As part of the American Petroleum Institute Recommended Practice and the International Association of Oil & Gas Producers No. 456 industry standards, the process safety incident triangle is used to represent events from Tier 1 through Tier 4. http://corporate.exxonmobil.com/en/community/corporate-citizenship-report Safety, health and the workplace exxonmobil.com/citizenship 22 initiatives focused on improving safety in the industry.