Why do newer apparatus (post-2010) have an additional tank of diesel exhaust fluid (DEF)?

Newer fire apparatus, particularly those manufactured after 2010, are equipped with an additional tank for diesel exhaust fluid (DEF) primarily to meet stringent emission standards set by regulatory bodies. These standards aim to significantly reduce the amount of nitrogen oxides (NOx) and other harmful pollutants released into the atmosphere by diesel engines.

The introduction of DEF is part of a process known as selective catalytic reduction (SCR), where DEF is injected into the exhaust stream to facilitate a chemical reaction that converts harmful NOx gases into harmless nitrogen and water. This technology is essential for the compliance with the Environmental Protection Agency (EPA) regulations, which have become progressively stricter in response to environmental concerns.

While there may be secondary benefits of improved fuel efficiency or reduced noise levels in certain technologies, the primary reason for the incorporation of DEF in newer apparatus is to adhere to the latest emissions regulations. Ensuring that fire apparatus can operate within legal limits while minimizing their environmental impact is a key consideration for modern fire service operations.