Data Sources and National Estimates 

Methodology Overview for the 

U.S. Fire Administration’s Topical Fire 

Report Series (Volume 21)

May 2021

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 21)

National Fire Data Center

U.S. Fire Administration

May 2021

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...................................................................... 9

Incomplete loss reporting.................................................................................................. 11

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). 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 over 28.5 million runs or responses to all 

incidents including nearly 1.1 million fire runs in 2019.1 In 2019, the most recent year for 

available data, 21,331 fire departments reported fire incidents to the NFIRS.2 In 2019, 72% 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 dataset 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 

2017 to 2019, NFIRS data were submitted by all 50 states, the District of Columbia, Native 

American Tribal Authorities and the American Samoa territory. It is important to note that 

not all fire departments within participating states report to the NFIRS.

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.

1

National Fire Incident Reporting System (NFIRS) Public Data Release (PDR) file, 2019. The terminology “runs 

or responses” does not reflect single incidents but can include mutual aid responses to the same incident.

2The 21,331 fire departments reflect only those departments submitting responses that were included in the 

2019 NFIRS PDR file. Only NFIRS valid and released incidents are included in the PDR. Mutual and automatic 

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

3For 2018, the National Fire Protection Association (NFPA) estimated that there were 29,705 fire departments in the 

U.S. Source: NFPA, U.S. Fire Department Profile 2018, NFPA report - U.S. fire department profile, February 2020. 4From the fiscal year (FY) 2019 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 1-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 2019 

AFG NOFO at FY 19 Assistance to Firefighters (AFG) Notice of Funding Opportunity (NOFO) (fema.gov).
2 Data Sources and National Estimates Methodology Overview

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 nationallevel 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 2017 to 2019 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 

2017 to 2019, the NFPA survey produced an annual average estimate of 375,800 residential 

structure fires, resulting in 2,800 civilian fire deaths, 11,725 civilian fire injuries and $8.1 

billion in property damage each year.6 Of these NFPA residential structure fire and loss 

estimates, 70% of fires, 58% of deaths, 56% of injuries and 60% of dollar losses were 

reported to the NFIRS during this 3-year period.

Table 1. NFPA estimates of residential structure fires and losses (2017-2019)

Year Residential 

structure fires

Residential 

structure fire 

deaths

Residential 

structure fire 

injuries

Residential 

structure fire 

dollar loss

(in millions)

2017 379,000 2,710 10,910 7,900

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

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

Source: NFPA, “Fire Loss in the United States,” 2017 to 2019.

The 2017 to 2019 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 2017 to 2019, the NFPA survey produced an annual average estimate of 

117,300 nonresidential structure fires, resulting in 100 civilian fire deaths, 1,175 civilian fire 

injuries and $3.3 billion in property damage.7 Of these NFPA nonresidential structure fire 

and loss estimates, 68% of fires, 75% of deaths, 61% of injuries and 93% of dollar losses 

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

Table 2. NFPA estimates of nonresidential structure fires and losses (2017-2019)

Year Nonresidential 

structure fires

Nonresidential 

structure fire 

deaths

Nonresidential 

structure fire 

injuries

Nonresidential 

structure fire 

dollar loss

(in millions)

2017 120,000 105 1,250 2,800

2018 112,000 90 1,100 2,780

2019 120,000 110 1,200 4,311

Source: NFPA, “Fire Loss in the United States,” 2017 to 2019.

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

calculating national estimates from NFPA’s fire experience survey,” September 2020, 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

National estimates overview

National estimates presented in the USFA’s Topical Fire Report Series (Volume 21) are 

based on NFIRS data from 2017 to 2019, the NFPA’s annual surveys of structure fire-loss 

estimates from 2017 to 2019, and the USFA’s building fire-loss estimates from 2017 to 2019.

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 nationallevel 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 dataset and the NFPA survey sample.11 Nonetheless, to be 

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 1 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.

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

calculating national estimates from NFPA’s fire experience survey,” September 2020, 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-statisticsand-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

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 dataset 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 dataset 

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 2017 to 2019 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 2017 to 2019.

Table 3. Residential building fires and losses reported to the NFIRS (2017-2019)

Year Residential 

building fires

Residential 

building fire 

deaths

Residential 

building fire 

injuries

Residential 

building fire 

dollar loss

(in millions)

2017 257,536 1,593 6,390 4,806

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

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

Source: USFA, 2017 to 2019 NFIRS.

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

NFIRS from 2017 to 2019. On average, from 2017 to 2019, 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.
National estimates overview 5

Table 4. Residential structure fires and losses reported to the NFIRS (2017-2019)

Year Residential 

structure fires

Residential 

structure fire 

deaths

Residential 

structure fire 

injuries

Residential 

structure fire 

dollar loss

(in millions)

2017 262,759 1,601 6,436 4,870

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

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

Source: USFA, 2017 to 2019 NFIRS.

Nonresidential buildings

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

the NFIRS from 2017 to 2019.

Table 5. Nonresidential building fires and losses reported to the NFIRS (2017-2019)

Year Nonresidential 

building fires

Nonresidential 

building fire 

deaths

Nonresidential 

building fire 

injuries

Nonresidential 

building fire 

dollar loss

(in millions)

2017 73,340 62 666 3,010

2018 73,454 69 665 2,434

2019 75,714 79 704 2,335

Source: USFA, 2017 to 2019 NFIRS.

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

the NFIRS from 2017 to 2019. On average, 92% of nonresidential structure fires, 92% of 

deaths, 95% of injuries and 85% of dollar losses reported to the NFIRS from 2017 to 2019 

occurred in nonresidential buildings.

Table 6. Nonresidential structure fires and losses reported to the NFIRS (2017-2019)

Year Nonresidential 

structure fires

Nonresidential 

structure fire 

deaths

Nonresidential 

structure fire 

injuries

Nonresidential 

structure fire 

dollar loss

(in millions)

2017 79,290 68 688 3,099

2018 79,380 74 710 2,547

2019 81,891 86 752 3,507

Source: USFA, 2017 to 2019 NFIRS.
6 Data Sources and National Estimates Methodology Overview

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 

(2017-2019)

Year Residential 

building fires

Residential 

building fire 

deaths

Residential 

building fire 

injuries

Residential 

building fire 

dollar loss — 

adjusted to 

2019 dollars

(in millions)

2017 371,500 2,695 10,825 8,132

2018 379,600 2,790 11,525 8,343

2019 354,400 2,830 12,625 7,867

Source: USFA, Fire Estimate Summary Series (2010 to 2019).

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

(2017-2019)

Year Nonresidential 

building fires

Nonresidential 

building fire 

deaths

Nonresidential 

building fire 

injuries

Nonresidential 

building fire 

dollar loss — 

adjusted to 

2019 dollars

(in millions)

2017 111,000 95 1,200 2,836

2018 103,600 85 1,025 2,705

2019 110,900 100 1,125 2,870

Source: USFA, Fire Estimate Summary Series (2010 to 2019).

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 2019 national estimates of residential and 

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

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

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

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

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

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

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.

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

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.

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.
Data quality / Unknown data entries and missing values 9

Data quality

Data quality is an area of great importance. The following 3 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 3 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 

3 criteria before the data are released in the NFIRS Public Data Release 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 3 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

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, 50% of fatal fires 

in residential buildings reported from 2017 to 2019 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.

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

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 2017 to 2019; another 18.5% of reported 

fires had unknown causes. Thus, the percent of fires that had their cause reported was 

100 minus 18.5, which equals 81.5%. 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 81.5, which equals 50.8%.

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.

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 2017 to 

2019, 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 area of fire origin and factors 

contributing to ignition data elements which reflect larger increases in unknown values 

from 2017 to 2019.
Incomplete loss reporting 11

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

building fires reported to the NFIRS (2017-2019)

Data element

2017 2018 2019

Percent 

unknown

Percent 

unknown

Percent 

unknown

Area of fire origin 14.2 14.8 15.1

Heat source 39.5 39.9 40.3

Item first ignited 40.1 41.3 41.8

Factors contributing to ignition 31.6 32.9 34.4

Presence of detectors 31.3 31.1 30.1

Presence of AES 9.5 9.6 9.5

Fire cause 18.2 18.5 18.8

Source: NFIRS.

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

building fires reported to the NFIRS (2017-2019)

Data element

2017 2018 2019

Percent 

unknown

Percent 

unknown

Percent 

unknown

Area of fire origin 18.8 19.0 20.0

Heat source 43.5 43.6 44.3

Item first ignited 45.2 45.8 47.2

Factors contributing to ignition 33.6 34.8 36.3

Presence of detectors 20.2 20.9 20.1

Presence of AES 10.8 11.4 10.9

Fire cause 36.9 36.4 36.9

Source: NFIRS.

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.
12 Data Sources and National Estimates Methodology Overview

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.

“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 13

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. (2004). Fire data analysis handbook (2nd ed.). http://www.usfa.

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