Timber Fire Charring

ENGINEERING – TRUCTURAL ENGINEERING β€” MAONRY & TIMBER CALCULATOR Timber Fire Charring A precise tool.
πŸ“–
What is the Timber Fire Charring & How does it work?

When timber is exposed to fire, the outer layer undergoes pyrolysis and forms a char layer that insulates the underlying wood. The rate at which this char layer grows is called the charring rate (Ξ²) and is typically expressed in millimetres per minute for a given timber species and fire severity.

Design codes often assume a linear relationship between fire exposure time (t) and char depth (d). This simplification allows engineers to quickly estimate the residual strength of timber members after a fire event, provided that the exposure conditions are within the calibrated range of the charring rate.

In practice, a protective layer (k) such as plaster, gypsum board, or fire‑retardant coating is applied to the timber surface. This layer delays the onset of charring, and its thickness is added to the calculated char depth to obtain the effective loss of cross‑section.

d = beta times t + k
d = charring depth (mm), beta = charring rate (mm/min), t = fire exposure time (min), k = protective layer thickness (mm)
βš™οΈ
Parameters
Result β€”
❓
Frequently Asked Questions
What is the formula for calculating timber fire charring?
The char depth (d) can be calculated using the formula d = Ξ²t, where Ξ² is the charring rate in mm/min and t is the fire exposure time in minutes.
How does the charring rate vary with different timber species?
The charring rate varies depending on the timber species. Engineers typically use standardized values for common wood types to estimate char depth.
What is the significance of the char layer in timber fire resistance?
The char layer acts as an insulator, slowing down further pyrolysis and protecting the underlying wood from excessive heat, which helps maintain structural integrity.
Can you explain how to use this calculator for a specific fire exposure scenario?
Input the charring rate for your timber species and the duration of the fire exposure. The calculator will then output the expected char depth.
What are some common assumptions made in timber fire resistance calculations?
Design codes often assume a linear relationship between fire exposure time and char depth, simplifying the estimation of residual strength.
How does the charring rate change with increased fire severity?
Increased fire severity typically results in a higher charring rate, meaning the char layer forms more quickly under intense conditions.
What are some factors that can affect the accuracy of timber fire charring calculations?
Factors such as moisture content, temperature variations, and the presence of protective coatings can influence the actual charring rate and depth.

Results are for informational purposes only and do not constitute professional advice.