Deciphering Key Engineering Documents for Process Safety

Nov. 17, 2015
Process safety information is fundamental to any Process Safety Management initiative

In 1992 the Occupational Safety and Health Administration (OSHA) issued the Process Safety Management (PSM) program and required chemical facilities that contained over the threshold quantities of hazardous chemicals to comply with its requirements. The overall objective of the OSHA PSM program is to prevent or minimize the consequences of the catastrophic release of toxic, reactive, flammable, explosive, or highly hazardous chemicals. One of the main aspects of this program is to keep and maintain the Process Safety Information (PSI) as “living” documents.

Process Safety Information (PSI) is a very critical building block of the PSM program. PSI must be correct and kept up to date so the employees in the PSM covered facility have the accurate and vital information they need to properly handle any highly hazardous chemicals, as defined by OSHA, in their facility. PSI contains numerous engineering documents that are critical for Process Safety. PSI forms the base arch between the two pillars of the PSM program to cover and protect the personnel under that PSM program arch. 

PSI is also the connecting block to other PSM elements, such as Pre Start-up Safety Reviews (PSSRs), Mechanical Integrity (MI) programs, Standard Operating Procedures and Training.

PSI is actually broken down into three categories – the Chemical Hazards, Process Technology, and Equipment and Specifications.

The first category, chemical hazards, is essential to have documented and available so everyone working in the PSM covered area knows and understands the hazards of chemicals they are working with. The Safety Data Sheet (SDS), formerly referred to as material safety data sheets (MSDS), for the materials or chemicals being utilized contains some basic information for health, flammability, reactivity hazards, fire-fighting measures if applicable, and what to do if there is spill or exposure to the chemical. The SDS also provides some of the basic toxicity information; permissible exposure limits, physical data, reactivity data, corrosivity data, thermal and chemical stability data. The SDS should be reviewed for updates, maintained and accessible to all employees within the organization. This requirement falls under the right to know clause of the Hazard Communications Standard (HCS) which is now aligned with the Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. The Globally Harmonized System is an internationally agreed upon and accepted system which standardizes the information in the safety data sheets.

It must be noted that many types of information are normally employed in managing process safety. For example, information on the flammable properties, toxicity, and reactivity of chemical substances, and on the compatibility of chemicals with each other and with the equipment is critical to the understanding of risk and determination of adequate risk control. Information is derived from data, and data must be validly obtained and appropriate to the situation. The validity of information should not be accepted without understanding the validity of the underlying data on which it is based. Additionally, data, and therefore information, can change with time and context. Operating conditions, material properties and contaminants, equipment characteristics, and processing sequences can all impact the validity of data for a specific use.

The second category under PSI is the Process Technology. The Process Technology contains all the vital process information including the:

• Block Flow Diagrams (BFDs) and Process Flow Diagrams (PFDs); process chemistry and operations;
• Chemical inventories with the maximum intended inventory of each chemical listed and;
• Safe operating conditions of the process with upper and lower limits stated; and consequences of deviating from the specified limits.

Both OSHA and the Environmental Protection Agency (EPA) require that deviation from normal action steps be included in the operating procedures, where applicable, so they are more easily accessible to the process operators.
The third and final category, the equipment and specifications, contains the following information:

• Materials of construction;
• Process &instrumentation diagrams (P&IDs);
• Hazardous (electrical) area classification;
• Relief system design and design basis;
• Design codes and standards;
• Material and energy balances;
• Safety systems – including all interlocks, detection and/or suppression systems; and
• Any Recommended and Generally Accepted Good Engineering Practices (RAGAGEP).

PSI must be complete, up-to-date, and maintained throughout the life cycle of the process.

Engineering drawings are also key documents and part of the PSI program. The drawings are a visual tool and present a graphical language that is used to fully and clearly define all engineered items within a facility. Through an engineering drawing, an engineer can communicate his or her ideas and convey information, very precisely and without ambiguity, to the workers and operators who will build, erect, and operate the facility.

It is important that people can identify and correctly decipher the information in these engineering drawings as they are the fastest way to learn about a facility or process, learn how things work or function, build or fabricate the object or equipment, and troubleshoot potential problems within the facility.

There are four main types of engineering drawings:
1. Mechanical
2. Civil
3. Electrical
4. Chemical

Mechanical drawings include general arrangement or plot plan drawings, assembly drawings, detail and fabrication drawings for equipment and isometric drawings for piping, conduit, etc. Civil drawings can include grading and concrete foundation drawings, landscaping drawings, and architectural drawings for buildings, bridges, and other structures. Electrical drawings can include power/electrical lines, lighting and electrical schematics and communications drawings, which include DCS (Distributed Control System) and SIS (Safety Instrumented System) system drawings and electrical loop diagrams. Chemical and process drawings include BFDs, PFDs, and P&IDs. With advances in CAD (computer aided drafting) programs, a lot of drawings have now become 3-dimesional drawings and depict actual plant layouts. 

After determining what type of drawing you are looking at and its purpose, a key factor in understanding any engineering drawing is to first look for the scale and a legend for the drawing. This information is usually found on the first page. The scale will give the relative size of the drawing to “real life.” 

Understanding Engineering Drawings in Six Steps

There are generally six main steps to understanding an engineering drawing:

1. Identifying the type of drawing and its purpose;
2. Familiarizing yourself with the scale of the drawing (if applicable)
3. Identify the basic symbols on the drawing using the legend;
4. Identify the abbreviations;
5. Paying attention to the line weights, styles and colors; and
6. Look for directional arrows, detail blocks and other marks.

Besides having an understanding of the legend, it also helps to understand what the symbol actually looks like in the plant or facility. This is very important from a construction and operational standpoint to ensure the right parts and equipment are installed in the correct position during the construction phase of the project. It is also helpful for the operators to have a better understanding of what they are controlling and how changes may impact the operation of the process.

It is crucial that engineers, operators, and maintenance personnel know and understand what these valves do and in what type of situations each valve is best utilized for process control. It is also important to know what the materials of construction and various functional parts are from a process compatibility, inspection and maintenance point of view.

The information contained in this short article is only to provide a little insight on the criticality and importance of process safety information and the knowledge and understanding of how to decipher key engineering documents. It is very important to remember that PSM programs contain “living” documents that must be developed and generated and kept up to date. These documents provide the required data for hazard identification and analysis review purposes before beginning fabrication and construction. It also provides information that can help with pre-start-up safety reviews, operation procedure development and training before starting the process, operation, or facility.

Incomplete drawings can raise operation and safety questions, which may lead to stopping the PHAs and doing equipment walk-downs to confirm the process and operational procedures. Completed and up-to-date drawings helps ensure that the process can be operated and run safely without the loss of containment or release of a hazardous chemical which can impact personnel, the facility, and the environment. Drawings are also valuable in training personnel on the process or operation of equipment. Familiarity of drawings can give valuable insight in investigations should an incident occur at the facility.

These engineering drawings and documents, all part of the PSM program, must also be maintained and updated when impacted by Management of Change (MOC) and other modifications made throughout the life of the facility. When changes are not documented and the engineering drawings and documents not updated, it may lead to both minor and major incidents with resulting loss of life, injuries, and facility damage.

Walter S. Kessleris a senior process engineer and safety specialist/engineerat Chilworth Technology, Inc., a DEKRA company. He has more than 20 years of experience in process design, development andimprovement, process control,logic-controller programming, process-hazard analysis, layers-of-protectionanalysis (LOPA), safety-integrity levels (SIL) and process safety management in petroleumrefineries, gas and chemical plants, as well as pharmaceutical, manufacturing and wastewaterfacilities. Heholds a BS ChE from Pennsylvania State University and a MS BCHS fromUniversity of Houston. For more information visit or contact [email protected].

About the Author

Walter Kessler | senior specialist