A Quick Guide to Understanding Failure Metrics

Equipment or system failures can take a number of different forms and have varying consequences. But whether full or partial, minor or catastrophic, they all impact a business’s productivity and operations. Understanding failures and examining how we respond to them is the only way to minimize their negative impact. That is the value of failure metrics. 

In this guide, we will review the most useful and commonly used failure metrics, and set you up to use them within your organization. In no time, you’ll have the data you need to update your maintenance processes and reduce the work stoppages associated with system failures.

What are failure metrics?

Failure metrics are a set of calculations that measure the average time a team or organization spends addressing and resolving system failures or their frequency. System failures may be machine breakdowns, power outages, or any other incident that causes a system to fail to perform its function, resulting in interruptions to operations. 

Benefits of tracking failure metrics

Even organizations with the most efficient and effective maintenance teams will eventually experience equipment failures. Equipment failures cause downtime, emergency repair costs, and lost revenue. 

That is why tracking failure metrics and planning for failures is critical. Through planning, organizations can help reduce the length, cost, and overall impact of downtime. Calculating failure metrics provides a number of other benefits such as: 

• Improved asset reliability and lifespan
• Reduced maintenance costs
• Better quality control and fewer defective products
• Safer and more productive workplace
• Improved asset management and efficiency

The most common failure metrics in maintenance: MTTR vs MTBF vs MTTF

Tracking a few common failure metrics eliminates guesswork, helps maintenance managers improve their teams’ response to failures, and minimizes operational disruptions. The three most common are: 

• Mean Time to Repair (MTTR)
• Mean Time Between Failures (MTBF)
• Mean Time To Failure (MTTF)

The data points used to calculate failure metrics

Data is important but collecting and analyzing it can sometimes feel overwhelming. The good news is that calculating failure metrics is pretty simple, and only requires three key data points that most organizations can find in their maintenance histories. 

• Labor hours spent on maintenance: The amount of time it takes to complete each maintenance work order, along with the dates they were performed. 
• Number of breakdowns and repairs: The number of system failures that occurred within the time period you are measuring. 
• Operational time: The expected or planned operating hours within the time period you are measuring. 

Maintenance teams likely already document this information on paper, in spreadsheets, or more commonly, directly within software like a Computerized Maintenance Management System (CMMS). Most CMMS systems can track these numbers and calculate failure metrics for you automatically. 

What is MTTR?

Mean Time To Repair or MTTR is the average time it takes to complete a repair from start to finish. It tells a team how quickly it is responding to asset issues and failures.

By having a high-level overview of how long repairs generally take, maintenance managers can: 

• Understand how much time should be allowed for repairs
• Coordinate workloads for team members to ensure enough resources are available
• Find patterns by location, production line, asset, or team member
• Identify, investigate, and troubleshoot outliers to reduce the impact of the most costly events

Why MTTR is important

Repairs equal downtime which has a huge effect on productivity and business results. In a manufacturing environment, long mean time to repair leads to missed production deadlines, increased labor costs, loss of revenue, and various operational issues. In a facility management environment, excessive mean time to repair can seriously impact customer satisfaction, safety, and legal risk.

How to calculate MTTR

MTTR is calculated by dividing the total maintenance time in a given period of time, by the total number of repairs performed in that same period. This information can then be segmented based on other available data points important to your organization like team member or location. 

For instance, if your team is deployed 5 times in one week to repair pumps on a production line, and your records show that your team has spent a total of 3 hours (180 minutes) that week repairing pumps, the MTTR for that week is 36 minutes. 

MTTR = 180 minutes of repair time / 5 total repairs

MTTR = 36 minutes

Although each individual repair time may vary, this calculation provides a general idea of how much time is spent on each pump repair. 

Keys to improving MTTR

The primary way to improve – or lower – MTTR, is to make sure maintenance processes are as efficient as possible. That requires going back to the basics and shoring up things like:

• Spare parts and asset inventory management practices that make parts and equipment information easily accessible
• Standard operating procedures (SOPs) and maintenance checklists that streamline repairs
• Technician training that ensures team members are prepared to quickly and effectively decipher failure modes and respond to problems
• Technology and condition monitoring devices that can help provide context and shorten troubleshooting processes

What is MTBF?

Mean Time Between Failures or MTBF is the average time that passes from the end of one repair to the next failure. It tells a team how long a piece of equipment might be expected to run between unplanned breakdowns, and helps them plan for the unexpected.

By having a general idea of how long machines or systems tend to run in between failures, maintenance managers can: 

• Understand how frequently repairs might be needed
• Coordinate workloads for team members to ensure enough resources are available
• Assess and improve the effectiveness of repairs at keeping systems operational
• Determine the frequency of preventive maintenance inspections and maintenance activities that may prevent or stave off failures

Why MTBF is important

Unlike MTTR, the goal is to ensure an MTBF that is as long as possible. The longer a system or asset goes without a failure, the more it is able to produce. In addition, each asset failure runs the risk of downtime losses, workplace safety incidents, and irreparable damage to equipment. Reducing the frequency of these events dramatically reduces the risks – and costs — to the business. 

How to calculate MTBF

MTBF is calculated by dividing the total operational time in a given period of time, by the total number of failures that occurred in that same period of time. This information can then be segmented based on other data points you have available such as location, asset type, and more. 

Taking the example from above, if a specific pump on a production line fails 5 times in one week, and that pump’s total run time that week was 80 hours (or 4,800 minutes), the MTBF for that pump for that particular week is 16 hours (or 960 minutes). 

MTBF = 4,800 minutes of operational time / 5 total failures

MTBF = 960 minutes

On average, that pump has failed – and can be expected to fail – every 960 minutes. 

Keys to improving MTBF

The primary way to improve – or increase – MTBF, is to make sure maintenance processes are as effective as possible. Keeping assets in good working condition with precise preventive maintenance is key through things like:

• Effective and well-executed preventive maintenance work 
• Using high-quality replacement parts in maintenance and repairs
• Properly training machine operators to ensure optimal operating conditions and input materials
• Take extra care with aging equipment, reviewing asset logs and maintenance histories when performing maintenance work

What is MTTF?

Mean Time To Failure or MTTF is the average length of time a non-reparable item is expected to last until it needs to be replaced. It represents the lifetime of a single-use product or device, and is calculated by analyzing the performance of a large quantity of that item over a particular period of time.

By having a high-level overview of how long a non-repairable system component is expected to last, maintenance managers can: 

• Plan spare parts inventory with greater accuracy
• Evaluate parts makers and vendors based on the quality or reliability of their parts
• Predict and prevent larger system failures based on the MTTF of their non-repairable components
• Plan replacements and other preventive actions with greater accuracy

Why MTTF is important

Similar to MTBF, steps should be taken to ensure MTTF is as long as possible in order to prolong and maximize production time. Doing so ensures higher output, and minimizes risks associated with frequent failures like workplace safety incidents, and irreparable damage to equipment. 

How to calculate MTTF

MTTF is calculated by dividing the total operation time in a given period of time, by the total number of items used in that same period. Again, this information can then be segmented based on other data points you have available such as item type, purpose, or manufacturer. 

For instance, if the pump from our previous example ran for 80 hours (or 4,800 minutes), but a specific gasket on the pump had to be replaced 2 times in that same period, the MTTF for that gasket is 40 hours (or 2,400 minutes). 

MTTF = 4,800 minutes of operating time / 2 total gaskets

MTTF = 2,400 minutes

This calculation provides a general idea of the longevity that can be expected of different kinds of consumable or non-repairable items. In this case, if a more expensive gasket from a different manufacturer has an MTTF that is twice as long, a maintenance manager can now evaluate whether or not the additional cost is worth the improved MTTF.

Keys to improving MTTF

Because these are non-repairable items, the steps your maintenance team can take to extend their MTTF are minimal. The primary way to improve – or increase – MTTF, is in how these kinds of items are chosen and used.  

• Pay attention to item quality when sourcing non-repairable components
• Ensure proper preventive maintenance on the larger assets where these non-repairable items are installed
• Ensure that these non-repairable items are installed, stored, and used properly and within OEM parameters

More failure metrics

There are a number of other failure metrics that can help provide context to your maintenance practices. MTTF, MTTR, and MTBF may be three of the most common, but organizations should consider others to gain a broader picture of their maintenance operations, such as: 

• MDT (Mean Down Time): The average time a system or asset remains down once a failure has occurred. 
• MTTD (Mean Time to Detect): The average time it takes machine operators or other personnel to detect and report a failure. 
• MTTA (Mean Time to Acknowledge): The average response time by the maintenance team, once a failure occurs. 
• MTTI (Mean Time to Identify): The average time it takes your team to identify the root cause of a failure so they can begin a repair. 

Choosing (and using) the right failure metrics 

While each failure metric provides its own benefits, the real insights come from applying multiple failure metrics to your maintenance operations. By monitoring and working to improve all three (or more) failure metrics, organizations let the data point to the biggest opportunities for improvement. 

If tracking multiple failure metrics sounds complicated, numerous solutions exist to streamline the process. Create a Failure Metrics Calculator or implement a Computerized Maintenance Management System (CMMS) that will calculate, track, and analyze these metrics for you.