8.3 Chemical Hazards, Chemistry, and Hazard Communication

Understanding Chemicals in Real Work

A chemical can harm through inhalation, skin contact, ingestion, injection, fire, explosion, oxygen displacement, corrosion, sensitization, or reaction with incompatible materials. OSHA's Hazard Communication Standard (HazCom, 29 CFR 1910.1200) — sometimes called "the right-to-know" rule and the most-cited OSHA standard year after year — is aligned with the United Nations Globally Harmonized System (GHS) of classification and labeling.

Physical Form and Chemistry Drive Exposure

Form matters more than identity alone. A solid is inert until grinding produces dust; a liquid releases vapor when heated or sprayed; welding generates metal fume; a gas can displace oxygen. Practical chemistry parameters to recognize:

• Vapor pressure / volatility — high vapor pressure means more airborne vapor at room temperature.
• Particle size — respirable particles (roughly under 10 micrometers, with the deepest-penetrating fraction near 4 µm) reach the gas-exchange region of the lung.
• pH — strong acids (low pH) and bases (high pH) cause corrosive tissue damage.
• Flash point — a flammable liquid (OSHA: flash point below 100°F) readily forms ignitable vapor.
• Reactivity / incompatibility — mixing incompatible chemicals can release heat, pressure, toxic gas, or fire.

Safety Data Sheets: A 16-Section Standard

Under GHS, every Safety Data Sheet (SDS) uses the same 16 sections in a fixed order, so reviewers know exactly where to look.

Sections 12–15 (ecological, disposal, transport, regulatory) are not OSHA-enforced, but Sections 1–11 are. An SDS supports hazard recognition but never replaces exposure assessment — the safety professional still must understand quantity, duration, ventilation, temperature, and behavior.

GHS Labels

A compliant workplace label carries six elements: product identifier, signal word ("Danger" for severe hazards, "Warning" for less severe), pictograms (such as the flame, corrosion, health-hazard, and skull-and-crossbones symbols), hazard statements (e.g., "Causes serious eye damage"), precautionary statements, and supplier identification. Workers transferring liquid into an unlabeled secondary container still need the identity and hazard communicated — a symbol alone is not training.

Storage, Nonroutine Work, and Controls

Incompatible chemicals stored together can react during a spill; acids must be segregated from bases, oxidizers from flammables and from organics. Nonroutine tasks deserve special scrutiny: a tank safe during operation can produce a toxic atmosphere during cleaning, and a filter change can release concentrated dust.

The NFPA 704 Diamond

For fixed storage, the NFPA 704 placard (the "fire diamond") rates a material 0–4 in four quadrants: blue for health, red for flammability, yellow for instability/reactivity, and white for special hazards (such as OX for oxidizer or W-bar for water-reactive). A 4 means severe; a 0 means minimal. Note that NFPA 704 rates acute emergency-response hazards for firefighters, whereas the GHS label communicates hazards to workers during normal use — the exam may contrast the two systems and their different audiences.

A Worked Compatibility Scenario

A worker is told to neutralize a spilled acid and grabs a bottle of bleach (sodium hypochlorite) thinking "chemical plus chemical equals clean." Mixing acid with hypochlorite liberates chlorine gas — a severe inhalation hazard. The exam-correct response is to consult the SDS Section 7 (handling/storage) and Section 10 (stability/reactivity) before mixing, use a designated spill kit, and never combine products without verifying compatibility. Other notorious incompatibilities include ammonia with bleach (chloramine vapor), oxidizers with organics or reducers, and water with water-reactive metals such as sodium.

Segregation of stored chemicals by compatibility class — keeping acids, bases, oxidizers, flammables, and water-reactives in separate cabinets or trays — is the engineering answer that prevents accidental mixing during a leak or earthquake.

Hierarchy of Chemical Controls

Controls should target the source and route, descending the hierarchy:

• Eliminate/substitute — replace a high-vapor-pressure solvent with a water-based product or a less volatile alternative.
• Engineering — closed transfer systems, local exhaust ventilation at the point of release, process enclosure, wet methods to suppress dust.
• Administrative — written procedures, segregated storage, limited quantities at the point of use, training.
• PPE — chemical-resistant gloves matched to the chemical's breakthrough time, splash goggles or face shield, respirators selected for the contaminant.

A frequent ASP trap is jumping straight to PPE when source control is feasible, or choosing the wrong glove polymer (nitrile resists many solvents but not all; butyl rubber suits ketones, while latex offers little chemical protection — check the SDS and a glove-selection chart for permeation rate and breakthrough time). Glove material that develops chemical breakthrough mid-task can expose skin without any visible damage, so breakthrough time must exceed the expected contact duration with a safety margin. The strongest answer combines document review, worker observation, exposure assessment, and compatibility control.

Treat chemical documents as starting points, then verify how the material behaves in the actual workplace under the actual task, quantity, temperature, and ventilation conditions in use.