Ch 9 pg 253-257

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Questions and Answers

What mechanism primarily holds the inverted roof in place under fire conditions?

Fasteners connecting the framework

Support beams reinforced by steel

Cross bracing in the framework

Gravity acting on the 2x4s (correct)

What is the maximum expected drop of the inverted roof when a 2x4 burns through?

5 to 6 feet

No drop at all

3 to 4 feet

1 to 2 feet (correct)

How do the main joists within the inverted roof perform under high temperatures?

They are not subjected to the highest heat for some time and remain in place (correct)

They may warp but stay in place

They are subject to the highest temperatures

They weaken significantly and collapse

In what way does the inverted roof compare to newer lightweight trusses during a fire event?

The inverted roof maintains strength despite localized damage Signup and view all the answers

What structural element supports the framework of the inverted roof?

Support leading to the main joists Signup and view all the answers

What is the recommended spacing for each row of uprights in this roof construction method?

2 feet on center Signup and view all the answers

What main characteristic distinguishes the inverted roof described in this construction?

It has a springy feel. Signup and view all the answers

During what time period was the style of roof construction discussed primarily prevalent?

1920s to 1960s Signup and view all the answers

What was the method used to create pitch in the roof during construction?

By adjusting the lengths of suspending posts. Signup and view all the answers

What is a potential misconception about the lightweight structure of the inverted roof?

It suggests an imminent failure if it feels springy. Signup and view all the answers

What is the main reason for exercising caution while cutting a standard roof?

To avoid severing parts of the 2x4 framework. Signup and view all the answers

What should firefighters rely on to assess roof conditions during a response?

An understanding of how inverted roofs behave under fire. Signup and view all the answers

Which method is preferred for recognizing an inverted roof?

During prefire inspections. Signup and view all the answers

What indication might lead firefighters to reconsider abandoning a roof?

The roof shakes slightly when struck with an axe. Signup and view all the answers

What should firefighters inspect for after cutting the first hole in an inverted roof?

Check for any existing structural supports. Signup and view all the answers

What is a significant concern when a fire involves a rain roof?

The dense black smoke can create visibility issues. Signup and view all the answers

Why is it essential for the roof team to recognize the presence of the rain roof early?

To allow quick deployment of a hose stream. Signup and view all the answers

Which method is suggested for introducing water into concealed spaces during a fire?

Utilizing a cellar nozzle or distributor. Signup and view all the answers

What advantage does containing the fire mostly to the rain roof’s second cockloft provide?

It minimizes damage to structures underneath. Signup and view all the answers

What type of fire is likely to create extremely dense smoke due to burning materials?

Fires that include tar paper in concealed spaces. Signup and view all the answers

What is a potential danger of the rain roof design?

It may lead to structural failure due to additional weight. Signup and view all the answers

What structural benefit do Insulpan panels provide compared to traditional roofing methods?

They can span large areas without additional support. Signup and view all the answers

How does the rain roof affect venting beneath the roof?

It prevents venting effectively. Signup and view all the answers

Which characteristic of Insulpan panels contributes to their effectiveness as an insulating material?

They are sandwiched between oriented strand boards. Signup and view all the answers

What effect do the multiple layers of a rain roof have on fire detection?

They create void spaces that can hide fires, complicating assessment. Signup and view all the answers

Why is the construction of a rain roof considered a cheap solution?

It leaves the existing porous roof in place while adding new layers. Signup and view all the answers

In what type of developments are Insulpan panels being primarily used?

Garden apartment and townhouse developments Signup and view all the answers

What potential fire hazard is associated with Insulpan panels?

They may produce flaming droplets during a fire. Signup and view all the answers

What was the time taken to open a hole in a rain roof during a fire operation over a supermarket?

45 minutes Signup and view all the answers

What is the typical dimension of Insulpan panels?

8 ft wide and 24 ft long Signup and view all the answers

What is the primary concern regarding Styrofoam insulation in firefighting?

It produces significant toxic smoke and intense flames. Signup and view all the answers

Why is typical ventilation technique challenged with the installed panels?

The panel thickness exceeds the cutting capacity of standard tools. Signup and view all the answers

What is a recommended method for cutting insulpan roofs under fire conditions?

Cutting from the basket of an elevating platform. Signup and view all the answers

What structural challenge do the ceilings present in taller units?

They provide no common cockloft that spreads fire in voids Signup and view all the answers

What issue arises from the chain saws used in firefighting when dealing with these panels?

Most models are limited in cutting depth due to chain guards. Signup and view all the answers

Study Notes

Roof Construction Techniques

Joists in roof construction (1920s-1960s) are supported by frameworks, with roof boards elevated above joists using 2x4s.
Flat roofs must have some pitch for effective drainage of rain and snow melt.
Traditional arrangements often employed 2x12 or 3x12 joists, with upright posts providing varying heights to create desired pitch.
Each row of supports is 1.5 inches shorter than the preceding row, ensuring gradual incline; posts are spaced 2 feet apart with 4-foot spacing between rows.
Lightweight structure of these roofs provides a distinct springy feel, but this does not indicate structural failure.

Inverted Roof Characteristics

Inverted roofs show relative stability under fire; framework relies on gravity rather than fasteners for support.
Can withstand a 2x4 burning through, with potential drop limited to a foot or two.
Main joists, located in the cockloft, remain intact and support the framework despite exposure to heat.
Unlike newer lightweight trusses, an inverted roof maintains structural integrity even when portions burn.

Inspection Protocols

Extra caution is essential when cutting standard roofs to avoid damaging 2x4 framework.
Recognizing inverted roofs during prefire inspections aids effective assessment of fire conditions.
Physical roof shaking upon striking with an axe does not necessarily mandate evacuation; conditions should be evaluated critically.

Rain Roof Hazards

Rain roofs are built over existing porous roofs, creating potential dangers during firefighting operations.
Additional weight may exceed original roof supports, risking structural failure.
Two-layer roofs hinder venting and create hidden void spaces, complicating fire assessment and rescue efforts.
Existing old tar paper under new layers can ignite, generating dense black smoke; quick deployment of hose systems is crucial in these instances.

Insulpan Panel Construction

Insulpan panels consist of Styrofoam insulation sandwiched between two OSB layers, making them highly combustible.
Typically 8 feet wide and up to 24 feet long, panels span large areas with minimal additional support, resulting in cathedral ceilings.
Firefighting challenges include toxicity of smoke and flames due to the materials, alongside difficulty accessing and venting due to panel thickness.

Trench Cut Techniques

Firefighters may struggle with the thicker construction of Insulpan panels, with some installations reaching 8.5 inches in thickness.
Standard 12-inch circular saws can only cut 4 inches deep; chain saws with a minimum 9-inch depth of cut are necessary.
Cutting should ideally be performed from an elevating platform for safety and effectiveness.
The design prevents common cockloft spread, aiding in fire control.

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Description

This section covers the structural elements of roof construction, focusing on joist and roof board arrangements typical of the early to mid-20th century. It highlights the importance of proper pitch for drainage and the complexities involved when using masonry bearing walls. Understanding these concepts is crucial for effective fire tactics and building safety.