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Fire resistance ratings can be calculated using a method that multiplies the percent of solid material in the concrete masonry unit by the actual thickness (in inches) of the blocks to determine the hourly rating for the type of aggregate used. Contact Trenwyth for specific fire ratings.

FIRE RESISTANCE RATINGS/MINIMUM REQUIRED EQUIVALENT INCHES

Aggregate Type in
The Concrete Masonry Unit
Fire Resistance
0.5 Hr.
0.75 Hr.
1 Hr.
1.5 Hr.
2 Hr.
3 Hr.
4 Hr.
Calcareous or siliceous gravel
2.0 in.
2.4 in.
2.8 in.
3.6 in.
4.2 in.
5.3 in.
6.2 in.
Limestone, cinders or slag
1.9 in.
2.3 in.
2.7 in.
3.4 in.
4.0 in.
5.0 in.
5.9 in.
Expanded clay, shale or slate
1.8 in.
2.2 in.
2.6 in.
3.3 in.
3.6 in.
4.4 in.
5.1 in.
Expanded slag or pumice
1.5 in.
1.9 in.
2.1 in.
2.7 in.
3.2 in.
4.0 in.
4.7 in.

Calculating "Equivalent Thickness" is simply determining what the block thickness would be if the same amount of material contained in a hollow unit were re-molded without core holes.

EQUIVALENT THICKNESS OF CONCRETE MASONRY UNITS (IN INCHES)

Nominal Width
(Inches)
Equivalent Thickness
Based on Typical
Hollow Units (1)
Based on Percent Solid
(75% - semi-solid)
(100% - solid)
4
2.68 (73.8%)
2.72
3.625
6
3.09 (55.0%)
4.22
5.625
8
4.04 (53.0%)
5.72
7.625
10
4.98 (51.7%)
7.22
9.625
12
5.77 (49.6%)
8.72
11.625

CALCULATING ESTIMATED FIRE RESISTANCE EXAMPLE

An 8" hollow masonry wall is constructed of expanded slag units reported to be 53%* solid. What is the estimated fire resistance of the wall? (modular units)

Equivalent Thickness = % solid x depth
Example: .53 x 7.625 in. = 4.04 inches

From Table: 3 hr. Fire Resistance requires 4.0 inches

*Percentage solid can be calculated from net area or net volume as determined by ASTM C140 "Methods of Testing Concrete Masonry Units".

(1) Information based on data published by the National Concrete Masonry Association in NCMA TEK 7-1A, available at www.trenwyth.com.

 

 


Manufacturing Plant:
Anchor Concrete Products
Church Street
Emigsville, PA 17318
(800) 233-1924
FAX (717) 767-4023
Manufacturing Plant:
Anchor Concrete Products
975 Burnt Tavern Rd
Brick, NJ 08724
(732) 292-2674
FAX (732) 292-9685
Manufacturing Plant:
Northfield Block Company
3400 E. Bungalow Road
Morris, IL 60450
(800) 358-3003
FAX (815) 416-0382
Manufacturing Plant:
Superlite Block
4626 N. 42nd Avenue
Phoenix, AZ 85019
(800) 331-9823
FAX (623) 435-2088

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