---
title: "Hazardous waste: definition and classification"
subject: "Environment and Pollution Control"
chapter: 5
key: "semester_7/environment_and_pollution_control:hazardous-waste-definition-classification"
source: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/hazardous-waste-definition-classification
site: BCT Engineering
---

# Hazardous waste: definition and classification

Environment and Pollution Control · Chapter 5: Solid waste

- Asked in: year not given, 5 marks
- Video: [Hazardous Waste || 4 Types of Hazardous Waste || Four Classifications of Hazardous Waste](https://www.youtube.com/watch?v=75SU5h1PjxY) — HSE STUDY GUIDE
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/hazardous-waste-definition-classification
- Whole chapter: https://www.bctengineer.com/md/semester_7/environment_and_pollution_control/chapter-5

## Question

Define hazardous waste. Classify hazardous wastes according to their characteristics and give examples of their sources.

## Short answer

Hazardous waste poses danger to health or environment. Classified by property: ignitable (solvents, flash point <60°C), corrosive (pH ≤2 or ≥12.5), reactive (cyanides, explosives), toxic (heavy metals, pesticides), infectious (hospital sharps) and radioactive (lab waste). Sources: chemical, electroplating, tannery, hospitals, agriculture, households.

## Answer

Hazardous waste is any solid, liquid or gaseous waste that, because of its quantity or its chemical, physical or biological nature, can cause or contribute to illness or death, or can pose a danger to human health or the environment if improperly stored, treated, transported or disposed of.

#### Classification by characteristics (as used by the US EPA and in textbooks)
| Class | Property | Examples |
|---|---|---|
| **Ignitable** | Flash point < 60 $^\circ$C; burns easily | Solvents, petrol, oils, paints |
| **Corrosive** | pH $\le$ 2 or $\ge$ 12.5; attacks metals/tissue | Acids, alkalis, battery acid |
| **Reactive** | Unstable, explosive, reacts with water or releases toxic gas | Explosives, cyanides, sulphides, peroxides |
| **Toxic** | Poisonous at low dose; fails the leaching test (TCLP) | Heavy metals (Pb, Hg, Cd), pesticides, PCBs |
| **Infectious (biomedical)** | Contains pathogens | Hospital sharps, used dressings, cultures |
| **Radioactive** | Emits ionising radiation | Waste from hospitals, laboratories, research |

By form: solid, liquid, sludge, gaseous.

#### Sources
- **Industries:** chemical, pesticide, paint, tannery, electroplating, battery manufacture, metal finishing.
- **Hospitals and laboratories:** biomedical waste, chemicals, radioactive isotopes.
- **Agriculture:** pesticides, containers.
- **Households:** batteries, paints, e-waste, fluorescent lamps (small amounts).
- **Mining and energy:** tailings, fly ash, used oil.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which statement best captures why a waste is hazardous?
   A. It is produced in large volumes
   B. It can harm health or the environment if improperly stored, treated, transported or disposed of
   C. It is always liquid
   D. It has no market value
   Answer: B. Hazardous waste is defined by its potential, through quantity or chemical, physical or biological nature, to cause illness, death or environmental danger. (Key point: Definition)

2. Which property defines a corrosive hazardous waste?
   A. Flash point below 60 degC
   B. pH 2 or less, or 12.5 or more
   C. Emits ionising radiation
   D. Fails the leaching test
   Answer: B. Corrosive wastes have pH <= 2 or >= 12.5 and attack metals and tissue; flash point below 60 degC is ignitable. (Key point: Corrosive class)

3. How is a waste classed as toxic in the answer?
   A. It burns easily
   B. It contains pathogens
   C. It is poisonous at low dose and fails the leaching test (TCLP)
   D. It reacts violently with water
   Answer: C. Toxic wastes such as heavy metals, pesticides and PCBs are identified by toxicity and failing the TCLP leaching test. (Key point: Toxic class test)

## Related in Environment and Pollution Control

- [Treatment and disposal of hazardous waste](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Ahazardous-waste-management-techniques) — Environment and Pollution Control, chapter 5
- [Physical and chemical characteristics of solid waste](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Asolid-waste-characteristics) — Environment and Pollution Control, chapter 5
- [Classification and sources of air pollutants](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Aair-pollutants-classification-sources) — Environment and Pollution Control, chapter 1

## Related in other subjects

- [Point and non-point sources; waste water treatment](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Apoint-nonpoint-waste-water) — Engineering Chemistry, chapter 3
- [Classify project; characteristics; good environment](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aclassify-project-importance-environment) — Project Engineering, chapter 1
- [Turbomachines: definition and classification](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Aturbomachine-definition-classification) — Fluid Machines, chapter 1
- [Turbomachine: definition, parts and classification](https://www.bctengineer.com/question.md?key=semester_7%2Fturbo_machines%3Aturbomachine-definition-classification) — Turbo Machines, chapter 1