Please note: All interim revisions for this edition available at time of your purchase will be included.

These requirements cover concrete masonry units classified for use in fire resistive walls in accordance with the conditions of acceptance of the Standard for Fire Tests of Building Construction and Materials, UL 263.

Concrete masonry units are classified as follows:

1. 2-hour units are intended for use in fire resistive walls having a rating of 2 hours or less.
2. 3-hour units are intended for use in fire resistive walls having a rating of 3 hours or less.
3. 4-hour units are intended for use in fire resistive walls having a rating of 4 hours or less.

A product that contains features, characteristics, components, materials, or systems new or different from those covered by the requirements in this standard, and that involves a risk of fire, electric shock, or injury to persons shall be evaluated using the appropriate additional component and end-product requirements to determine that the level of safety as originally anticipated by the intent of this Standard is maintained. A product whose features, characteristics, components, materials, or systems conflict with specific requirements or provisions of this standard shall not be judged to comply with this standard. Where appropriate, revision of requirements shall be proposed and adopted in conformance with the methods employed for development, revision, and implementation of this standard.