How to Write a Safety Data Sheet (SDS): A Step-by-Step Guide

A Safety Data Sheet (SDS) is a standardised 16-section document that tells people who handle a chemical what its hazards are and how to use, store, transport and dispose of it safely. Writing one correctly is mostly a process problem: you need reliable input data, a correct hazard classification, and a disciplined way to fill each section. This guide walks through that process.

Step 1: Identify the product and the responsible supplier

Decide exactly which product the SDS covers. A product is defined by its name, its composition and its intended uses, so a change in any of them is a different product (or at least a new version). Record the supplier name, address and a 24-hour emergency telephone number. These go in Section 1.

Step 2: Gather composition data

List every ingredient with its chemical name, CAS number and concentration or concentration range. For a pure substance this is one line. For a mixture you need all hazardous components and any component that contributes to the classification. Take identities from supplier SDSs, certificates of analysis or your formulation records, not from memory. You can look up names and CAS numbers in public sources such as PubChem and the ECHA classification and labelling inventory.

Step 3: Classify the hazards

Classification is the step where mistakes are most expensive. Under the Globally Harmonized System (GHS), each hazard class (for example acute toxicity, skin corrosion or flammable liquids) has criteria, and a mixture is classified either from test data on the mixture itself or by calculating from its components using additivity formulas, cut-off values and bridging principles. Where a harmonised classification exists for a substance, use it. Where it does not, you must classify from the data you have or your supplier's classification, and say where the data came from. Our guide to GHS mixture classification explains the calculations.

Step 4: Derive the label elements

Each classification maps to label elements: a signal word (Danger or Warning), hazard statements (H-codes), precautionary statements (P-codes) and pictograms. These appear in Section 2 of the SDS and on the product label, and they must agree. See GHS label requirements.

Step 5: Complete the 16 sections

Fill the sections in order, but take values from the classification and composition rather than rewriting them. Sections 4 to 8 (first aid, firefighting, spills, handling and storage, exposure controls) are written for the hazards you identified. Sections 9 to 11 hold measured or reliable data: physical properties, stability and toxicology. Section 14 depends on how you ship. The full list is in the 16 sections of an SDS explained.

Step 6: Apply the destination rules

The 16-section format is international, but the legal details are national or regional. The United States follows OSHA's Hazard Communication Standard, the EU and UK follow CLP and REACH, and other markets add language and content requirements. Check the rules for every market you sell into. See OSHA HazCom requirements and EU CLP and REACH requirements.

Step 7: Review, version and issue

Have a competent person review the finished SDS, record the revision date and version in Section 16, and keep the previous versions. Give customers the current version with the first shipment and whenever it changes materially.

Step 8: Keep it current

An SDS is a living document. Update it when you learn new hazard information, change the formulation, or when the regulations change. See how often an SDS should be updated.

Common mistakes to avoid

• Classifying a mixture as if it were its main ingredient.
• Copying an old SDS and changing only the product name.
• Leaving Section 2 and the label inconsistent with each other.
• Filling unknown data with plausible-looking values instead of stating that data is not available.
• Forgetting to update the SDS after a formulation change.