NBSIR 77-1217

Safety Problems Associated

with Pressure Containers

S. K. Wakamiya and N. J. Calvano

Product Engineering Division

Institute for Applied Technology

March 1977

Report to Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland

NBSIR 77-1217

SAFETY PROBLEMS ASSOCIATED

WITH PRESSURE CONTAINERS

S. K. Wakamiya and N. J. Calvano

Product Engineering Division

Institute for Applied Technology

March 1977

Report to Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland

\<Vy ‘'•j.u •»

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

Table of Contents

Page

Introduction 1

Fire Extinguishers 1

General Description 1

National Electronic Injury Surveillance System

(NEISS) Data 2

In-depth Investigations 4

Other Data 5

Safety Standards 8

Discussion 12

LP Gas Containers 13

General Description 13

NEISS Data 14

Death Certificates 14

In-depth Investigations 14

Safety Standards 16

Discussion 21

Conclusions 25

Appendix 27

Acknowledgments 37

References 38

Safety Problems Associated with Pressure Containers

Introduction

The objective of this study was to develop preliminary engineering

data needed to assess the adequacy of present standards for pressure

containers. This study was limited to LP Gas containers and fire

extinguishers since other pressurized containers such as aerosols and

carbonated beverage bottles are addressed in other CPSC programs. This

project addressed two tasks. The first task involved the review and

analysis of the injury data related to pressure containers. The second

task consisted of the review and critique of existing standards.

The injury data for this study was obtained from two sources, the

National Electronic Injury Surveillance System (NEISS) and the CPSC indepth epidemiological reports. The NEISS data was useful in obtaining a statistical sampling of the types of injuries related to pressure

containers. The in-depth epidemiological reports enabled identification of

accident patterns and hazards associated with the products.

Standards related to the design and maintenance of fire extinguishers

and LP gas containers were analyzed. Relationships between the hazards

identified in the injury data and the engineering issues from the standards

are discussed in this report.

Fire Extinguishers

General Description

Fires involving different combustibles require different methods of

extinguishment. Manufacturers have responded to this problem by producing

extinguishers effective against the various types of fires. Advances in

fire technology have resulted in improvement of old designs and

introduction of new types of extinguishers, while many original designs

have stayed in service. Thus, a wide variety of extinguishers are in use today

The earliest type of commercial fire extinguisher still in use at

present, is the soda acid extinguisher. This type of extinguisher is not

pressurized until activated by inverting the container. An acid and base

solution mix and react to form carbon dioxide which generates pressure

forcing water out through a hose 1

. For obvious reasons, this type of

extinguisher is also referred to as " invert-to-oper ate" . This type of

extinguisher is effective against fires involving wood, paper, rubber and

many plastics.

^References appear at the end of the report, following the appendix.
Another example of an early extinguisher is the type employing carbon

tetrachloride as an extinguishing agent. Some carbon tetratrachloride

extinguishers are still in service today; however, due to toxicity problems

the vast majority of them have been replaced by the more compact and

effective chemical extinguishers.

The foam extinguisher, another older type of extinguisher still used

today, operates by mixing a base salt solution with an acid salt solution,

producing a frothy agent which cools and smothers the flames. Such

extinguishers are effective against liquid fires, and if non-conductive

agents are used, against fires involving energized electrical equipment.

Foam extinguishers, are becoming relatively uncommon due to the trend

toward dry chemical extinguishers.

Most modern extinguishers contain agents such as carbon dioxide, dry

chemicals and liquified gases. Agents used commonly in dry chemical

extinguishers are sodium bicarbonate, potassium bicarbonate, ammonium

phosphate and potassium chloride. Chlorobromomethane and

bromotrifluoromethane are examples of liquified gas extinguishing agents.

NEISS Data

The NEISS data collected during the 4 year period beginning fiscal

year 1973 and ending fiscal year 1976 show that 177 injuries involving fire

extinguishers were treated at the 119 hospital emergency rooms on the NEISS

system.

Review of the NEISS matrix report enabled identification of the number

of each type of injury relative to the total number of injuries.

Lacerations (36%) were the most commonly occurring injury followed by

contusions (21%) and fractures (12%). Chemical burns, dermatitis, and

poisoning were diagnosed in 7%, 5%, and 4% of the injuries, respectively.

The mean severity value* of these injuries was 40 indicating a moderate

degree of injury. On a scale of 1 through 8 used by NEISS to categroize

the severity of injuries, a severity value of 40 would fall between

categories 4 and 5 as shown in Table 1. Examples of the type of injuries

which would fall under each category is also included in this table.

The mean severity value for fire extinguishers, when compared to the

average of the mean severity for all products monitored by NEISS, is lower

than average.

*In calculating mean severity, the number of cases in each severity

category is first multiplied by the appropriate severity value for

that category. The products of these multiplications are summed and

then divided by the total number of reported cases for that product code.

2
Table 1 Severity* Mean *

Severity

Category Examples of Injuries in Each Category

1 Mild injuries to small areas, for example, sprained foot

2 Contusion to lower trunk; dislocated arm, hand puncture,

non-hospitalized poisoning

3 Arm fracture, sprained neck

4 Finger crushing, head laceration, punctured eye

5 Concussion, fractured neck, ingested foreign object

6 Amputation, anoxia, arm crushing, hospitalized poisoning

7 All hospitalized category 6's 8 All deaths

* Incomplete or otherwise not acceptable data are assigned a severity value of 0

and are net included in calculations of mean severity.

i

Severity

Value

*

10

12

17

31

51

340

2,516

2,516

*This table was reproduced from NEISS flews, Volume 4, No. 1,

Consumer Product Safety Commission, July 1975.

3
In-depth Investigations

The CPSC’s Bureau of Epidemiology had on file 14 in-depth

investigations related to fire extinguishers. These reports covered a four

year period beginning fiscal year 1973 and ending fiscal year 1976. A

tabulation of the description, reported cause, and number of the incidents

appear in Table 2.

Table 2

Summary of Incidents

Description of incident Reported Cause // of cases

Explosion of container Interior corrosion 8

of extinguisher shell

Gage separation Weak attachment of gage 1 to extinguisher

Product failed to operate Malfunction under normal use 1

Contact with toxic Misdirection of spray 2 or caustic subtances

Asphyxiation Inhalation of toxic fumes 1

Consumer complaint Dealer refused to service 1 product

Explosions of fire extinguishers were cited in 8 of these in-depth

reports. One particular model of foam extinguisher supplied by one

manufacturer accounted for 7 of these 8 explosion incidents. In one of

these cases the extinguisher exploded inside a kitchen closet, damaging the

interior of the cabinet. In another case involving the same model

extinguisher, the explosion of the extinguisher occurred on top of a kitchen counter, where it had been stored for 3 years, and injured the

occupant who happened to be in the area at the time of the explosion. The

victim suffered a laceration requiring two stitches behind her left ear. Another investigation reported an explosion of the same model extinguisher

in the rear passenger compartment of a station wagon. None of these three cases apparently involved misuse of the product.

4
In another explosion incident, a 25 year old male was killed

instantaneously when the soda acid extinguisher he was holding exploded.

The explosion occurred several seconds after the activation of the

extinguisher, propelling a section of the container upwards and striking

the victim in the jaw.

There were two incidents associated with plastic pressure gage

assemblies on dry chemical extinguishers. In one case the plastic pressure

gage on a dry chemical extinguisher blew off discharging its contents. The

extinguisher was mounted on the inside wall of a camper at the time of the

incident. The other investigation regarding a pressure gage problem was

the result of a consumer complaint filed with CPSC. The dealer reportedly

refused to recharge a dry chemical fire extinguisher, claiming that the

plastic gage "was hazardous".

Other Data

Some in-depth investigation reports were particularly useful in

identifying sources of further information, such as persons to contact, and

literature related to the product.

A telephone conversation with a representative of the manufacturer

whose foam extinguishers accounted for 7 of the 8 explosion cases,

identified the cause of these accidents as a materials problem. The

contents of the extinguisher caused corrosion of the shell of the

container, weakening the shell over a period of years, resulting in an explosion. The manufacturer had issued a voluntary recall on its 1970

model year extinguisher in August 1974.

Evidently, corrosion of the inside of the container is a problem which

can occur in various types of extinguishers and is not limited to foam

types. Literature published by the National Fire Equipment Distribution in

1970 cites examples of water, foam, dry chemical and carbon ^ioxide

extinguishers which have exploded due to internal corrosion. -

The literature also pointed out the explosive hazards of the soda-acid

extinguishers, especially those with stainless steel shells and urged a phase out of these extinguishers. According to NAFED, the hydrostatic

failure rates are very high for soda acid extinguishers with stainless

steel shells. The following statistics were published in the NAFED

literature: 1) 22% of soda acid extinguishers failed the first 5 year

hydrostatic test, 2) 8% failed the second 5 year retest, and 3) 15 to

40% failed the third 5 year retest.

In addition to the NAFED literature, three other sources caution

against soda acid extinguishers.

5
1. A telephone conversation with the Fire Marshall's office in Salt Lake

City, Utah revealed that 8 to 10% of the state owned soda-acid

extinguishers failed the hyrostatic test in 1975. In comparison the

hydrostatic failure rate of dry chemical extinguishers, according to the

same source, was less than 1%.

2. A report authored by NBS scientists provided one explanation for the

high rate of failure of invert-to-operate extinguishers. According to that

paper, the stainless steel alloys commonly used in the body of these

extinguishers are particularly susceptible to intergranular corrosion.

Such corrosion may be caused by corrosive fluids such as sulfuric acid used

in invert-to-operate extinguishers.

3.

The NFPA Handbook of 1976 points out the dangers associated with the use of invert-to-operate extinguishers1

. The handbook states that the

failure rates of these extinguishers are alarmingly high. Furthermore, the

potential failures are not usually evident until the time of operation or hydrostatic test, because the extinguisher is not pressurized during

storage. The normal pressure in these extinguishers, when activated, is

about 687 kPa (100 psi) but when a blockage of the hose occurs, such as by

kinking, the pressure may reach 2060 kPa (300 psi).

Invert-to-operate extinguishers have many important operational

disadvantages when compared to modern extinguishers1. Some of these are 1)

high electrical conductivity of the contents 2) high inspection,

maintenance and recharging cost and 3) potentially dangerous to use.

Additional information regarding the plastic gages on chemical

extinguishers was obtained from the telephone conversation with a representative of the Fire Marshall's office in Salt Lake City, Utah. The

office has on file two reports of incidents of plastic gages separating

from the extinguishers; one of these was also the subject of a CPSC indepth report. Additionally, the office reportedly has received 30

complaints from consumers concerning these extinguishers. Fire

extinguisher servicing companies in the Salt Lake City area have received

about 100 complaints involving plastic gages, according to the Fire

Marshall’s office. The majority of the complaints reportedly involved

extinguishers made by two companies. The complaints usually stemmed from

premature loss of pressure in the extinguisher

.

A conversation with the Chief of the NBS Fire Service provided an explanation for the problems associated with the plastic gages on some dry

chemical extinguishers. These extinguishers reportedly will normally hold

charging pressure when new, but after servicing, they have a marked

tendency to develop a leak from the gage. Evidently there is great

difficulty in applying the proper amount of torque when reinstalling the

plastic gages after servicing the extinguisher. If too much torque is used

when tightening the gage, subsurface cracks may occur at the neck of the

6
gage; too little torque will result in a loose attachment of the gage.

Either of these conditions could result in pressure leakage or separation

of the gage from the extinguisher body.

7
Safety Standards

The standards relevant to the safety of fire extinguishers are listed

in Table 3 with descriptions of the contents of each standard. Review of

these standards indicated that in general they appear to be adequate.

The Code of Federal Regulations, and UL Standards 154, 299, and 626

provide specifications to prevent rupture of extinguisher shells during

normal use and under some misuse conditions. The UL 154 refers to the Code

of Regulations section 178 for cylinder strength specifications. According

to these specifications, the cylinder should not rupture at pressures up to

about 3 times its normal charging pressure at 21°C (70°F). UL 299 and UL

626 specify that rupture pressure shall be no less than (1) four times the

charging pressure at 21°C for a metallic container or (2) six times for a non-metallic container.

Maintenance requirements to detect deterioration of the extinguishers

which have been in service are covered by NFPA 10A and CGA-6. The

maintenance requirements in the NFPA standard consist of the hydrostatic

test which is summarized in Tables 4 and 5. The CGA-6 covers visual

inspection methods of extinguisher shells to detect corrosion which may

make continued use of the extinguisher unsafe.

The safety factors for rupture stress and maintenance requirements

should be sufficient to prevent rupture of an extinguisher even if

subjected to some degree of overpressurizing, provided that it has been

designed to resist corrosion and has been maintained properly.

The only apparent weakness in these standards stems from the lack of

tests to insure the compatibility of the extinguishing agent and propellant

with the extinguisher shell to prevent corrosion of the shell. UL 299 and

626 require that the shell be resistant to corrosion, but no tests are specified. It is apparently assumed that a manufacturer knows which alloys

used for extinguisher shells are susceptible to corrosion by certain

extinguishing agents. However, incidents reported in the in-depth

investigations seem to indicate that such an assumption cannot be made.

The review of UL 299 revealed some rigorous tests to insure that the

pressure gage is attached securely to the extinguisher container assembly.

One of the tests is a One Year Time Leakage Test in which extinguishers are charged with expellant gas at normal room temperature and checked for

leakage during a 1 year period. The pressure leak is not to exceed the

rate which would cause the pressure to drop below the lower limit of the

operable range in 1 year. Other tests for checking attachment of pressure

gages to the extinguisher shell are drop tests and accelerated aging tests

for plastic parts. In the drop tests two samples of extinguishers are dropped from a height of 91.4 cm (3 feet) in the horizontal, upright and

upside down positions for a total of three drops for each extinguisher.

Generally, each extinguisher is positioned so that when dropped, its

8
weakest point will be contacted upon impact. After these tests, each

extinguisher is hydrostatically tested.

Table 3

Standards for Fire Extinguishers

Standard

Code of Federal Regulations

Title 49, Transportion,

Part 178

Compressed Gas Association

CGA Pamphlet C-6,

Standards for Visual Inspection

Underwriters Laboratories UL 154,

Safety Standards for Carbon Dioxide

Fire Extinguishers

UL 299 Safety Standards for Dry

Chemical Fire Extinguishers

UL 626 Safety Standards for

2 1/2 Gallon Stored Pressure

Water-Type Fire Extinguishers

UL 711 Safety Standards for

Rating and Fire Testing of

Extinguishers

National Fire Protection Association

NFPA 10, Standard for Installation

of Portable Fire Extinguishers

NFPA 10A, Recommended Practice

for Maintenance and Use of

Portable Fire Extinguishers

Contents

Construction specifications,

compliance tests and requirements

for cylinders shipped interstate

Visual inspection method for

detecting corrosion in cylinder

for compressed

Requirements for construction

operation, and tests for CO^

extinguishers, exclusive oi fire

performance tests.

Same coverage as above except

applies to dry chemical extinguishers

Same coverage except applies to

Water-type stored pressure

extinguishers

Rating and classification of fire

extinguishers and related test

procedures.

Installation requirements for

extinguishers.

Maintenance and use of

extinguishers, including hydrotesting requirements and test

procedures.

9
Table 4

Hydrostatic Test Pressure

Requirements (Note 1)

Soda-acid

Foam

Cartridge operated water

Original factory test pressure* as shown

on nameplate

Carbon dioxide extinguishers

Carbon dioxide and nitrogen cylinders

(used with wheeled extinguishers)

5/3 service pressuref

stamped on cylinder

Carbon dioxide extinguishers with

cylinder specification ICC3 3,000 psi

All stored pressure and

Bromochlorodifluoromethane (1211)

Factory test pressure not to exceed 2 times

the service pressure Carbon dioxide hose assemblies 1,250 psi

Dry chemical and dry powder hose

assemblies 300 psi

* The factory test pressure is the pressure at which the shell was tested

at time of manufacture. This pressure is shown on the nameplate. f

The service pressure is the normal operating pressure as indicated on the gage and nameplate.

(Note 1) Table reproduced from the NFPA Handbook 1976.

10
Table 5

Hydrostatic Test Interval

for Extinguishers (Note 1)

Test Interval Extinguisher Type (years) Soda acid 5 Cartridge operated water and/or antifreeze 5 Stored pressure water and/or antifreeze 5

•Vetting agent 5

c oam 5 Loaded stream 5

Cry chemical with stainless steel shells or soldered brass shells 5 Carbon dioxide 5

Dry chemical, stored pressure, with mild steel

shells, brazed brass shells, or aluminum

shells 12

Dry chemical, cartridge operated, with mild

steel shells 12

Dromotrifluoromethane—Halon 1301 12

Sromochlorodifluoromethane—Halon 1211 12

Dry powder, cartridge operated, with mild

steel shells* 12

* Except for stainless steel and steel used for compressed ejas cylinders, all other steel sholls ate defined as "mild steel " shells.

1 (Note 1) Table reporduced from the NFPA Handbook 1976.

11
Discussion

NEISS data provides a statistical data bank on types of injuries

associated with fire extinguishers and other consumer products.

Lacerations, contusions and fractures accounted for 69% of all fire

extinguisher injuries treated at hospital emergency rooms, while chemical

burns, poisoning and dermatitis were associated with only 16% of the cases. This suggests that most injuries were probably caused by either 1) fire

extinguisher or a component part striking the victim, 2) victim struck by some object while holding a fire extinguisher. Thus, it appears that the

major injury mechanism associated with fire extinguishers is mechanical in

nature rather than chemical. While the NEISS data does not allow

determination as to whether or not the preponderance of mechanical injuries was a result of faulty extinguishers, it does reveal that toxicity of the

extinguishing agent is not a commonplace hazard of extinguishers.

The review of in-depth reports and other data revealed accident

patterns associated with fire extinguishers. Incidents apparently were

caused by the fault of the product in 10 of the 14 cases. This study

revealed three problems needing attention associated with safety of fire

extinguishers. These were internal corrosion, plastic pressure gages and use of obsolete extinguishers.

Fire extinguishers safety standards appear to address most safety

problems adequately. However, none of the standards reviewed included a test to insure the compatibility of the contents with the extinguisher

shell. Although the hydrostatic tests specified by NPFA 10A and the visual

inspection test for corrosion outlined in CGA C-6 may detect internal

corrosion and possible loss of structural integrity of the container after

the extinguisher has been in service, a severe deterioration of the

extinguisher shell could occur before the product is due for such tests.

The 7 incidents cited in the in-depth reports involving explosions of one

particular make of extinguisher exemplify such a situation. All of the

explosions in those incidents occurred between two and three years after

purchase of the extinguishers and at least 2 years before any in service

tests were due.

Although the attachment of the plastic pressure gage on some dry

chemical extinguishers seemed to be a problem as evidenced by data

collected during this study, the review of the Dry Chemical Standard UL 299

revealed some tests to insure that the method of attachment of the gage

results in a good seating and strong connection between the gage and the

container body. After these tests each extinguisher is hydrostatically

tested. An aging test which involves the exposure of the plastic parts to

temperature of 100°C (212°F) for 180 days is also conducted to check

possible degradation of plastic parts. These tests should preclude the

12
certification of new extinguishers with inferior plastic pressure gage

attachments. However, as indicated on page 6 of this report, these plastic

gages are apparently very difficult to reinstall properly after servicing

the extinguisher.

Although only one case involving a soda acid extinguisher was reported

in the in-depth investigations, other sources (i.e., NAFED literature and

the NFPA Handbook) indicate high failure rates and hazards associated with

use of these extinguishers. The NFPA Handbook of 1976 states that "several

million" invert-to-operate type extinguishers are still in service, with

soda-acid types accounting for 85%.

LP Gas Containers

General Description

Liquefied Petroleum (LP) is a major source of heating and cooking

energy in rural areas unserviced by gas mains. Additionally, LP gas is

used as a fuel source by numerous campers and trailers because of the

portability of LP gas powered ovens and ranges. According to Peet , nine

million consumers relied on LP gas as a fuel source for heating and cooking

in 1970.

Although there are several types of LP gases (such as isobutane,

propylene, butylenes and mixtures of these hydrocarbons), propane and

butane are the most extensively used LP gases

5

. Propane and butane are mixed in various ratios, depending on the climate, to take advantage of the

desirable qualities of both gases

0

. LP gases are normally odorless;

therefore, mercaptan, a compound having a disagreeable odor, is often added

to these gases to facilitate detection in the event of a leak.

In operation the LP gas cylinder is partially filled with liquefied

gas in equilibrium with a vapor occupying the space above the liquid. When

the valve on the cylinder is opened, some of the pressurized vapor leaves

the tank. Some of the gas in the liquid state immediately evaporates to

maintain equilibrium, thus always keeping the pressure inside the cylinder

constant with constant temperature regardless of the fluid level. The

t of that gas or

Thus, since

906 kPa (132

psig) and 117 kPa (17 psig)', respectively, the pressure in the tank

containing these gases will be between these two extremes, depending on the

mixture of these two gases. At a temperature of 54°C (130°F) the same tank

would have a pressure somewhere between 474 kPa (69 psig) and 2060 kPa (300

psig) 7

.

LP gas tanks, usually cylindrical in shape, are produced in various

sizes ranging from 17.8 cm (7 in) in diameter by 48.2 cm (19 in) in length

pressure in the LP gas tank is equal to the vapor pressjjr

mixture of gases stored in the tank at that temperature,

propane and butane have vapor pressures at 21°C (70°F) of

13
to 47.0 cm (18.5 in) in diameter by 137 cm (54 in) in length. ^ These tanks

normally contain 9.1 kg (20 lbs) to 45.5 kg (100 lbs) of gas.

NEISS Data

According to the NEISS data, 154 injuries associated with LP gas tanks

and fittings were treated at NEISS hospital emergency rooms from fical year

1973 to fiscal year 1976. The most commonly occurring injury was thermal

burns, averaging 38% of all injuries over the four year period.

Lacerations (12%), and contusions and abrasions (10%) were other

frequently occurring injuries.

For fiscal year 1976 the mean severity index of injuries associated

with LP gas containers was 263* as compared to the average mean severity of

101 for the product group "General Household Appliances" consisting of 23

products.

Death Certificates

CPSC had on file 105 death certificates related to LP gas tanks and

fittings as of June 1976. By comparison the total number of death

certificates for all products monitored by CPSC was 128,744.

Explosions involving LP gas containers accounted for 64 deaths of

which 12 were attributed to tank explosions. There were 30 deaths due to

inhalation of gas fumes. The death certificates did not state whether or not the involved products were defective. The other 11 deaths occurred in

incidents which could not be categorized under specific accident patterns.

In-depth Investigations

Review of the 31 in-depth investigations covering the period March

1967 through October 1975 identified leakage of gas from the LP gas tanks

and fittings as the primary hazard. Explosions of the gas fumes occurred

in 23 incidents.

The appendix of this report contains summaries of the 31

investigations.** Table 6 lists the nature of the incident, its reported

cause, and the number of such incidents.

*See Table 1 for examples of injuries which would have a severity index

of 263.

**Summaries of the in-depth reports for incidents occurring between March

1967 and June 1973 were reproduced from the CPSC Hazard Analysis on LP

Gas, 19748

.

14
Table 6

Summary of LP Gas Container Incidents

Type of incident

Explosion

Explosion

Explosion

Explosion

Explosion

Inhalation of gas

fumes

Other incidents not involving defective containers or fittings 8

Total 31

Gas leaks occurred in 20 of the 31 investigated incidents. In all but one of those cases, the gas fumes from the leak were ignited by a source of

a flame or spark such as a water heater or a match. The LP gas container was cited as the source of the leak in 7 investigations. The location of

the leak on the container was identified in only 2 instances. In both of

these incidents the valve was apparently the source of the leak. Review of

the other 5 reports did not indicate whether the gas leak was from the

container body or from the valve.

In one of the incidents caused by leakage of gas, a LP gas container

stored in the back of a van developed a leak from its valve. The victim

opened the vents and doors of the van for ventilation and repaired the

leak. He waited 3 to 5 minutes to let the fumes escape. An explosion

occurred when he pushed the ignition button on the van's heating unit.

In another case the victim heard a hissing noise coming from the

garage where a butane tank was stored. As he was removing the leaking tank

from the garage, an explosion occurred. The force of the explosion

propelled the victim through the side door of his garage and through the

side of the neighbor's garage. Evidently, the water heater flame ignited

Reported Cause Number of cases

Gas leak from tank; ignition 7

by spark or flame

Gas leak from fuel line; 7

ignition by spark or flame

Gas leak from unknown source; 6

ignition by spark or flame

Overpressurization; rusted container; 1 no safety relief valve

Undetermined l

Leak; no explosion 1

15
the gas fumes causing an explosion according to the investigation report.

The leak was apparently caused by the safety relief which may have opened,

since the outside temperature was close to 38°C (100°F) at the time of the

accident.

There were three incidents where poor installation or maintenance were apparently involved. A non-leaking LP gas container exploded in one of

these incidents. High temperature during a warm day evidently

overpressurized the container. Lacking a safety relief valve, the

container exploded. Inspection of the tank after the accident revealed

that its interior was corroded. According to the investigative report the

tank had been refilled only three or four days before the accident.

Poor installation was the probable cause for a leak in one incident.

A gas leak developed in a 0.953 cm (3/8 inch) copper fuel hose where it

rubbed against the side of a camper. Vibrations apparently wore a hole

through the line.

In another case where poor installation or maintenance was suspected,

a man was seriously injured in a explosion, which occurred in a trailer

when he struck a match to light a cigarette. The force of the explosion

blew apart the top and sides of the trailer. A new tank of propane had

been installed a few days before the accident.

Safety Standards

The standards relevant to the safety of LP gas containers, listed in

Table 7, were reviewed.

According to NFPA 58, LP gases are to be stored in containers built

under either the Department of Transportation (DOT) specification, which

are contained in the Code of Federal Regulations title 49, or manufactured

in conformance to the ASME Pressure Vessel Code. The Code of Federal

Regulations state that LP gas containers shipped interstate must meet DOT

specifications.

16
Table 7

Standards for LP Gas Containers

Compressed Gas Association Standards:

CGA Pamphlet S-l.l

Safety Relief Device Standards

Part 1 - Cylinders for Compressed Gases

CGA Pamphlet C-6

Standard for Visual Inspection

of Compressed Gas Cylinders

National Fire Protection Association Standard

NFPA 58, (ANSI Z106.1)

Standard for Storage and Handling

of Liquified Petroleum Gases

Code of Federal Regulations

Title 49, Transportation

Parts 171 to 190 DOT Cylinder Specifications

American Society of Mechanical Engineers

ASME Pressure Vessel Code Section VIII

Division 1

Underwriters Laboratories:

UL 125, Valves for

Anhydrous Ammonia and

LP-Gas (other than safety relief)

UL 132, Safety Relief

Valves for Anhydrous

Ammonia and LP-Gas

UL 144, Pressure Regulating

Valves for LP-Gas

UL 644 Container Assemblies

for LP-Gas

17
Strength of LP Gas Containers

The DOT Cylinder Specifications prescribe the service pressure or range of service pressures for which a cylinder built under a particular

specification may be used. The service pressure represents the highest

pressure to which the tank will normally be subjected during

transportation, storage or use. The service pressure for LP gas containers

is based on the higher of the two vapor pressures of the gas in the

container at two temperatures as follows:

a) The pressure in the container at 21°C (70°F) must be less than

the service pressure.

b) The pressure in the container at 54°C (130°F) shall not exceed

5/4 times the service pressure.*

DOT containers for LP gases are hydrostatically tested at a pressure

at least 5/3 times the service pressure and must exhibit permanent

volumetric expansion less than 10% of the total volumetric expansion at

test pressure. Used tanks are hydrostatically tested at 2 times the

service pressure for requalification.

The LP gas containers built under the ASME code have a 4:1 safety

factor.** The design pressure of the container is determined by the vapor

pressure at 38°C (100°F) of the gas to be stored in the tank as shown in

Table 8. Since commercial propane has a vapor pressure of 1410 kPa (205

psi) at 38°C a tank containing this gas must have a design pressure of at

least 1720 kPa (250 psig) . Thus, considering the 4:1 safety factor, the

rupture pressure of a tank containing commercial propane will theoretically

be at least 6870 kPa (1000 psig).

*For example, the minimum required service pressure for a tank containing

commercial propane is 1648 kPa (240 psig), since the vapor pressure of

commercial propane at 21°C (70°F) and 54°C (130°F) are 906 kPa (132 psig)

and 2060 kPa (300 psig), respectively. (5/4 x 1648 kPa = 2060 kPa)

**Safety factor is the ratio of the ultimate strength of the metal to the

design stress.

18
Table 8

Minimum Design Pressure for ASME Containers (Note 1)

For Gases with Vapor Minimum Design Pressure in

Pressure in psig at 38°C psig ASME Code, Section VIII

( 100°F) not to exceed Division 1, 1974 Edition

80 100 (Note 2)

100 125

125 156

150 187

175 219

215 250

215 312 (Note 3)

(Note 1) This table reproduced from NFPA 58

(Note 2) New containers for 100 psig design pressure are not authorized after Dec. 1947.

(Note 3) Tanks installed on vehicles require higher relief

valve settings.

It is apparent from the preceding discussion concerning the strength

of LP gas containers, that both the DOT and ASME containers should

withstand the vapor pressure of the stored gas even at high temperatures

(up to at least 38°C) if the container is not corroded or in some other way

structurally weakened.

Examination and Requalification

All LP gas tanks must be periodically tested and requalified by

methods prescribed in the Code of Federal Regulations part 173.34 e(10).

The purpose of such tests is to detect and dispose of containers which have

been structurally weakened due to corrosion, dents, gouges, or exposure to

fire, or normal deterioration with age.

19
A new container must be requalified within 12 years after the date of

manufacture. Subsequent reclassifications are required after 5, 7 or 12

years depending upon the requalification method used. Containers may be

reclassified using one of three methods prescribed by the Code of Federal

Regulations:

1) Water jacket type hydrostatic test. A pressure of two times the

service pressure is applied and the volumetric expansion of the

cylinder is recorded. If the container leaks or if permanent

volumetric expansion exceeds 10% of the total expansion, the container

is rejected. Containers rejected because of leaks may be repaired by

a facility approved by DOT and the Bureau of Explosives. Containers

requalified by this method must be retested in 12 years.

2) A hydrostatic test.

A pressure of two times the service pressure is applied, but

volumetric expansion of the tank need not be measured. The container

is carefully observed while pressurized for sign of leak, bulging or swelling. This test qualifies the cylinder for 7 years.

3) Recorded Visual examination.

A visual examination of the cylinder by a competent person, using CGA

C-6 as a guide, may be conducted to requalify a container for 5 years.

Containers which exhibit leaks, excessive dents, gouging or corrosion

must be scrapped or repaired as in item 1) above.

Container Appurtenances

Container appurtenances, as defined by NFPA 58, are safety relief

valves, regulator devices, container shutoff valves, plugs, liquid level

gages and pressure gages. The design, fabrication and operation of these

appurtenances are covered by CGA S-l.l, NFPA 58, ASME Code, UL 125, UL 132,

and UL 144.

In general requirements for these appurtenances appear to be

satisfactory. Tests are outlined in these standards to check gasket

materials for compatibility with the LP gas. Corrosion resistant coatings

are specified for ferrous parts which, when corroded, will interfere with

the operation of valves. Tests for leakage from these appurtenances are

also specified.

20
Safety Relief Valve Settings

Although the requirements for the design, fabrication and operation of

safety relief valves appear to be adequate, the pressure at which the

safety relief is set to operate on ASME containers causes some concern. As

shown in Table 9 the safety relief valves on ASME tanks may be set to open

at the lower limit of 88% of the design pressure of the container. Thus,

the safety reliefs on propane tanks may open when tank pressure (which is

equal to the vapor pressure of the stored gas) reaches 220 psig. Based on information from NFPA 58, the vapor pressure of propane would be 220 psig

at temperatures between 41°C (105°F) and 43°C (110°F). This means that

venting of the gas can occur at temperatures which are not uncommon in many

parts of the U.S.

Since the LP gases are highly flammable, it seems undesirable to vent

the gas at a pressure so close to the design pressure of the tank in view

of the fact that the ASME tanks have a safety factor of 4:1.

The problem just mentioned does not exist for LP gases with very low

vapor pressures such as butane. This is because ASME containers must not

have a minimim design pressures less than 860 kPa (125 psig), as shown in

Table 9. Thus, as shown, the pressure relief setting for butane tanks is

much higher than the vapor pressure of the gas even at temperature as high

as 54°C (130°F).

The containers built under DOT specifications use much higher pressure

relief settings than the ASME containers. Table 10 indicates that the low

limit specified by NFPA 58 for opening of the safety relief valve is 2470

kPa (360 psig) for tanks containing commercial propane. Thus even at 54°C

(130°F) no venting of the gas will occur. Although the tank pressure at

this temperature would be 2060 kPa (300 psig), the tank should withstand

that pressure since these tanks are hydrostatically tested at 3300 kPa (480

psig)

.

It appears that the pressure relief settings prescribed for DOT

containers would be more effective in preventing unwanted gas leaks due to

venting in comparison to the valve settings recommended for ASME

containers.

Discussion

The injury data and death certificates reviewed during this study

indicate that there may be a significant risk of serious accidents

associated with the use of LP gas containers. During the last four years

NEISS hospital emergency rooms treated 154 injuries related to this

product, with a mean severity index of 263* (See Table 1 for the

relationship between seriousness of injuries and its severity index.) CPSC

21
Design

Pressures

and

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Relief

Operating

Pressures

for

ASME

Specification

Tanks

Containing

Commercial

Propane

and

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22

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S23
had on file 105 death certificates related to LP gas containers. By

comparison the total number of death certificates on file for all products

monitored by CPSC was 128,744.

The analysis of the in-depth investigation reports and the death

certificates revealed that explosions were responsible for most of the

injuries and deaths. The fact that thermal burns, lacerations, contusions

and abrasions accounted for 60% of all LP gas container injuries cited by

NEISS supports the argument that explosion is the major problem with these

products.

Gas leakage was reported to be the primary cause of these explosions.

In 20 of the 31 investigated incidents explosions occurred when leaking gas

was ignited by a flame or a spark. The source of the leak was identified

as the tank in only 7 instances.

Standards related to the design and maintenance of LP gas containers

were reviewed. The analyses of the standards in general indicated adequacy

of the requirements: There is no obvious explanation for the large number

of leaks cited in the in-depth reports and numerous explosions described in

the death certificates. However, two requirements in the reviewed

standards raises some questions.

One of the questionable provisions in the standards deals with the

requalification of used LP gas cylinders. As noted on page 19 of this

report, DOT allows the use of three methods for requalifying cylinders for

continued service. One of these methods, the visual inspection method

appears to be much less rigorous than the other two. Although this

inspection is to be performed according to Compressed Gas Association

Standard CGA-6, a standard widely accepted by industry, visual inspections

tend to be rather subjective.

An apparent deficiency in the standards concerns the low setting of

the start-to-discharge pressure of the safety relief valves used on ASME

containers as described on page 21. This could cause an unnecessary

release of the flammable LP gas at elevated atmospheric temperatures.

Thus, it is possible that some gas leaks described in the in-depth reports

where high atmospheric temperatures were involved may have been due to

containers having pressure reliefs with a low setting.

Other causes of the LP gas accidents appear to involve poor

maintenance and installation as evidenced by 3 in-depth reports. In one of these incidents where rupture of a container occurred, inspection of the

container after the incident revealed that its interior was rusted. (See case 750325 BEP 7010 in the Appendix.) Furthermore, the safety relief

valve, required by Federal Regulations, was missing from the container at

the time of the accident. Since the container was filled only 3 or 4 days

24
before the accident and since NFPA 58 requires that the container be

inspected before it is filled, it appears that this incident may have been

prevented if requirements of the Federal Regulations and NFPA 58 were

followed.

Many LP gas accidents could apparently be prevented if gas leaks, the

major cause of these accidents, could be detected and reported immediately

to a gas company or to qualified service personnel. Only 3 of the

investigated cases stated that the victims smelled gas fumes prior to the

explosions. In 9 cases the victims denied smelling the odor of gas.

Apparently the addition of mercaptan to LP gas to facilitate detection of

leak is ineffective in many instances.

Some accidents occurred even when the gas leaks were detected by the

victims. In these cases the victims allegedly repaired the leaks, and

allowed the fumes to escape. Explosions occurred when victims struck

matches to relight pilot lights or to light cigarettes.

The number of LP gas accidents probably would be reduced by the

introduction of a more positive method of detecting leaks and by education

of consumers as to the proper action to take when a leak is suspected. One

possibility may be to install gas detectors in areas where gas is likely to

accumulate in the event of a leak.

Conclusions

Fire Extinguishers

Data collected during this study suggests that modern fire

extinguishers appear to be relatively safe if used and maintained properly.

However, the following problem areas were noted:

1) Internal corrosion of the container due to incompatibility between

the container and its contents. UL 299 and UL 626 have no tests to

check for such incompatibilities. Adoption of standard compatibility

tests should reduce the possibility of occurrence of corrosion related

incidents.

2) Method of attachment of pressure gages on dry chemical fire

extinguishers. The data gathered during this study does not clearly

indicate whether this problem is related to design or quality control.

UL Standard 299 covering the dry chemical extinguishers appears to

have requirements and tests to insure proper attachment of the gage

to the extinguisher. A study other than a literature search is

necessary to identify the cause of this problem.

3) Invert-to-operate extinguishers. Since the production of this

type of extinguisher was discontinued in the late 1960's, there are no current standards covering the design of these products. However, the

25
continued widespread use of this obsolete extinguisher despite its

poor safety record poses a safety problem. Although the exact

mechanism of failure of these extinguishers has not been proven, many

sources attest to the high failure rates and potential safety hazards

of these extinguishers. It appears that some efforts at curbing or eliminating the use of invert-to-operate extinguishers would be

desirable.

In general, (except as noted in item, 1) this study indicates that the

present standards related to the safety of fire extinguishers appear to be

adequate

.

LP Gas Containers

The injury data and death certificates studied in this report

indicates that a substantial number of serious accidents involving LP gas

containers have occurred. The NEISS data indicates that injuries

associated with LP gas containers tend to be much more severe in comparison

with injuries associated with general household appliances.

The following conclusions were made from this study:

1)

The low discharge pressure setting of safety reliefs used on ASME

containers, as discussed on p. 21 of this report, may be a safety

hazard if used in climates or in enclosed locations where ambient

temperatures above 41°C are likely.

2)

Based on this study, standards concerning the design, testing and

maintenance of LP gas containers appear to be adequate (except as noted in item 1).

3) The primary hazard associated with the use of LP gas appears to be

leakage from various parts of the system, including fuel lines,

fittings, and tanks. The in-depth reports in most cases did not

reveal the cause of development of a leak; however, there were

instances where poor maintenance and installation were suspected.

4) The number of LP gas accidents could probably be reduced by use of

a more positive means of detecting leaking gas and by consumer

education on the proper course of action to take when a gas leak is

suspected

.

26
APPENDIX

Case // Date of Accident Summary of Accident

A02561

4-8-73

The complainant and his family were traveling on

a highway in a van. He noticed that the heat output

from the propane heating unit was low, heard a hissing sound coming from it and smelled gas fumes.

He stopped the van and went to the rear of the van where the heat unit and one 20 lb bottle and one

4 lb bottle of propane were stored. At this time

the 20 lb bottle had been connected to the heater.

He noticed that the heater flame had gone out. He

disconnected the 20 lb bottle from the heating unit

and connected the 4 lb unit to the heater. After

opening the doors of the van and letting it air out

for 3 to 5 minutes, he lit a match to relight the

heater, when explosion of the fumes occurred. The

tanks had been refilled two or three months before

the accident.

A14548

11-18-73

The victim was driving a propane powered car home from

work. After driving for about ten minutes with all

the windows rolled up, he attempted to light a cigarette, when the explosion occurred. The force of

the explosion tore away the rear section of the car. Strangely, the propane tank located in the trunk was undamaged.

A13503

6-73

The victim heard a hissing sound coming from the

garage where two 5 gallon cylinders of butane gas were stored. After locating the cylinder which was the source of the noise, he attempted to carry it out of

the garage, when an explosion occurred. The flame

from the water heater inside the garge ignited the fumes

from the gas cylinder. The investigator attributed

the accident to a sticky safety relief. Since the

outside temperature was 98°F, this may have increased

the pressure inside the tank enough to activate

pressure relief. Normally, the pressure relief should

close automatically after pressure has been relieved,

but probably stuck on open position.

A21740

7-7-73

LP gas powered oven exploded, causing a fire and

damaging the oven. The cause of the explosion was

not stated nor apparent from the report.

27
A29522

3-25-73

A4U688

3-

31-73

A30079

4-

11-73

1974

750325 5EP7010

1-2-75

750105

2-13-75

Two persons riding in a vehicle noticed a leaking

propane gas tank. As they approached the tank, an explosion occurred. The leakage was apparently from

a hole in the tank. The gas fumes may have been

ignited by an ignition spark from the vehicle,

cigarette smoke, or a fire arm (a 22 rifle and a shotgun were found in the vehicle).

A water heater flame ignited fumes from a leaking

propane gas tank in the basement of a house.

Two children were playing with a small butane tank,

which the mother thought was empty. When the butane

tank was taken next to the water heater, an explosion

occurred, resulting in a fire.

Victim struck a match to light a propane gas range.

Explosion occurred immediately. Cause of this

accident was leakage due to poor installation. A

3/8 inch copper hose was used as a fuel line which

goes through the wall of a camper. Vibrations caused

the line to rub against the side of the camper wearing

a hole in the fuel line.

Propane gas tank exploded. "Atmospheric heat

apparently caused swelling of contents" according

to the in-depth report. The tank had been filled only

3 to 4 days before the accident. The interior of the

tank was rusted. Follow up with the manufacturer

indicated that the company has extensive quality control

procedures, including radiographic tests, hydrostatic

tests, and sampling methods. Manufacturer claims many

consumers fail to maintain cylinders properly. This

cylinder was built in 1964 and had no safety relief

valve. Manufacturer stated that all cylinders shipped

from his factory have pressure relief, but some people

replace them with valves with no relief valve for

economy.

When the victim lit a match while standing near a propane gas stove, inside a trailer, an explosion

occurred, blowing away the walls and top of the

trailer. A new tank of propane gas had been installed

outside the trailer a few days before the accident.

Source of leak unknown.

28
750214 ISU 5019

2-14-75

A propane gas stove caught fire. The gas flow

regulator in the stove stuck in the open position

allowing gas to flow to the pilot light at full

tank pressure. This apparently generated enough

heat to melt other components of the stove releasing

more gas.

750816 BEP 0021

8-10-75

A 14 year old male suffered a chemical burn to the

eye. While sniffing gas from a 10 lb propane tank,

his hand slipped releasing a blast of gas into his

eye.

751025 BEP 0015

10-19-75

A spherical LP gas camping tank fell from a storage

shell and rolled over victim's foot.

29
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Acknowledgments

The authors wish to thank Mr. Leonard Schachter of the Bureau of

Epidemiology at the Consumer Product Safety Commission for his great

assistance in obtaining injury data for this report. Also, Dr. B. W.

Christ of the Metallurgy Section at the National Bureau of Standards

was most helpful in suggesting sources of information related to the

safety of fire extinguishers. Finally, we wish to thank Mrs. Rosemary

Massengill for her diligent typing efforts.

37
References

1. McKinnon, G. P. and Tower, K., eds., Fire Protection Handbook,

14th edition, Section 16 National Fire Protection Association, 1976.

2. "Fire Extinguishers, Can They Be Dangerous", National Association

of Fire Equipment Distributors, 1970.

3. Christ, B. W. and Smith, J. H., Safety Evaluation of Soda Acid

Extinguishers , NBSIR 75-922, National Bureau of Standards, 1975.

4. Peet, L. J. and Picket, M. S., et al, Household Equipment, 6th ed.,

John Wiley and Sons, Inc. 1970.

5. Fetherston, F., Handbook of Compressed Gases , Compressed Gas

Association, Reinhold Publishing Co., 1966.

6. Denny, L. C. and Luxon L. L., Handbook of Butane and Propane Gases , Jenkins Publications, 1951.

7. Standard for the Storage and Handling of Liquefied Petroleum Gases , NFPA 58 National Fire Protection Association, 1974.

8. Hazard Analysis on Liquefied Petroleum Gas , U. S. Consumer Product

Safety Commission, 1974.

38
NBS-I 14A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NRSIR 77-1217

2. Ciov't Accession

No.

3. Recipient’s Accession No.

4 . TITLE AND SUBTITLE

SAFETY PROBLEMS ASSOCIATED

WITH PRESSURE CONTAINERS

5, Publ ication Date February 1977

6. Performing Organization Code

446.03

7. AUTHOR(S)

S.K. Wakamiya and N.J. Calvano

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4461430

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, MD 20016

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Accident reports from hospital emergency rooms and reports of interviews with

accident victims were reviewed to determine the probable causes of accidents

involving two types of pressure containers: fire extinguishers and liquefied

petroleum (LP) gas tanks. The data collected and reviewed during the study

suggests that some of the safety problems associated with fire extinguishers

involve: 1) incompatibility of the contents of an extinguisher with its

shell; 2) faulty method attachment of plastic pressure gages on some dry

chemical extinguishers; and 3) widespread use of obsolete extinguishers.

The primary hazard associated with LP gas containers appear to be leakage

from various parts of the LP system. In many instances leaking gas accumulated

in a closed area and was accidentally ignited, resulting in an explosion.

Engineering standards relevant to the safety of fire extinguishers and LP gas

tanks were reviewed. Although the present standards governing these pressure

containers address most safety problems adequately, a few of the requirements

in some of these standards appear to be of questionable value in preventing

certain types of accidents.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

Container; corrosion; explosion; extinguisher; fire; gas; injury; liquefied;

petroleum; standards.

18. AVAILABILITY [XX Unlimited

cz For Official Distribution. Do Not Release to NTIS

Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. Cl

fx~ Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

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(THIS REPORT)

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20. SECURITY CLASS

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21. NO. OF PAGES

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