An interactive guide to chemical safety — GHS · SDS · hazard classes · PPE · compatibility
Process SafetyOSHA 30 ✓
Because OSHA is always here. Whether you're running a dairy facility, designing a chemical process, or just reading an SDS for the first time — chemical safety is the framework that keeps you alive and out of legal trouble. Understanding it is not optional. Knowing it well is a career skill.
What is GHS?The Globally Harmonized System of Classification and Labelling of Chemicals. Adopted by OSHA in 2012 (HazCom 2012). Every chemical label and SDS in the US now follows this standard. Nine pictograms — each a red diamond with a white background — communicate the hazard category at a glance. Click any pictogram to learn what it means and when you'll see it.
The 9 GHS pictograms — click to explore
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What must be on every GHS label?
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Under HazCom 2012, every chemical label must include six elements:
1. Product identifier — name or code that matches the SDS 2. Signal word — either DANGER (more severe) or WARNING (less severe). Only one per label. 3. Hazard statements — standardized phrases describing the hazard (e.g. "Causes severe skin burns") 4. Precautionary statements — what to do to minimize exposure or harm 5. Pictograms — the red diamond symbols 6. Supplier information — name, address, phone of manufacturer/importer
DANGER = Category 1 or 2 hazards. WARNING = Category 3 and above.
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Hazard categories — what the numbers mean
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GHS assigns hazard categories (usually 1–4 or 1–5) within each hazard class. Lower number = more severe hazard.
Category 1 = most dangerous. Category 4 or 5 = least dangerous within that class.
Example — Flammable liquids:
· Category 1: flash point <23°C and initial boiling point ≤35°C (think: diethyl ether)
· Category 2: flash point <23°C and initial boiling point >35°C (think: acetone)
· Category 3: flash point ≥23°C and ≤60°C (think: ethanol)
· Category 4: flash point >60°C and ≤93°C (think: mineral spirits)
Category 1 gets DANGER. Category 3 and 4 usually get WARNING.
GHS vocabulary
GHS
Globally Harmonized System — the international standard for chemical classification and labeling.
HazCom 2012
OSHA's Hazard Communication Standard — the US implementation of GHS.
Signal word
DANGER or WARNING. One per label. DANGER = more severe.
Hazard statement
Standardized phrase describing the nature of the hazard. H-codes (H200s, H300s, etc.).
Precautionary statement
Standardized phrase for minimizing exposure. P-codes (P200s, P300s, etc.).
Pictogram
Red diamond symbol communicating hazard class at a glance.
Key facts
9 GHS pictograms total — memorize all of them.
DANGER = category 1 or 2. WARNING = less severe.
Lower category number = MORE dangerous.
Every label must have all 6 elements under HazCom 2012.
The exclamation mark (!!) is the catch-all for less severe hazards.
What is an SDS?A Safety Data Sheet — formerly called MSDS (Material Safety Data Sheet). Under HazCom 2012, every SDS must follow a standardized 16-section format. Knowing which section has what information is a practical skill. Click any section to learn what's in it and why it matters.
The 16 SDS sections — click any to expand
The critical sections
Section 2 — Hazard ID
GHS classification, signal word, pictograms, hazard and precautionary statements. Read this first.
Section 4 — First Aid
Immediate response for exposure — skin, eyes, inhalation, ingestion. Know this before you use the chemical.
Section 8 — Exposure Controls/PPE
PEL, TLV, required PPE. Tells you exactly what to wear.
Section 10 — Reactivity
What it reacts with, conditions to avoid, hazardous decomposition products.
Section 14 — Transport
UN number, proper shipping name, hazard class for DOT purposes.
SDS exam tips
16 sections — always in the same order under HazCom 2012.
Section 1: who made it. Section 2: what's dangerous about it.
PEL = OSHA legal limit. TLV = ACGIH recommendation (often more protective).
Section 9 has flash point — critical for flammable liquids.
An SDS must be accessible to workers at all times during their shift.
Physical vs. health hazardsGHS divides hazards into physical hazards (fire, explosion, reactivity) and health hazards (what it does to the human body). There are also environmental hazards. Knowing which class a chemical falls into tells you how to store it, handle it, and respond when something goes wrong.
Physical hazards
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Flammable
Gases, aerosols, liquids, or solids that can ignite. Flash point determines liquid category. The lower the flash point, the more dangerous — it ignites at lower temperatures.
Single exposure causes harm. LD₅₀ is the dose that kills 50% of test animals — lower LD₅₀ means MORE toxic. Routes: oral, dermal, inhalation.
Chlorine gas, concentrated acids and caustics, methanol
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Corrosive / Skin & Eye
Causes irreversible damage to skin or eyes on contact. Includes skin corrosion (destroys tissue) and serious eye damage (irreversible). Different from irritation.
NaOH (caustic soda in CIP), HNO₃ (acid CIP), bleach at high concentration
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Respiratory / Sensitizer
Causes respiratory sensitization (asthma-like response) or is a known/suspected carcinogen, mutagen, or reproductive toxin (CMR substances).
Chlorine gas, ammonia, formaldehyde, silica dust
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Target Organ Toxicity
Causes specific organ damage — liver, kidney, nervous system, blood. Single exposure (STOT-SE) or repeated exposure (STOT-RE). Different organs have different vulnerabilities.
Heavy metals (lead → brain), solvents (liver), carbon monoxide (blood/heart)
The dairy/food facility hazards you actually see
Caustic (NaOH) for CIP — corrosive, Category 1 skin corrosion. Acid (HNO₃ or phosphoric) for CIP — corrosive. Sodium hypochlorite (bleach/sanitizer) — oxidizer, corrosive at high concentration, releases chlorine gas if mixed with acid. Quat sanitizers — mild corrosive/irritant. CO₂ — compressed gas, asphyxiant in confined spaces. Ammonia refrigerant — toxic, corrosive, flammable. Knowing these is not academic — it's your actual job.
Key terms
Flash point
Lowest temperature at which vapors ignite when exposed to an ignition source. Lower = more flammable.
LD₅₀
Lethal dose for 50% of test population. Lower number = more acutely toxic.
Asphyxiants displace oxygen — CO₂ in confined spaces is deadly with no warning smell.
PPE is the last line of defense — not the first. Engineering controls (ventilation, closed systems, substitution) come first in the hierarchy of controls. PPE is what protects you when everything else has already been done. Matching the right PPE to the hazard is a skill, not just a checklist.
Hierarchy of controls — PPE is last
1. Elimination — remove the hazard entirely
2. Substitution — replace with a less hazardous chemical or process
No synthetic fabrics — flame-resistant clothing near ignition sources
Organic vapor cartridge respirator if above PEL
Oxidizers
Safety goggles, face shield
Chemical-resistant gloves — check for specific chemical
Chemical-resistant apron. Keep away from organics/flammables.
As required by SDS Section 8
Toxic gases (Cl₂, NH₃)
Full face respirator with appropriate cartridge
Chemical-resistant gloves
Chemical-resistant suit for high concentrations
SCBA for IDLH conditions. Supplied air for high exposure.
Biological/microbiological
Safety glasses or goggles (splash risk)
Nitrile or latex gloves
Lab coat or protective garment
N95 or above if aerosol generation. Standard precautions.
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Glove selection — not all gloves are equal
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Glove selection depends on the chemical, concentration, duration of contact, and whether you need dexterity. Key glove types:
Nitrile — good general-purpose protection. Resists oils, greases, many solvents. Common in labs and food facilities. Neoprene — better for acids, caustics, alcohols, and some organic solvents. Butyl rubber — best for ketones, esters, and many hazardous chemicals. Expensive but protective. Latex — good for biological hazards but NOT for many chemicals, and allergy risk. Avoid: standard dishwashing or household gloves for chemical work — they have no permeation data and may give false confidence.
Always check the manufacturer's chemical resistance chart for permeation breakthrough time — that's how long before the chemical gets through the glove material.
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Respirator types — N95 is not always the answer
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N95 / Particulate respirators — filter particles (dust, mist, biological aerosols). Do NOT protect against gases or vapors.
Half-face respirator with cartridges — cartridges are specific to hazard class: organic vapor (OV), acid gas, ammonia/methylamine, P100 for particulates. Must be matched to the chemical.
Full-face respirator — same cartridge system but also protects eyes. Required for higher concentrations.
SCBA (Self-Contained Breathing Apparatus) — carries its own air supply. Required for IDLH conditions or unknown atmospheres. HAZWOPER requires SCBA for Level A and B response.
Under OSHA 29 CFR 1910.134, a written respiratory protection program is required before workers wear respirators — including medical evaluation, fit testing, and training.
PPE vocabulary
Hierarchy of controls
Elimination → Substitution → Engineering → Administrative → PPE. Address hazards at the top first.
Permeation
How long before a chemical passes through a glove or suit material. Check manufacturer data.
SCBA
Self-Contained Breathing Apparatus — supplies its own air. Required at IDLH concentrations.
APF
Assigned Protection Factor — how much a respirator reduces exposure. N95: APF 10. Full-face: APF 50.
Fit test
Required before using a tight-fitting respirator. Quantitative or qualitative. Annual recertification.
PPE reminders
PPE is the last resort — engineering controls first.
Safety glasses ≠ goggles. Splash hazards need goggles.
N95 filters particles only — not gases or vapors.
Match glove material to the specific chemical — check permeation data.
Respirators require medical evaluation and fit testing under 1910.134.
Chemical incompatibility kills people. Mixing incompatible chemicals can cause fires, explosions, toxic gas release, or violent reactions. In a food facility context the most dangerous combination is one you might do accidentally — bleach and acid. Never mix cleaning and sanitizing chemicals without verifying compatibility.
The most dangerous incompatibilities
⚠️ Bleach + Acid → Chlorine Gas
Sodium hypochlorite (bleach) + any acid (vinegar, HCl, phosphoric acid) → releases chlorine gas (Cl₂). Chlorine gas is a respiratory hazard at low concentrations and can be fatal at high ones. This happens in households AND in food processing facilities during CIP if sequencing is wrong. The smell is unmistakable — evacuate immediately.
⚠️ Bleach + Ammonia → Chloramines
Sodium hypochlorite + ammonia (or ammonium compounds) → chloramine gases. Toxic, irritating, can cause respiratory damage. This is why ammonia-based cleaners and bleach-based sanitizers must never be mixed. In a dairy facility with ammonia refrigeration systems — know where your lines are.
⚠️ Oxidizers + Organics → Fire/Explosion
Oxidizing agents (hydrogen peroxide, nitric acid, bleach, permanganate) in contact with organic materials (solvents, oils, wood, paper) can ignite spontaneously or explosively. Never store oxidizers near flammable organics. Nitric acid + organic material is especially dangerous.
⚠️ Acid + Caustic → Violent Neutralization
Concentrated acids and bases neutralize exothermically — they release heat. If done rapidly or in concentrated form, the heat can cause boiling, spattering, and burns. In CIP systems, acid and caustic cycles must be fully rinsed between each other. Residual acid in a line hit by caustic can cause violent reaction.
⚠️ Peroxides + Everything
Hydrogen peroxide (especially concentrated) is a strong oxidizer that reacts violently with many materials — metals, organics, reducing agents. In dairy sanitation, PAA (peracetic acid = acetic acid + H₂O₂) is used as a sanitizer. Handle with respect — it's effective precisely because it's reactive.
⚠️ Water + Reactive Metals → Hydrogen Fire
Alkali metals (sodium, potassium, lithium) react violently with water producing hydrogen gas which ignites immediately. Less relevant in food facilities but foundational chemistry. Also: concentrated sulfuric acid + water — always add acid to water, never water to acid.
CIP chemical sequencing — your actual workflow
A standard CIP cycle: pre-rinse (water) → caustic wash (NaOH, pH 11–13) → intermediate rinse → acid wash (HNO₃ or phosphoric, pH 2–4) → final rinse → sanitizer (quat, PAA, or chlorine-based). The intermediate rinse between caustic and acid is not optional — it prevents the acid-caustic reaction and protects equipment. This is also why you verify residual chemical levels before and after each phase.
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Chemical storage compatibility — the rules
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Incompatible chemicals must be stored separately — not just on different shelves but in separate cabinets or areas with appropriate secondary containment.
Keep separate:
· Flammables away from oxidizers
· Acids away from caustics AND away from oxidizers
· Toxic chemicals in locked, ventilated storage
· Peroxides away from all organic materials
Segregation rules: Store by hazard class, not alphabetically. Chemicals whose names start with the same letter can be deadly together. "Alphabetical" storage is a documentation approach, not a safety approach.
The never mix list
Bleach + Acid
→ Chlorine gas. Evacuate immediately.
Bleach + Ammonia
→ Chloramine gases. Toxic.
Oxidizer + Organic
→ Fire or explosion risk.
Conc. Acid + Water
→ Always add acid TO water. Never reverse.
Acid + Caustic (conc.)
→ Violent exothermic neutralization.
H₂O₂ + Metal catalysts
→ Rapid decomposition, O₂ release.
CIP safety reminders
Always rinse between caustic and acid phases.
Smell of chlorine in a food facility = possible bleach-acid reaction. Evacuate.
PAA (peracetic acid) is both acidic and oxidizing — handle accordingly.
Store by hazard class — never alphabetically.
When something goes wrong — the first 60 seconds matter most. Know the plan before you need it. Emergency response in a chemical facility follows a structured process: recognize, evacuate or respond based on training, notify, contain if safe, document.
Chemical spill response — the decision tree
Step 1 — Recognize: What is it? How much? What's the hazard? Check the SDS if you don't know. If you don't know what it is, treat it as IDLH.
Step 2 — Protect yourself and others: Evacuate the area. Alert other workers. If trained and equipped — and ONLY then — consider response. If not trained for the chemical or size of spill, evacuate and call for help.
Step 3 — Notify: Call your facility's emergency number. Notify your supervisor. If the release is reportable (CERCLA/EPCRA thresholds), notify the National Response Center: 1-800-424-8802.
Step 4 — Contain (if safe and trained): Use appropriate PPE. Stop the source if possible. Contain the spill with absorbent material appropriate for the chemical. Never use combustible absorbents on oxidizers.
Step 5 — Decontaminate and document: Properly dispose of waste. Decontaminate equipment and personnel. Complete incident report. Review what happened and why.
HAZWOPER — who needs it and what it covers
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40-Hour Training
For workers at uncontrolled hazardous waste sites (e.g. Superfund cleanup). Full hazmat operations training. Covers site characterization, PPE, monitoring, decontamination.
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24-Hour Training
For workers at hazardous waste sites with less frequent or lower potential for exposure. Covers the same topics but at a reduced depth.
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8-Hour Annual Refresher
Required annually for all HAZWOPER-trained workers. Keeps knowledge current. Must cover any new regulations, procedures, or hazards encountered.
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Emergency Response (HAZWOPER 1910.120(q))
For emergency responders to unplanned releases. First Responder Awareness, Operations, Hazmat Technician, Hazmat Specialist, and On-Scene Incident Commander are the five levels.
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Process Safety Management (PSM) — 29 CFR 1910.119
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PSM applies to facilities that use highly hazardous chemicals above threshold quantities. Relevant to facilities with anhydrous ammonia refrigeration systems (threshold: 10,000 lbs).
PSM elements include: Process Hazard Analysis (PHA), Operating Procedures, Training, Mechanical Integrity, Management of Change (MOC), Emergency Planning, and Incident Investigation.
PHA is essentially HAZOP applied to a chemical process — structured team-based review asking "what could go wrong?" at each process step. The same logic as HACCP: identify hazards, evaluate likelihood and severity, put controls in place.
If your facility has an ammonia refrigeration system above 10,000 lbs, PSM applies. This is common in large dairy and food processing plants.
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HACCP and process safety — the same logic
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HACCP (food safety) and PSM/HAZOP (chemical process safety) are structurally identical frameworks:
· Both start with hazard identification
· Both evaluate likelihood and severity
· Both establish critical control points / critical safeguards
· Both require monitoring, corrective action, verification, and documentation
· Both require a trained team and periodic review
The difference is the consequence modeled: HACCP prevents pathogen contamination. PSM prevents catastrophic chemical releases. The analytical framework — think systematically about what can go wrong and put barriers in place — is exactly the same. If you can do one, you can learn the other.
Emergency vocabulary
HAZWOPER
Hazardous Waste Operations and Emergency Response — 29 CFR 1910.120. The standard for hazmat workers.
PSM
Process Safety Management — 29 CFR 1910.119. For facilities with highly hazardous chemicals above threshold.
HAZOP
Hazard and Operability Study — structured team review of a process to identify what could go wrong. Like HACCP for chemical processes.
RMP
Risk Management Plan — EPA's parallel to PSM under 40 CFR Part 68. Focuses on off-site consequences.
NRC
National Response Center — 1-800-424-8802. Required notification for reportable chemical releases.