Concrete Unit Masonry AHA (Activity Hazard Analysis / Job Hazard Analysis)

Updated 2026-06-23

A Concrete Unit Masonry AHA (Activity Hazard Analysis / Job Hazard Analysis) is the plan that keeps the crew building concrete unit masonry safe through the heavy block handling and ergonomics, from the masonry-wall stability and collapse, and around the block cutting silica and mortar contact. Concrete unit masonry lays concrete masonry units (block/CMU) in mortar to build walls — combining the heavy-block-handling and ergonomics hazard, the masonry-wall-stability and collapse hazard, and the block-cutting-silica and mortar-contact hazard. This guide walks through building a Concrete Unit Masonry AHA that names the heavy-block-handling/ergonomics, masonry-wall-stability/collapse, and block-cutting-silica/mortar-contact hazards and assigns the handling, stability, and silica/contact controls that hold up in the field.

Why concrete unit masonry needs its own AHA

Concrete unit masonry is the construction of walls and structures by laying concrete masonry units (CMU, concrete block) in mortar — the most common structural and partition masonry, building concrete block walls course by course, often reinforced and grouted. This closes the unit-masonry cluster and the batch. The defining feature is the concrete block itself: CMU are heavy (a standard concrete block is a heavy unit, and lifting heavy block all day is a significant ergonomic/handling hazard — more than lighter brick), the masonry-wall stability applies (concrete block walls, especially tall ones, are a major unbraced-wall-collapse concern), and cutting block generates silica (concrete block is concrete — high silica). The hazards combine the heavy-block-handling and ergonomics (the concrete blocks are heavy — the handling/ergonomic hazard (concrete masonry units are heavy, and repeatedly lifting heavy block is a significant manual-handling and ergonomic/back-injury hazard, more than lighter units)), the masonry-wall-stability and collapse (building up the block wall — the wall-stability/collapse hazard (unbraced fresh masonry walls collapse, especially under wind — and tall concrete block walls are a major concern)), the block-cutting-silica and mortar-contact (cutting concrete block (silica — concrete is high silica) and the caustic mortar (cement burns)), and the scaffold-access/falling-material. The heavy-block-handling/ ergonomics and the masonry-wall-stability/collapse justify a dedicated AHA.

Breaking concrete unit masonry into steps

The steps for a Concrete Unit Masonry AHA follow the laying:

• Set up scaffold access and material staging (block within reach)
• Mix and spread the mortar (caustic contact)
• Lay the concrete block in courses (heavy handling/ergonomics)
• Brace the wall as it is built (wall stability)
• Cut block as required (silica control)
• Manage the handling, stability, and silica hazards
• Point, clean, and cure the masonry (grout if reinforced)
• Complete

Each step carries a hazard, and the heavy-block-handling/ergonomics, the masonry-wall-stability/collapse, and the block-cutting-silica/mortar-contact are where the most significant risks concentrate.

The hazards step by step

Heavy-block-handling and ergonomics

The concrete blocks are heavy — the handling/ergonomic hazard (concrete masonry units are heavy, and repeatedly lifting heavy block is a significant manual-handling and ergonomic/back-injury hazard, more than lighter units). The controls are managing the heavy-block handling and ergonomics (concrete masonry units are heavy — a standard block is a substantial weight, and a mason lifting heavy block all day faces a significant back, shoulder, and musculoskeletal injury hazard, so staging the block within easy reach to minimize reaching/twisting with the heavy load, keeping the work at a good height, mechanical handling where possible, team lifting for the heaviest units, pacing, and rotation), and the handling/ergonomic controls. The heavy-block-handling/ergonomics is the primary defining hazard — concrete block is heavy and repeatedly lifting it is a major ergonomic hazard. (These follow the manual-handling and ergonomic fundamentals.)

Masonry-wall-stability and collapse

Building up the block wall — the wall-stability/collapse hazard (unbraced fresh masonry walls collapse, especially under wind — and tall concrete block walls are a major concern). The controls are bracing masonry walls during construction (unbraced fresh masonry walls collapse, especially under wind — and tall block walls are a major concern, so bracing per the requirements limiting unbraced masonry wall height, exclusion zones behind a wall being built), and the wall-stability controls. The masonry-wall-stability/collapse is a defining hazard — unbraced fresh block walls collapse. (These follow the masonry-wall-bracing fundamentals.)

Block-cutting-silica and mortar-contact

Cutting concrete block (silica — concrete is high silica) and the caustic mortar (cement burns). The controls are silica control for cutting concrete block (concrete block is concrete, high in silica — cutting it with a masonry saw generates respirable silica — wet cutting, dust extraction, respiratory protection), preventing skin contact with the caustic mortar (gloves, skin protection), and the silica/contact controls. The block-cutting-silica/ mortar-contact is a defining hazard. (These follow the silica and cement-contact fundamentals.)

Scaffold-access/falling-material

The scaffold access and falling material (building from scaffolds, falling heavy block/tools) carries the access/ falling-object hazard. The controls are safe scaffold access (fall protection), falling-object protection (toe boards, controlled access below — heavy block falling is especially dangerous), and the access/falling controls. (These follow the scaffold and falling-object fundamentals.)

A simple Concrete Unit Masonry AHA structure

Heavy-block handling/ergonomic control and wall-stability/silica safety

A Concrete Unit Masonry AHA centers on heavy-block handling/ergonomic control and wall-stability/silica safety. The heavy-block handling/ergonomic control addresses the heavy CMU — controlled by managing the heavy-block handling and ergonomics (staging block within reach, good work height, mechanical/team lifting for the heaviest units, pacing, rotation), since repeatedly lifting heavy block is a major injury hazard. The wall-stability/silica safety addresses the wall and the cutting — controlled by bracing masonry walls during construction (unbraced fresh block walls collapse under wind) and block-cutting silica control, plus caustic-mortar contact protection. And the scaffold access and falling material get access and falling-object controls. An AHA built on heavy-block handling/ergonomic control and wall-stability/silica safety, with access controls, addresses the hazards that define concrete unit masonry.

From the field: what actually goes wrong

In fourteen years across federal, heavy civil, and industrial projects, concrete unit masonry lays concrete masonry units in mortar, and it is the most common masonry — concrete block walls — closing the unit-masonry cluster and the batch. Its distinctive hazard within the cluster is the weight of the block. The heavy-block- handling and ergonomics hazard is a primary defining concern — concrete masonry units are heavy (a standard concrete block is a substantial weight, and heavier specialty and larger blocks more so), and a mason lays these heavy blocks continuously all day, so repeatedly lifting heavy block is a significant manual-handling and ergonomic hazard — a major cause of back, shoulder, and musculoskeletal injuries in block masons, more so than lighter brick. So managing the heavy-block handling and ergonomics (staging the block within easy reach so the mason is not reaching and twisting with the heavy load, keeping the work at a good height as the wall rises, using mechanical handling where possible, team-lifting the heaviest units, pacing, and rotating tasks) is a key control. The weight of concrete block makes handling and ergonomics the defining CMU hazard.

The masonry-wall-stability/collapse and the block-cutting-silica/mortar-contact are the other defining hazards, and the wall stability is especially acute for concrete block. On the projects I have run, concrete block walls — particularly tall ones — are a major unbraced-wall-collapse concern: a freshly laid, unbraced concrete block wall can collapse, especially under wind loads, and tall block walls (common in commercial and industrial buildings) are exactly the kind of wall that has collapsed under wind during construction, killing workers, so bracing masonry walls during construction (per the requirements limiting unbraced masonry wall height, with exclusion zones behind a wall being built or braced) is a critical control. And the block-cutting-silica hazard (concrete block is concrete, high in silica — cutting it generates respirable silica, controlled by wet cutting, dust extraction, and respiratory protection) and the caustic-mortar contact (cement burns — gloves and skin protection) are the familiar masonry material hazards. The scaffold access and the falling-material hazard (heavy block falling is especially dangerous) round it out. This closes the unit-masonry cluster and the batch. The AHA built on heavy-block handling/ergonomic control and wall-stability/silica safety is the one that protects the block-masonry crew.

The bottom line

A Concrete Unit Masonry AHA names the heavy-block-handling/ergonomics, the masonry-wall-stability/collapse, and the block-cutting-silica/mortar-contact hazards with specific controls — managing the heavy-block handling and ergonomics (repeatedly lifting heavy block is a major injury hazard), bracing masonry walls during construction (unbraced fresh block walls, especially tall ones, collapse under wind), and block-cutting silica control with caustic-mortar contact protection. The heavy-block handling/ergonomic control and the wall-stability/silica safety are the defining concerns. The AHA that manages both is the one that protects the crew.

Frequently asked questions

Why is heavy-block handling the defining CMU hazard?

Concrete masonry units are heavy (a standard concrete block is a substantial weight, heavier specialty and larger blocks more so), and a mason lays these heavy blocks continuously all day, so repeatedly lifting heavy block is a significant manual-handling and ergonomic hazard — a major cause of back, shoulder, and musculoskeletal injuries in block masons, more so than lighter brick. Controls are managing the heavy-block handling and ergonomics (staging block within reach, good work height, mechanical/team lifting for the heaviest units, pacing, rotation), and the handling/ergonomic controls.

Why is wall stability especially acute for concrete block?

Concrete block walls — particularly tall ones — are a major unbraced-wall-collapse concern: a freshly laid, unbraced concrete block wall can collapse, especially under wind, and tall block walls (common in commercial and industrial buildings) are exactly the kind that has collapsed under wind during construction, killing workers. Controls are bracing masonry walls during construction (per the requirements limiting unbraced masonry wall height, exclusion zones behind a wall being built or braced), and the wall-stability controls.

What silica and mortar hazards apply?

Concrete block is concrete, high in silica, so cutting it with a masonry saw generates respirable silica, and the caustic mortar causes cement burns from skin contact. Controls are silica control for cutting concrete block (wet cutting, dust extraction, respiratory protection), preventing skin contact with the caustic mortar (gloves, skin protection), and the silica/contact controls.

What is concrete unit masonry?

Concrete unit masonry is the construction of walls and structures by laying concrete masonry units (CMU, concrete block) in mortar — the most common structural and partition masonry, building concrete block walls course by course, often reinforced and grouted. Because concrete block is heavy (handling/ergonomic hazard), unbraced fresh block walls (especially tall ones) can collapse, and cutting block generates silica with caustic mortar, those hazards apply.

Related AHAs and JHAs

• Unit Masonry AHA — the general unit-masonry fundamentals
• Masonry Grouting AHA — the grouting of reinforced block
• Masonry Anchorage & Reinforcement AHA — the reinforcement of block masonry
• Masonry and Block Wall Construction JHA — the block-wall-construction fundamentals

Written by Mustafa Tok, CSP, ASP, CHST — OSHA Authorized Outreach Trainer with 14+ years of international construction safety experience across federal, heavy civil, and industrial projects.