Data Sources and National Estimates 

Methodology Overview for the

U.S. Fire Administration’s Topical Fire 

Report Series (Volume 22)

May 2022

Mission Statement

We support and strengthen fi re and emergency medical 

services and stakeholders to prepare for, prevent, mitigate 

and respond to all hazards.

Data Sources and National Estimates 

Methodology Overview for the

U.S. Fire Administration’s Topical Fire 

Report Series (Volume 22)

National Fire Data Center

U.S. Fire Administration

May 2022

Table of contents i

Table of contents

Background ................................................................................................................... 1

Data sources.................................................................................................................. 1

National Fire Incident Reporting System ........................................................... 1

National Fire Protection Association survey estimates ................................... 2

National estimates overview...................................................................................... 3

Structures versus buildings in the National Fire Incident Reporting System 4

Residential buildings ............................................................................................. 4

Nonresidential buildings....................................................................................... 5

National estimates of building fires and losses ................................................ 6

National Fire Incident Reporting System data used in U.S. Fire Administration 

analyses................................................................................................................... 7

Data quality................................................................................................................... 9

Unknown data entries and missing values............................................................... 10

Incomplete loss reporting........................................................................................... 12

Identifying large outliers............................................................................................. 12

National Fire Incident Reporting System analytic resources................................. 12

Resources ...................................................................................................................... 13
ii Data Sources and National Estimates Methodology Overview
Background / Data sources 1

Background

The topical reports produced as part of the U.S. Fire Administration’s (USFA’s) Topical 

Fire Report Series explore facets of the fire problem in the U.S. as depicted through data 

collected in the USFA’s National Fire Incident Reporting System (NFIRS) from incidents 

reported by local response agencies. Each topical report briefly addresses the nature 

of the specific fire or fire-related topic, highlights important findings from the data, 

and may suggest other resources to consider for further information. The national 

estimates presented in the topical reports are based on data from the NFIRS and the 

National Fire Protection Association’s (NFPA’s) annual Survey of Fire Departments for 

U.S. Fire Experience.

This document addresses national estimates, as well as the data sources used to 

derive the estimates, with an emphasis on the specific NFIRS data elements analyzed 

in the topical reports. NFIRS data quality, including “unknown” data entries and 

missing data values, is also discussed. Because the majority of the USFA’s topical 

reports address fires and losses in buildings, this overview focuses on buildings.

Data sources

National Fire Incident Reporting System

The NFIRS is the world’s largest collection of data for incidents to which fire 

departments respond. These fire departments reported nearly 27 million runs or 

responses to all incidents including nearly 1.1 million fire runs in 2020.1 In 2020, the 

most recent year for available data, 20,436 fire departments reported fire incidents to 

the NFIRS.2 In 2020, 69% of U.S. fire departments reported fire incidents to the NFIRS.3

With at least two-thirds of all fire departments nationwide reporting fire incidents to 

the NFIRS, the reporting departments represent a very large data set that enables 

the USFA to develop reasonable estimates of various aspects of the fire problem. 

Although some states do require their departments to participate in the state system, 

participation in the NFIRS is voluntary. Furthermore, if a fire department is a recipient 

of a Fire Act Grant, participation is required.4 For the years 2018 to 2020, NFIRS data 

were submitted by all 50 states, the District of Columbia and Native American Tribal 

Authorities. It is important to note that not all fire departments within participating 

states report to the NFIRS.

1

NFIRS Public Data Release (PDR) file, 2020. The terminology “runs or responses” does not reflect single 

incidents but can include mutual aid responses to the same incident.

2The 20,436 fire departments reflect only those departments submitting responses that were included 

in the 2020 NFIRS PDR file. Only NFIRS valid and released incidents are included in the PDR. Mutual and 

automatic aid runs were excluded from this count to avoid counting the same incident more than once.

3For 2020, the NFPA published that there were 29,452 fire departments in the U.S. Source: NFPA, U.S. Fire 

Department Profile 2020, September 2022 (https://www.nfpa.org/-/media/Files/News-and-Research/

Fire-statistics-and-reports/Emergency-responders/osfdprofile.pdf). 4From the fiscal year (FY) 2020 Assistance to Firefighters Grant (AFG) Notice of Funding Opportunity (NOFO) — 

while NFIRS reporting is strongly encouraged, NFIRS reporting is not a requirement to apply for or be awarded 

a grant within the AFG Program. However, fire departments that receive funding under this program must 

agree to provide information to the NFIRS for the period covered by the assistance. If a recipient does not 

currently participate in the NFIRS and does not have the capacity to report at the time of the award, that 

recipient must agree to provide information to the system for a 12-month period commencing as soon as 

possible after it develops the capacity to report. Capacity to report to the NFIRS must be established prior 

to the termination of the 2-year performance period. To be compliant and close out the grant, the grantee 

may be asked by the Federal Emergency Management Agency to provide proof of compliance in reporting 

to the NFIRS. Any grantee that stops reporting to the NFIRS during the grant’s period of performance is 

subject to having the award(s) modified or withdrawn. See the FY 2020 AFG NOFO at https://www.fema.

gov/sites/default/files/documents/fema_fy-2020_afg_notice-of-funding-opportunity.pdf.
2 Data Sources and National Estimates Methodology Overview

Because the NFIRS incident reports are submitted voluntarily, the data do not 

represent a statistically selected sample. Additionally, NFIRS data are not stand-alone. 

Therefore, the USFA currently scales up raw NFIRS data or percentages to the NFPA’s 

annual national survey estimates. This approach is discussed further in the National 

Estimates Overview section.

National Fire Protection Association survey estimates

The NFPA’s Survey of Fire Departments for U.S. Fire Experience is based on a stratified 

random sample of U.S. fire departments.5 The sample of departments is stratified by 

size of community protected, and ratio estimation methodology is used to develop 

national-level summary estimates on fire-loss statistics (the total numbers of reported 

fires, fire deaths, fire injuries and direct dollar loss), as well as summary estimates of 

fires and losses by major incident types (i.e., structure, vehicle, outside and other).

The 2018 to 2020 NFPA estimates of residential structure fires and losses used to 

develop the USFA’s national estimates of residential building fires are presented in 

Table 1. From 2018 to 2020, the NFPA survey produced an annual average estimate of 

376,000 residential structure fires, resulting in 2,775 civilian fire deaths, 12,075 civilian 

fire injuries and $8.3 billion in property damage each year.6 Of these NFPA residential 

structure fire and loss estimates, 67% of fires, 55% of deaths, 51% of injuries and 55% 

of dollar losses were reported to the NFIRS during this 3-year period.

Table 1. NFPA estimates of residential structure fires and losses (2018-2020)

Year

Residential 

structure 

fires

Residential 

structure fire 

deaths

Residential 

structure fire 

injuries

Residential 

structure fire 

dollar loss

(in millions)

2018 387,000 2,820 11,600 8,286

2019 361,500 2,870 12,700 7,976

2020 379,500 2,630 11,900 8,703

Source: NFPA, “Fire Loss in the United States,” 2018 to 2020.

The 2018 to 2020 NFPA estimates of nonresidential structure fires and losses used to 

develop the USFA’s national estimates of nonresidential building fires are presented 

in Table 2. From 2018 to 2020, the NFPA survey produced an annual average estimate 

of 114,300 nonresidential structure fires, resulting in 100 civilian fire deaths, 1,125 

civilian fire injuries and $3.5 billion in property damage.7

 Of these NFPA nonresidential 

structure fire and loss estimates, 69% of fires, 76% of deaths, 58% of injuries and 79% 

of dollar losses were reported to the NFIRS during this 3-year period.

5For detailed information regarding the NFPA’s survey methodology, see the NFPA’s “Methodology 

used in calculating national estimates from NFPA’s 2021 fire experience survey,” September 2022, 

https://www.nfpa.org/-/media/Files/News-and-Research/Fire-statistics-and-reports/US-Fire-Problem/

Methodsfirelossandothers.ashx.

6Fires are rounded to the nearest 100, deaths to the nearest 5, injuries to the nearest 25 and dollar loss 

to the nearest $100 million.

7Fires are rounded to the nearest 100, deaths to the nearest 5, injuries to the nearest 25 and dollar loss 

to the nearest $100 million. 
National estimates overview 3

Table 2. NFPA estimates of nonresidential structure fires and losses 

(2018-2020)

Year Nonresidential 

structure fires

Nonresidential 

structure fire 

deaths

Nonresidential 

structure fire 

injuries

Nonresidential 

structure fire 

dollar loss

(in millions)

2018 112,000 90 1,100 2,780

2019 120,000 110 1,200 4,311

2020 111,000 100 1,100 3,404

Source: NFPA, “Fire Loss in the United States,” 2018 to 2020.

National estimates overview

National estimates presented in the USFA’s Topical Fire Report Series (Volume 22) 

are based on NFIRS data from 2018 to 2020, the NFPA’s annual surveys of structure 

fire-loss estimates from 2018 to 2020, and the USFA’s building fire-loss estimates from 

2018 to 2020.

Overall estimates of the fire problem come from the NFPA’s annual Survey of Fire 

Departments for U.S. Fire Experience.8 As previously noted, this survey produces 

national-level summary estimates on fire-loss statistics (the total numbers of reported 

fires, fire deaths, fire injuries and direct dollar loss), as well as summary estimates of 

fires and losses by major incident types (i.e., structure, vehicle, outside and other). The 

summary estimates by major incident type are further broken down to the next tier 

(e.g., residential structures, highway vehicles and the like). The raw NFPA survey data 

are not available to the public, the USFA or various other national fire data analysts.

All nationally based estimates on subsets of fire data are derived by scaling up the raw 

NFIRS data. These estimates are based on a method of apportioning the NFPA estimates 

for total fires and structure, vehicle, outside and other fires.9 Generally, these national 

estimates are derived by computing a percentage of fires, deaths, injuries or dollar loss 

in a particular NFIRS category and multiplying it by the corresponding total estimate 

from the NFPA annual survey.10 This methodology is the accepted practice of national 

fire data analysts.

One problem with this approach is that the proportions of fires and fire losses differ 

between the large NFIRS data set and the NFPA survey sample.11 Nonetheless, to be 

8For detailed information regarding the NFPA’s survey methodology, see the NFPA’s “Methodology 

used in calculating national estimates from NFPA’s 2021 fire experience survey,” September 2022,

https://www.nfpa.org/-/media/Files/News-and-Research/Fire-statistics-and-reports/US-Fire-Problem/

Methodsfirelossandothers.ashx. 9The foundation of computing national estimates is based on “The National Estimates Approach to U.S. 

Fire Statistics” by Hall, J. R. and Harwood, B., https://www.nfpa.org/-/media/Files/News-and-Research/

Fire-statistics-and-reports/NFPA-estimates-and-methodology/NationalEstimatesApproach.pdf. 10The NFPA summary estimates are used for the overall U.S. fire losses; fire losses from structure, vehicle, 

outside and other fires; and as the basis for the USFA’s estimates of residential and nonresidential building 

fires and losses. The alternative approach for these summary numbers is to use the relative percentage of 

fires (or other loss measures) from the NFIRS and scale up (multiply by) to the NFPA estimate of total fires.

11For additional information regarding the differences in proportions of fires and losses between NFIRS data 

and the NFPA survey, see the section titled “Differences between the National Fire Incident Reporting System 

data and the National Fire Protection Association survey data” in USFA’s “Fire in the United States 2008-

2017,” 20th edition, November 2019, https://www.usfa.fema.gov/downloads/pdf/publications/fius20th.pdf.
4 Data Sources and National Estimates Methodology Overview

consistent with approaches being used by other fire data analysts, the NFPA estimates 

of fires, deaths, injuries and dollar loss are used as a starting point. The details of the 

fire problem below this level are based on proportions from the NFIRS. Because the 

proportions of fires and fire losses differ between the NFIRS and the NFPA estimates, 

from time to time, this approach leads to inconsistencies. These inconsistencies will 

remain until all estimates can be derived directly from NFIRS data.

Ideally, one would like to have the data come from one consistent data source: the 

NFIRS. One of the critical pieces of data necessary to do so is missing: the overall 

population protected by all reporting fire departments. This “residential population 

protected” is not reported to the NFIRS, nor is the data easy to come by, especially 

where a county or other jurisdiction is served by several fire departments that each 

report their fires independently.

Other issues (such as full reporting because of reporting deadlines, data access and 

budgetary considerations) add a layer of complexity to using the NFIRS data to create 

estimates. Nonetheless, with such a large wealth of fire-incident data, the USFA 

believes it is possible to harness NFIRS data to produce national estimates of the U.S. 

fire problem.

Through the years, several ad hoc studies have been undertaken to identify NFIRS 

representativeness — none of which have identified major reporting issues. Most 

NFIRS data exhibit stability from one year to the next without radical changes. Results 

based on the full data set are generally similar to those based on part of the data, 

another indication of data reliability. In short, the NFIRS data are a very large and 

reasonably stable data set that is used as input to develop national estimates.

Structures versus buildings in the National Fire Incident Reporting 

System

The NFIRS allows for the differentiation between buildings and nonbuildings. In the 

NFIRS, a structure is a built object and can include nonbuildings, such as platforms, 

tents, connective structures (e.g., bridges, fences, telephone poles) and various other 

structures, in addition to buildings. Analyses of 2018 to 2020 NFIRS structure fire data 

show that, by and large, the majority (97%) of structure fires occurred in buildings.

The distinction between buildings and nonbuildings is particularly important when 

determining the effectiveness of nonbehavior-based fire safety mechanisms, such as 

smoke alarms and residential sprinklers. These important components of early fire 

detection apply to buildings and not necessarily to these other types of structures. To 

facilitate analysis of these components and to acknowledge that prevention efforts are 

generally centered on buildings, the USFA separates buildings from other structures. 

For these reasons, the USFA focuses on producing building fire and loss estimates 

separately for residential and nonresidential buildings.

Residential buildings

Table 3 shows the raw numbers of residential building fires and losses reported to the 

NFIRS from 2018 to 2020.
National estimates overview 5

Table 3. Residential building fires and losses reported to the NFIRS 

(2018-2020)

Year Residential 

building fires

Residential 

building fire 

deaths

Residential 

building fire 

injuries

Residential 

building fire 

dollar loss

(in millions)

2018 260,527 1,610 6,674 4,765

2019 256,114 1,594 6,635 4,626

2020 222,194 1,347 4,873 4,172

Source: USFA, 2018 to 2020 NFIRS.

Table 4 shows the raw numbers of residential structure fires and losses reported 

to the NFIRS from 2018 to 2020. On average, from 2018 to 2020, 98% of residential 

structure fires, 99% of associated deaths, 99% of injuries and 99% of dollar losses 

reported to the NFIRS occurred in residential buildings.

Table 4. Residential structure fires and losses reported to the NFIRS 

(2018-2020)

Year

Residential 

structure 

fires

Residential 

structure fire 

deaths

Residential 

structure fire 

injuries

Residential 

structure fire 

dollar loss

(in millions)

2018 265,572 1,627 6,714 4,818

2019 261,211 1,617 6,681 4,690

2020 226,686 1,356 4,908 4,220

Source: USFA, 2018 to 2020 NFIRS.

Nonresidential buildings

Table 5 shows the raw numbers of nonresidential building fires and losses reported 

to the NFIRS from 2018 to 2020.

Table 5. Nonresidential building fires and losses reported to the NFIRS 

(2018-2020)

Year Nonresidential 

building fires

Nonresidential 

building fire 

deaths

Nonresidential 

building fire 

injuries

Nonresidential 

building fire 

dollar loss

(in millions)

2018 73,454 69 665 2,434

2019 75,714 79 704 2,335

2020 69,044 63 465 2,166

Source: USFA, 2018 to 2020 NFIRS.
6 Data Sources and National Estimates Methodology Overview

Table 6 shows the raw numbers of nonresidential structure fires and losses reported 

to the NFIRS from 2018 to 2020. On average, 93% of nonresidential structure fires, 93% 

of deaths, 93% of injuries and 84% of dollar losses reported to the NFIRS from 2018 to 

2020 occurred in nonresidential buildings.

Table 6. Nonresidential structure fires and losses reported to the NFIRS 

(2018-2020)

Year Nonresidential 

structure fires

Nonresidential 

structure fire 

deaths

Nonresidential 

structure fire 

injuries

Nonresidential 

structure fire 

dollar loss

(in millions)

2018 79,380 74 710 2,547

2019 81,891 86 752 3,507

2020 74,110 68 500 2,241

Source: USFA, 2018 to 2020 NFIRS.

National estimates of building fires and losses

Based on the raw numbers of building fires and structure fires reported to the 

NFIRS, along with the NFPA survey estimates of structure fires, the USFA developed 

a methodology for computing national estimates of residential and nonresidential 

building fires and losses.12 The USFA uses these national building fire estimates in the 

Topical Fire Report Series, Fire Estimate Summary Series and various other fire data 

reports.13 Tables 7 and 8 present the USFA’s national estimates of fires and losses for 

residential and nonresidential buildings, respectively.

Table 7. USFA’s national estimates of residential building fires and losses 

(2018-2020)

Year Residential 

building fires

Residential 

building fire 

deaths

Residential 

building fire 

injuries

Residential 

building fire 

dollar loss — 

adjusted to 

2020 dollars

(in millions)

2018 379,600 2,790 11,525 8,446

2019 354,400 2,830 12,625 7,964

2020 372,000 2,615 11,825 8,604

Source: USFA, Fire Estimate Summary Series (2011 to 2020).

12The USFA’s methodology for computing national estimates of residential and nonresidential building 

fires and losses is detailed in the USFA’s “National Estimates Methodology for Building Fires and Losses,” 

August 2012, https://www.usfa.fema.gov/downloads/pdf/statistics/national_estimate_methodology.pdf. 13The USFA’s Fire Estimate Summary Series, as well as 2003 to 2020 national estimates of residential and 

nonresidential building fires and losses, are published at https://www.usfa.fema.gov/statistics/. The USFA’s 

Topical Fire Report Series and various other fire data reports are available at https://www.usfa.fema.gov/

statistics/reports/. 
National Fire Incident Reporting System data used in U.S. Fire Administration analyses 7

Table 8. USFA’s national estimates of nonresidential building fires and losses 

(2018-2020)

Year Nonresidential 

building fires

Nonresidential 

building fire 

deaths

Nonresidential 

building fire 

injuries

Nonresidential 

building fire 

dollar loss — 

adjusted to 

2020 dollars

(in millions)

2018 103,600 85 1,025 2,738

2019 110,900 100 1,125 2,905

2020 103,400 95 1,025 3,290

Source: USFA, Fire Estimate Summary Series (2011 to 2020).

National Fire Incident Reporting 

System data used in U.S. Fire 

Administration analyses

Although the NFIRS contains hundreds of data elements, only a few are used in 

producing the USFA’s topical reports. Most of these data elements are required to be 

completed for each fire incident type; however, for small, confined fires (i.e., Incident 

Types 113 to 118); outside rubbish fires with no value (i.e., Incident Types 150 to 155); 

and other unclassified fires, certain data elements are not required to be completed.

A complete list of NFIRS data elements is documented in the “National Fire Incident 

Reporting System Complete Reference Guide.”14 Table 9 identifies NFIRS data elements 

that are used most often in fire data analyses in the topical reports produced by the 

USFA.

Table 9. NFIRS data elements used in USFA analyses

Data element Description

Required 

data 

element

for all 

fires

Incident type The actual situation found on scene when 

emergency personnel arrived. Yes

Property use

The actual use of the property where the 

incident occurred, not the overall use of 

mixed-use properties of which the property 

is a part.

Yes

Incident date The month, day and year of the incident. Yes

14“National Fire Incident Reporting System Complete Reference Guide,” USFA, January 2015, https://www.

usfa.fema.gov/downloads/pdf/nfirs/NFIRS_Complete_Reference_Guide_2015.pdf.
8 Data Sources and National Estimates Methodology Overview

Table 9. NFIRS data elements used in USFA analyses — continued

Data element Description

Required 

data 

element

for all 

fires

Alarm time

The actual month, day, year and time of day 

(hour, minute and second) when the alarm 

was received by the fire department.

Yes

Death

A civilian fire death resulting from the 

incident or occurring during the mitigation of 

the incident (includes emergency personnel 

who are not part of the fire department, 

such as police officers or utility workers).

Yes

Injury

A civilian fire injury resulting from the 

incident or occurring during the mitigation of 

the incident (includes emergency personnel 

who are not part of the fire department, 

such as police officers or utility workers).

Yes

Dollar loss The sum of the total property and contents 

dollar losses. Yes

Fire spread15 The extent of fire spread in terms of how far 

the flame damage extended. No

Area of fire origin The primary use of the area where the fire 

started within the property. No

Heat source The source of heat that ignited the “item first 

ignited” to cause the fire. No

Item first ignited

The use or configuration of the item or 

material first ignited by the heat source. 

The item that had sufficient volume or heat 

intensity to extend to uncontrolled or selfperpetuating fire.

No

Factors contributing to 

ignition

The contributing factors that allowed the 

heat source and combustible material to 

combine to ignite the fire.

No

Presence of detectors The existence of fire-detection equipment 

within its designed range of the fire. No

Presence of automatic 

extinguishing system 

(AES)

The existence of an AES within the AES’s 

designed range of a fire. No

Source: “National Fire Incident Reporting System Complete Reference Guide,” USFA, January 2015.

15Fire spread is not a required data element for all fires. Although not required for confined fires (i.e., 

Incident Types 113 to 118), the confined fire incident types were designed to reflect small, low-loss fires, 

typically with a fire spread that is limited to the object of fire origin. In addition, fire spread is only a required 

element in the fire module when the Structure Type is coded as an enclosed building or fixed portable or 

mobile structure. Therefore, when analyzing NFIRS building fire data only, fire spread is either required 

or could be inferred for confined fires, and essentially it contains no missing data values.
Data quality 9

In addition to the data elements presented in Table 9, “fire cause” is a data characteristic 

included in almost every USFA topical report analysis; however, it is not directly 

collected in the NFIRS. Fire cause is determined for all structure fires based on an 

algorithm using cause-related data elements from the NFIRS, such as the heat source, 

item first ignited, cause of ignition, factors contributing to ignition and equipment 

involved in ignition. Fire causes are often a complex chain of events. To make it easier 

to grasp the “big picture,” 16 midlevel categories of fire causes, such as heating, cooking 

and electrical malfunction, are used by the USFA to define structure fire causes.

Structure fires are assigned to 1 of the 16 midlevel cause groupings using a hierarchy 

of definitions. A fire is included in the highest category into which it fits on the list. If it 

does not fit the top category, then the second one is considered; and if not that one, 

the third; and so on. Once a match is found, the cause is assigned, and no further 

checking of subsequent categories is done in the matrix. If no match is found, the 

incident is assigned a fire cause of “unknown.”16

Data quality

Data quality is an area of great importance. The following criteria are used in monitoring 

data in the NFIRS during the year: the data are complete, the data are accurate and the 

data are current. These criteria are monitored by creating reports from the database 

that show the number of reporting fire departments, the number of incidents by state, 

the number of invalid incidents and the number of unreleased incidents. The USFA 

provides the reports to the state NFIRS program managers and works with them to 

resolve any data issues. Technical assistance (e.g., telephone support or site visits) is 

provided to states to help address any data quality and data reporting needs.

Audits of the data are performed during the year to identify any inconsistencies. The 

audits focus on the following criteria: gaps in reporting, critical errors in the data and 

outliers in the data. In particular, the USFA works closely with states to monitor the 

quality of data coming from third-party vendor software. The USFA assists states in 

monitoring vendor data quality issues or contacts vendors directly to discuss an issue at 

a state’s request. Other data quality issues are questionable, high dollar-loss incidents 

and questionable, high numbers of fire deaths. Quarterly, USFA staff query the database 

for questionable values (i.e., outliers) and verify the values with state- and local-level 

NFIRS program managers. The data quality steps are important to ensure that the data 

meet the USFA’s criteria before the data are released in the NFIRS PDR format.

The USFA published the report “Review and Assessment of Data Quality in the 

National Fire Incident Reporting System” (May 2017). This document covers a review 

of the system, the many robust data quality checks and mechanisms which are an 

integral part of the NFIRS, and an assessment of the data quality both at the state 

level and at the data element level. The data element assessment focuses on the most 

common data elements used in NFIRS data analyses. NFIRS data were reviewed from 

the most recent years available at the time of the report’s development (2009 to 2011). 

Additionally, the report includes a section drawn from published NFPA documents 

covering the NFPA survey methodology.17

16The USFA’s detailed structure fire cause methodology and definitions are available in the document 

“National Fire Incident Reporting System Version 5.0 Fire Data Analysis Guidelines and Issues,” July 2011, 

https://www.usfa.fema.gov/downloads/pdf/nfirs/nfirs_data_analysis_guidelines_issues.pdf. 17The “Review and Assessment of Data Quality in the National Fire Incident Reporting System” document 

is available at https://www.usfa.fema.gov/downloads/pdf/publications/nfirs_data_quality_report.pdf.
10 Data Sources and National Estimates Methodology Overview

Unknown entries, incomplete loss reporting and unreported fires are also important 

considerations when assessing NFIRS data quality. These topics are discussed in more 

detail in the sections that follow.

Unknown data entries and missing 

values

On a fraction of the incident reports or casualty reports submitted to the NFIRS, the 

desired information for many data elements is either reported as “unknown” or is not 

reported at all. The total number of unknown entries or missing (i.e., blank or null) 

values is often larger than some of the important subcategories. For example, 51% of 

fatal fires in residential buildings reported from 2018 to 2020 did not have sufficient 

data recorded in the NFIRS to determine fire cause. The lack of data, especially for 

these residential fatal fires, masks the true picture of the fire problem.

Many prevention and public education programs use the NFIRS data to target at-risk 

groups or to address critical problems. Fire officials use the data in decision-making 

that affects the allocation of firefighting resources. Consumer groups and litigators 

use the data to assess product fire incidence. When the unknowns are large, the 

credibility of the data suffers. In some cases, even after the best attempts by fire 

investigators, the information is truly unknown. In other cases, the information 

reported as “unknown” in the initial NFIRS report is not updated after the fire 

investigation is completed. Reporting fire departments need to be more aware of the 

effect of incomplete data reporting and the need to update the initial NFIRS report if 

additional information is available after investigation. Efforts have been undertaken 

at the national level to encourage fire departments to close the loop on fires after 

investigations are completed.

In analyses, the unknown and missing data values should not be ignored. The 

approach taken by the USFA in presenting the data is to provide not only the “raw” 

percentages of each category, but also the “adjusted” percentages computed 

using only those incidents for which data were provided. This calculation, in effect, 

distributes the fires for which the data are unknown in the same proportion as the 

fires for which the data are known, which may or may not be approximately right. 

Both the reported data and the adjusted data (if unknowns are present) are plotted 

on bar charts in the USFA reports.

The following example illustrates distributing the fires for which the data are unknown 

using the cause of residential building fires: Cooking was determined as the fire 

cause for 41.4% of reported residential building fires from 2018 to 2020; another 

18.7% of reported fires had unknown causes. Thus, the percent of fires that had their 

cause reported was 100 minus 18.7, which equals 81.3%. With the unknown causes 

apportioned like the known causes, the adjusted percent of cooking fires in residential 

buildings can then be computed as 41.4 divided by 81.3, which equals 50.9%.

It is important to note that null and blank values are considered unreported data 

and differ in meaning and substance from “unknown” data. In data elements where 

information is required, a null or blank value may invalidate the record and cause it 

to be excluded from analyses. In addition, many fire data elements are not required 

for NFIRS confined fires (i.e., Incident Types 113 to 118) and, thus, contain missing or 

null values. Therefore, the USFA excludes confined fires from the analyses of these 

nonrequired data elements for building fires.
Unknown data entries and missing values 11

The following section focuses on data elements where information is required for 

nonconfined fires (i.e., Incident Types 111 and 120 to 123); however, the data entries 

for these elements may contain valid unknown values. Tables 10 and 11 show the 

percentages of unknown data values for NFIRS data elements that are required for 

only nonconfined residential and nonresidential building fires (i.e., the percentages 

do not reflect confined fires), respectively, with the exception of “fire cause.” Although 

the USFA’s fire cause, as previously discussed, is not a collected NFIRS data element, 

but rather assigned based on an algorithm using several cause-related data elements 

from the NFIRS, it is included in these tables for ease of presentation. It is important 

to note that percentages of unknown data values for “fire cause,” unlike the rest of 

the required data elements for nonconfined fires presented in the tables, reflect both 

confined and nonconfined fires. For 2018 to 2020, the percentages of unknown values 

for each data element in Tables 10 and 11 are relatively consistent from one year to 

the next, except for the factors contributing to ignition data element, which reflects a 

larger increase in unknown values from 2018 to 2020. In addition, for nonresidential 

building fires, the percentages of unknown values for fire cause show a large increase 

over the 3-year period.

Table 10. Percent of unknown values by specific data element for residential 

building fires reported to the NFIRS (2018-2020)

Data element

2018 2019 2020

Percent 

unknown

Percent 

unknown

Percent 

unknown

Area of fire origin 14.8 15.1 14.7

Heat source 39.9 40.3 39.6

Item first ignited 41.3 41.8 41.2

Factors contributing to ignition 32.9 34.4 35.5

Presence of detectors 31.1 30.1 29.2

Presence of AES 9.6 9.5 9.2

Fire cause 18.5 18.8 18.6

Source: NFIRS.

Table 11. Percent of unknown values by specific data element for 

nonresidential building fires reported to the NFIRS (2018-2020)

Data element

2018 2019 2020

Percent 

unknown

Percent 

unknown

Percent 

unknown

Area of fire origin 19.0 20.0 20.8

Heat source 43.6 44.3 45.4

Item first ignited 45.8 47.2 48.0

Factors contributing to ignition 34.8 36.3 39.0

Presence of detectors 20.9 20.1 20.0

Presence of AES 11.4 10.9 10.9

Fire cause 36.4 36.9 41.5

Source: NFIRS.
12 Data Sources and National Estimates Methodology Overview

Incomplete loss reporting

Although it is troublesome that insufficient data for the various NFIRS data elements 

can mask the true picture of the fire problem and impact the credibility of the data, 

the apparent nonreporting of injuries and property loss associated with many fire 

incidents is equally challenging. For example, there are many reported fires where 

the flame spread indicates damage, but property loss is not reported. It is notoriously 

difficult to estimate dollar loss, but an approximation is more useful than leaving the 

data element blank. Analysts need to be aware that this apparent lack of property-loss 

data affects the understanding of those fires that cause substantial loss.

Identifying large outliers

If the incident record clearly contains outliers, it is generally recommended to exclude 

the record from the analysis. However, before excluding such records, a quick internet 

search is completed to see if some unusual fire did occur. Additionally, if time permits, 

the USFA follows up with the fire department that submitted the incident record for 

data verification.

National Fire Incident Reporting 

System analytic resources

Several resources that provide more detailed documentation on using the NFIRS 

and NFIRS data are available. The “National Fire Incident Reporting System Complete 

Reference Guide” provides instructions for reporting data to the NFIRS and an 

understanding of the data elements collected by the system. It also serves as a 

reference for coding the data.

The document “National Fire Incident Reporting System Version 5.0 Fire Data Analysis 

Guidelines and Issues” discusses analytic considerations and methods of analyzing 

fire-incident data using NFIRS data. Topics include the NFIRS 5.0 data structure, 

general quality assurance issues, and definitions and parameters of common fire 

analyses (e.g., residential building fires or casualties), including the methodology 

for determining structure fire causes. The methods, techniques and considerations 

discussed are those used by the USFA analysts, and they do not necessarily 

reflect methods, techniques and considerations used by fire data analysts from 

other agencies and organizations. NFIRS data partners may (and do) employ their 

own methods for analyzing the data and may make differing assumptions when 

encountering data issues.

The “Review and Assessment of Data Quality in the National Fire Incident Reporting 

System” covers a review of the system, the many robust data quality checks and 

mechanisms which are an integral part of the NFIRS, and an assessment of the 

data quality both at the state level and at the data element level. The data element 

assessment focuses on the most common data elements used in NFIRS data analyses.
Resources 13

“The National Estimates Approach to U.S. Fire Statistics” is the original methodology 

for creating estimates of the U.S. fire problem using the NFPA’s annual Survey of 

Fire Departments for U.S. Fire Experience and NFIRS data. The authors present a 

detailed consensus procedure for such calculations, as well as the supporting 

rationale. “National Estimates Methodology for Building Fires and Losses” is the USFA’s 

application of the national estimates approach to building fires and fire losses. It 

details the USFA’s current fire data estimation methodology for all building fires (i.e., 

residential and nonresidential) and associated losses.

The USFA’s “Fire in the United States 2008-2017” is a statistical portrait of the 

national fire problem and provides an in-depth discussion of the data sources and 

the methodologies used to incorporate these data into fire analyses. Lastly, the “Fire 

Data Analysis Handbook” is a resource for those unfamiliar with basic data analysis 

techniques and their applicability to fire-data based analyses.

Resources

Hall, J., & Harwood, B. (1989, May). The national estimates approach to U.S. fire 

statistics. Fire Technology, 25(2), 99–113. https://www.nfpa.org/-/media/Files/Newsand-Research/Fire-statistics-and-reports/NFPA-estimates-and-methodology/

NationalEstimatesApproach.pdf

U.S. Fire Administration. (2011). National Fire Incident Reporting System version 5.0 fire 

data analysis guidelines and issues. https://www.usfa.fema.gov/downloads/pdf/

nfirs/nfirs_data_analysis_guidelines_issues.pdf

U.S. Fire Administration. (2012). National estimates methodology for building fires and 

losses. https://www.usfa.fema.gov/downloads/pdf/statistics/national_estimate_

methodology.pdf

U.S. Fire Administration. (2015). National Fire Incident Reporting System complete 

reference guide. https://www.usfa.fema.gov/downloads/pdf/nfirs/NFIRS_Complete_

Reference_Guide_2015.pdf

U.S. Fire Administration. (2017). Review and assessment of data quality in the National 

Fire Incident Reporting System. https://www.usfa.fema.gov/downloads/pdf/

publications/nfirs_data_quality_report.pdf

U.S. Fire Administration. (2019). Fire in the United States 2008-2017 (20th ed.). https://

www.usfa.fema.gov/downloads/pdf/publications/fius20th.pdf

U.S. Fire Administration. (2021). Fire data analysis handbook (3rd ed.). https://www.

usfa.fema.gov/downloads/pdf/publications/fa-266.pdf