefore system designers and applicators are easier to

follow. There are also stringent requirements to document each firestop system in a building

with identification to represent the location of the system in the building floor plans.

Systematic documentation will ensure proper installation and inspection, future maintenance

will become easier and as a result, the fire compartmentation barrier remains effective.

Independent passive fire inspector is often required in United States and it definitely

improves the final design and workmanship significantly.

2. FIRESTOPPING TECHNOLOGY

2.1 Firestopping working principle

There are two major types of firestopping applications, i.e. construction joints and

penetrations. Each of the two has its own critical consideration when designing the

firestopping systems. A simplified firestopping application design matrix is shown in table 2.

Construction joint, referring to the linear gap between two fire barriers, such as wall-to-wall,

slab-to-wall, and floor-to-floor, usually requires certain amount of movement capability due to

varied reasons, such as thermal differentials, seismicity and movement induced by wind

load. The effects of movement within the supporting construction on the fire performance of

linear joint seals, which are easily overlooked, shall be tested in accordance to the current

test standards. If materials with zero movement capacity, such as non-shrink cement grout,

is used in firestop for a linear joint with movement design, it is highly likely that fire and

smoke may leak through the movement induced gap. Firestopping materials with suitable

movement capacity should be selected to cater for the movement tolerance design. Typical

examples of joint applications with movement requirements are top of wall joint in tunnel,

curtain wall joint and precast facade joint in spandrel zone.

For penetration firestopping applications, the most critical consideration is the

combustibility of the penetration items. Combustible materials, such as plastic pipes,

insulation layers (for hot/chilled water pipe, condensation pipe and refrigerant pipe) and cable

PVC jacket, would be burnt out under fire, leading to fire and hot gases passing through the

resulted through opening. Intumescent materials, which swell and expand multiple times

under high temperature, are able to timely close up the burnt-out holes of the combustible

materials in preventing fire and smoke from passing through. Among the combustible

penetration, cables penetrations firestopping is a challenging area due to various cable sizes

and varied installation details. In short, cable penetrations happen in the following systems:

cable tray, cable trunking and cable bundle. Firestopping system selected for cable

penetration should take into account cable size, number of cables, overall opening size, and

ratios of cable cross-section area to sealing system, etc. In addition to intumescent

firestopping technology, firestop coating is another well-approved technology for cable

penetration. Firestop coating is applied on the cable surface protruding the opening, over

certain distance, for example 150 mm. The working principle of the firestop coating is to slow

down the burning of PVC jacket in order to achieve the integrity requirement in required

period.

It is worth mentioning that firestopping for penetrations also involves consideration of

the substrates and the type of fire barriers that being penetrated. Fire barriers are mainly

divided into two types, i.e. rigid and flexible. Concrete and brick wall is a typical example for

rigid fire barrier whilst dry wall made of gypsum boards is an example for flexible wall. The

base materials shall match with the configuration details in the test report.

In summary, the firestopping system selection shall base on system characteristics

and additional requirements, such as movement capacity. Critical parameters limiting the

application filed of the system, such as joint width, opening size, pipe size, etc. should be

carefully cross-checked in order to select a proper function firestopping system.

TABLE 2. Simplified firestopping applications design matrix.

Type Categories Consideration Applicable solutions

Joint

Top of wall 1. Movement requirement 1. Elastic firestop sealant with

PE rod

Curtain wall 1. Specific smoke

tightness requirement

1. Firestop spray

Precast facade joint 1. Movement requirement

2. UV and water

resistance

1. High movement silicone

based firestop sealant

Type Categories Consideration Applicable solutions

Penetration

- Pipes

Non-combustible pipe 1. Heat transfer through

the pipe

1. Elastic firestop sealant with

mineral wool

Combustible pipe 1. Pipe melt under fire 1. Intumescent firestop collar or wrap

Non-combustible pipe

with combustible

insulation

1. Insulation melt under fire 1. Intumescent firestop collar,

wrap or bandage

Penetration

- Cables

Cable Tray 1. Cable coating jacket melt under fire

2. Metal tray transfer heat

1. Firestop coated board

2. Firestop intumescent block

3. Firestop mortar with

intumescent sealant

Cable Trunking 1. There is gap inside metal trunking even if

the cables are fully filled

1. Firestop sealant for outside

the trunking

2. Firestop intumescent block

inside the trunking

Single cable or bundle 1. Cable coating jacket melt under fire

1. Firestop intumescent

sealant

2. Firestop putty disc

3. Firestop speed sleeve

Special

Application

Drywall Socket Box 1. Heat transfer if the socket box is metal

2. Fire will pass through if

the socket box is plastic

1. Firestop Putty Pad

Embedded Socket Box 1. Reduced the original rigid fire barrier

thickness

1. Firestop Putty Pad

2.2 Firestopping test standards

Firestopping performance are characterized by FRR, which typically means the

duration for which a passive fire protection system can withstand a standard fire resistance

test. This can be quantified simply as a measure of time. FRR, expressed in the format of

x/y/z in mints (for instance, 60/60/60), measures fire resistance in three criteria: stability,

integrity and insulation, respectively. Stability is applicable for load-bearing construction

elements, which is not required for firestopping. Integrity fails at the moment that a cotton

wool pad is ignited by sustained flame or hot gases through openings, or gaps developed to

certain dimension. Insulation criteria measures the time after when average temperature rise

on the non-fire exposed side shall not exceed 140 degrees Celsius and the maximum

temperature rise shall not exceed 180 degrees Celsius.

Among various international fire resistance test standards, British Standard,

European Standard and American Standard are good representatives of different levels of

standards. British standard (BS 476 Part 20 and 23) is a pure testing standard and barely

tells anything about the field of applications. Any deviation of firestopping system in a specific

project from test results needs an assessment report from accredited test laboratories. Vast

variations actually render this assessment impossible and thus projects rarely apply for

assessment report. European standards (BS EN 1366-3 and 1366-4) employs a so-called

‘standardized test configuration’. Certain application ranges are approved if the firestopping

system can pass different severe levels of test conditions. The field of applications from test

result are clearly stated in the test report. Assessment report is no longer needed for

European standard. In America, firestop systems are specifically defined by UL listings,

which go through fire test according to ASTM/UL standard and hose stream test applied after

the fire test. The reason to conduct a hose stream test is to ensure the firestop system is

capable of sustaining water pressure applied by fire hose during a fire event. Professional

engineers recognized by UL may conduct engineering judgement according to the existing

UL system and firestopping principle to create a project specific UL system. A case study of

applying engineering judgement will be discussed.

Test standards under the three international systems are summarized in Table 3. In

Hong Kong, the recognized firestopping test standards are European Standard (e.g. BS EN

1366-3, BS EN 1366-4) and British Standard (e.g. BS 476 Part 20 and Part 23) until they are

obsolete, according to the Code of Practice for Fire Safety Construction issued by Building

Department in year 2011 [2].

TABLE 3. Summary of Firestopping standard.

International

system

Approval / Listing Categories Test Standard

European (EN) ETA

Principle EN 1363-1

Joint EN 1363-4

Penetration EN 1366-3

Curtain Wall EN 1364-3 or 4

British (BS) N/A

Principle BS 476 Part 20

Joint BS 476 Part 20/23

Penetration BS 476 Part 20/23

American (UL) UL System Principle ASTM E119

International

system

Approval / Listing Categories Test Standard

Joint ASTM E1966 (UL 2079)

Penetration ASTM E814 (UL 1479)

2.4 Cutting-edge of firestopping technology

With the advancement in firestopping technology and improvement of the design

concept, firestopping has come to the new era of an application base. Proprietary product

design concept is less relied on site variation and workmanship has been adopted

overwhelmingly overseas. Preformed products, such as cast-in firestop device for

combustible penetrations with preinstalled intumescent wrap and smoke-seal strip, is a state-

of-the-art firestopping solution aimed to abolish the possibility of wrong firestopping design by

contractors. From the design and approval perspective, engineers can utilize online tools,

such as firestop product selector, to ensure the products submitted were designed for the

specific applications. Integrating the firestopping design, tender, construction and

maintenance process with the entire construction project through 3-D simulation software like

Building Information System (BIM) can highly reduce the risk for improper design due to

onsite limitation. Installation monitoring and documentation can now be done easily by cloud-

based online system with mobile apps and associated tools which is widely available in the

market.

3. FIRESTOPPING APPLICATION

As discussed in this article, there are much knowledge and consideration when

designing proper firestop application. This section intended to provide some examples and

sharing of technical considerations during the design process. However, it is important to

note that consideration and limitation is project specific, the design process may vary from

project to project. The Buildings Department has published a central data bank (CBD) to

provide historical data record on previously approved firestop products in construction

projects. However, the application and influencing parameters are not documented in the

CBD. Therefore, professional should take into consideration the application system as a

whole instead of compliance of single product when designing firestopping. In this paper,

three typical firestop applications and two case studies are discussed from the engineering

aspect to provide a brief example of designing firestop application.

3.1 Examples of typical firestop applications

3.1.1 Curtain wall perimeter joint

Curtain wall façade has become a popular design for high-rise commercial and

residential buildings in HK. To prevent fire spread externally from lower floors to upper floors,

the curtain wall should be entirely constructed with non-combustible material and vertical

spandrel zone shall be maintained. There is usually a gap of up to 150 mm in width between

the spandrel zone and curtain wall insulation back panels. The gaps, i.e., perimeter joint, if

not properly applied with firestopping at different floors, chimney effect would be easily

developed under fire, allowing smoke and fire spread upwardly quickly. The fire accidence of

First Interstate Bank in Los Angeles in May 1988 was blamed to the lack of firestopping

between the floor slabs and the skin, permitting the fire to spread from floor to floor through

this space [4]. Fire was observed spreading through this are even discovered before the

glass and mullions failed. To truly reflect the curtain wall distortion/deflection behavior under

fire, the firestopping system for the perimeter joint shall be tested in accordance to EN 1364-

3 for a full scale test or 1364-4 for a partial scale test. In addition, smoke leakage

requirement in accordance to standard EN 12101-1 shall also be carried out in order to make

sure the air tightness of the whole system. The worldwide adopted solution to achieve both

test standards consists of firestop joint spray and compressed mineral wool. This firestopping

system has the movement capacity, which is required due to wind load. Moreover, the

system is also tested to prove its effective firestopping performance for the perimeter joint

even when the curtain wall structure distorted /deflected under fire. A configuration of this

application is shown in figure 3. The influencing parameters in this application are the joint

width (w), mineral wool thickness (tB), nominal density of the mineral wool, and joint spray

thickness (tA), which shall be cross-checked to select the right system.

FIGURE 3. Configurations of curtain wall perimeter seal firestop system.

3.1.2 Lift door frame and call buttons

Lift shaft forms a vertical fire compartment and firestopping at joints and openings are

particularly important to prevent fire from spreading into the lift shaft. The gaps between the

concrete openings and the lift landing door frame, as well as the indicator panels and switch

control box (i.e. lift call buttons) shall be properly provided with firestopping. Design a firestop

solution for the lift door frame vertical gap should consider the FRR of the lift shaft, the joint

width and the depth of application. Firestop mortar with minimum 40 mm deep is one of the

possible solutions and the design is shown in figure 4. It should be noted that cement sand,

which is usually used to backfill the gaps, is not an approved firestopping materials. Spalling

of concrete [3] and cement sand under fire show its limitation to stop fire spread.

Firestopping for display panel and switch control box may also apply with firestop mortar if

the depth of firestop mortar has minimum of 40 mm. Firestop intumescent putty pad would be

the alternative solution if the thickness available at the back of control panel/indicator panel is

only a few millimeter.

FIGURE 4. Lift door frame firestopping.

3.1.3 Cable tray in a multiply-penetration opening

In most cases, cable tray penetration application comes in one opening with other

penetration services such as cable trunking and pipes as shown in Figure 5. To firestop

cable tray penetrations, a few solutions are applicable as shown in table 2 and all come with

different advantages. For example, a firestop coated board design has the advantage of easy

application and large supporting size. As for firestop block design, it benefits the end users

for frequently re-penetrate the cables. Finally firestop mortar with intumescent sealant is the

lowest material cost solution but the drawback is labor consuming and difficult for future

maintenance. If there exists a combustible pipe within the same opening, an intumescent

firestop collar instead of firestop wrap should be applied on top of a coated board system.

This is because the coated board system cannot sustain the expansion pressure of the wrap

and the firestopping function cannot achieve with this combination.

FIGURE 5. Large opening with cable tray penetration firestopping.

3.2 Case studies

3.2.1 Inspection on installations and Engineering Judgement in Macau project

The first case study sharing is a US owned casino hotel project in Macau. The

construction project is designed to International Building Code whereby all firestoppings are

designed and constructed according to UL system. Basically all typical firestop applications

are present in this project, however, due to site limitations, many typical UL system cannot

be applied directly. Since this project involved high level complexity and inexperienced local

contractor applicator in firestopping, the owner’s representative hired independent passive

fire consultant (IPFC) to oversee the design and construction processes. The first

requirement by the IPFC was to ensure all applicators equipped with relevant knowledge in

firestopping, and all applicators are mandated to attend installation training before working

onsite. Another requirement by the IPFC is the formal documentation for all firestopping

applications. Label stickers are mandatory to install in all firestopping location with reference

UL system written. This process allows inspectors to understand all the influencing

parameters listed in the UL system and compare physically onsite. In the early project phase,

some applications are designed according to standard UL systems. However, during

inspection, the IPFC found some of the influencing parameters unmatched with those

designed to UL system and instructed the contractors to seek for other solution. Engineering

judgement becomes an important tools for both irregular system and those with parameters

variances. One of the applications is the lift door frame joint, owing to the physical condition,

irregular sharp and extremely narrow, firestop mortar cannot be installed. From engineering

judgement with reference of three typical UL systems, a solution with firestop joint spray and

compressed mineral wool forming a firestopping design. The details and configuration are

shown in appendix B. Another application is a large penetration opening with cables and

pipes penetration. The opening of the onsite configuration is larger than the range in the UL

system, however since there exist penetration services supporting frame, firestop block

became a possible solution. Through engineering judgement and reference with two UL

systems, this firestopping system has formed a project specific UL system. By working with

IPFC and applying engineering judgement, the owner benefits time and capital investment

saving and achieved a smooth construction project and code compliance system.

3.2.2 Special firestopping solutions for HK A&A project

The second case study is a modernization project of a commercial office building in

Hong Kong. The scope of this project includes the relocation of plant rooms, pipe duct

rooms, waste water pipe, chilled water pipes and electric distribution system. Since the

project is carried out under occupation, the commonly used firestopping solutions that require

significant onsite installation works are not ideal. Therefore, the firestopping of this project

utilized preformed and time saving solutions, such as firestop foam, bandage, block and

coated board. The traditional firestopping design for chilled water pipe is by interrupting the

insulation material and welding a 6 mm thick metal plate in the middle of the preinstalled

metal sleeve, then applying mineral wool with firestop sealant at the gap between the pipe

and sleeve. For this project, onsite welding work is not feasible. Therefore, the firestopping

design applied firestop bandage is installed without interrupting the insulation material, as

shown in Figure 6. The installation process became much faster and easier by eliminating

the welding procedure.

FIGURE 6. Chilled water pipe protected with firestop bandage

4. CONCLUSION

Firestopping are designed to restore the fire resistance rating of fire barriers.

Incorrectly protected openings in fire barrier destroy the function of fire compartmentation for

passive fire protection, resulting in spread of fire and smoke and thus damaging the building

and threating lives. Firestopping design shall be a system consideration, instead of a product

approval regardless of its applications. Different international fire resistance test standards

are reviewed and compared. British standard is a pure testing standard while European

standards not only provide the test results but also the state the field of applications.

Moreover, fundamental firestopping principle and design consideration were briefly

introduced. In addition, three typical applications and two case studies were discussed to

serve as an example of challenges in firestopping design. To increase the fire safety of

buildings, it is important to upgrade the professional knowledge in firestopping among the

construction society and to improve installation quality through third party inspection. With

the technology advancement in firestopping, design and installation of an appropriate

firestopping system will be done effectively in the future.

APPENDIX – EXAMPLES OF ENGINEERING JUDGEMENT SOLUTIONS

REFERENCES

1. http://www.thenational.ae/uae/short-circuit-on-spotlight-blamed-for-the-address-downtown-dubai-

hotel-fire

2. Building Department, Code of Practice in Fire Safety in Buildings, 2011

3. Morita T., Nishida A., Yamazaki N., An Experimental Study on Spalling of High Strength Concrete

Elements under Fire Attack, Fire Safety Science - Proceeding of Sixth International Symposium,

France, 1999

4. https://www.usfa.fema.gov/downloads/txt/publications/tr-022.txt