Safety Moment #10: Common Process Safety Hazards - Nitrogen

Hazards of nitrogen in process facilities

The material shown here has been extracted from the ebook 52 Process Safety Moments and the book Plant Design and Operations.
 

Contents

  • Introduction
  • Oxygen Contamination
  • Breathing Air
  • Backup to Instrument Air
  • Cylinder Color Coding

Introduction

Nitrogen is an inert gas — in most situations it will not react with other chemicals. In particular, it does not support the combustion of the flammable materials that are used in the process industries. Because it is inert nitrogen has many uses on process facilities, including the blanketing of tanks, equipment purging, and as a carrier gas during catalyst regeneration.

In spite of its inert nature (and the fact that it makes up 79% of the air that we breathe), nitrogen is nevertheless a hazardous material.

The Chemical Safety Board (CSB) has published guidance to do with the hazards of nitrogen (The Hazards of Nitrogen Asphyxiation). They report that, between the years 1992 and 2002, that,

  • 85 incidents of nitrogen asphyxiation resulted in 80 deaths and 50 injuries.
  • The majority of incidents occurred in manufacturing and industrial settings, but several incidents occurred in other settings including laboratories and medical facilities.

There is a matching video.

Additional case histories are provided by OSHA at Deaths Involving the Inadvertent Connection of Air-line Respirators to Inert Gas Supplies. Some of the specific issues to do with nitrogen safety on process facilities are discussed below.

Oxygen Contamination

Given that nitrogen is often manufactured from liquid air, the possibility of oxygen contamination must be considered. If a nitrogen system is contaminated with air or oxygen, then the nitrogen may no longer be inert and it may support the combustion of flammable materials.

Breathing Air

Not only could the nitrogen be contaminated with oxygen but the supply of breathing air could have dangerously low levels of oxygen if nitrogen is mixed with it.

For these reasons, it is essential to ensure that nitrogen and air cylinders are not inadvertently switched. This can be done through the use of color coding and by providing dedicated fittings for each.

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