nes 711 determination of the smoke index of the products of combustion from small specimens of...

Ministry of Defence Defence Standard 02-711 (NES 711)

Issue 1 Publication Date 01 April 2000

Incorporating NES 711 Category 2

Issue 2 Publication Date January 1981

Determination Of The Smoke Index OfThe Products Of Combustion From

Small Specimens Of Materials

DStan

DStan is now the publishing authority for all Maritime Standards (formerly NESs). Any reference to any other publishing authority throughout this standard should be ignored. Any queries regarding this or any other Defence Standard should be referred to the DStan Helpdesk as detailed at the back of this document.

AMENDMENT RECORD

Amd No Date Text Affected Signature and Date

REVISION NOTE

This standard is raised to Issue 1 to update its content.

HISTORICAL RECORD

This standard supersedes the following:

Naval Engineering Standard (NES) 711 Issue 2 dated January 1981.

Ministry of Defence

Naval Engineering Standard

NES 711 Issue 2 (Reformatted) January 1981

DETERMINATION OF THE SMOKE INDEX OFTHE PRODUCTS OF COMBUSTION FROM

SMALL SPECIMENS OF MATERIALS

This NES Supersedes

Record of Amendments

AMDT INSERTED BY DATE

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NAVAL ENGINEERING STANDARD 711

ISSUE 2 (REFORMATTED)

DETERMINATION OF THE SMOKE INDEX

OF THE PRODUCTION OF COMBUSTION

FROM SMALL SPECIMENS OF MATERIALS

The issue and use of this Standard

is authorized for use in MOD contracts

by MOD(PE) Sea Systems and

the Naval Support Command

ECROWN COPYRIGHT

Published by:

Director of Naval ArchitectureProcurement Executive, Ministry of DefenceSea Systems, Foxhill, Bath BA1 5AB

NES 711Issue 2 (Reformatted)

iii

SCOPE

1. This NES gives details of one of a series of test methods for determining the combustioncharacteristics of materials. The test explores the smoke production potential of a smallsample of material under specified conditions of pyrolysis and combustion. It does notnecessarily indicate the smoke production under other thermal exposure conditions.

2. The test is useful for the quality control of materials and for research and development. Itmaybe used to compare the combustion characteristic of a series of materials. Combustioncharacteristics tests alone are not suitable for assessing the total fire hazard of products butmay be used to specify a quality of a raw material or product.

3. The method is based on that developed by the American National Bureau of Standards anddescribed by Gross D, Loftus J J and Robertson A F in ASTM Special Technical PublicationNo 422, 166−204(1967), but modifications have been incorporated as a result of work carriedout at AMTE (Dockyard Laboratory), Portsmouth.

NOTE. STP No 422, 166−204(1967) is superseded by ASTM E662:1979 Specific OptionalDensity of smoke generated by solid materials.


iv


v

FOREWORD

Sponsorship

1. This Standard is sponsored by the Procurement Executive, Ministry of Defence, ShipDepartment, Section D 123a, Foxhill, Bath BA1 5AB.

2. This Naval Engineering Standard (NES) is to be applied as required by any ProcurementExecutive, Ministry of Defence contract for determining the Smoke Index of the products ofcombustion from small specimens of materials.

3. If this Standard is found to be technically unsuitable for any particular requirement thesponsor is to be informed of the circumstances with a copy to Ship Department Section D191a.

4. Any user of this Standard either within MOD or in outside industry may propose a change toan NES. Proposals for changes which are:

a. not directly applicable to a particular contract are to be made to the sponsor or the NES

b. directly applicable to a particular contract are to be dealt with using existingdepartmental procedures or as specified in the contract.

5. No alteration is to be made to this publication except by the issue or a formal change.

6. Unless otherwise stated, reference in this Standard to approval, approved, authorized andsimilar terms means by the Procurement Executive, Ministry of Defence, Director GeneralShips.

Conditions of Release

General

7. This Naval Engineering Standard (NES) has been prepared for the use of the Crown and ofits contractors in the execution of contracts for the Crown. The Crown hereby excludes allliability (other than liability for death or personal injury) whatsoever and howsoever arising(including but without limitation, negligence on the part of the Crown, its servants or agents)for any loss or damage however caused where the NES is used for any other purpose.

8. This document is Crown Copyright and the information herein may be subject to Crown orthird party rights. It is not to be released, reproduced or published without written permissionof the MOD.

9. The Crown reserves the right to amend or modify the contents of this NES without consultingor informing any holder.

MOD Tender or Contract Process

10. ThisNES is the property of the Crown and unless otherwise authorized in writing by theMODmust be returned on completion of the contract, or submission of the tender, in connectionwith which it is issued.

11. When this NES is used in connection with aMOD tender or contract, the user is to ensure thathe is in possession of the appropriate version of each document, including related documents,relevant to each particular tender or contract. Enquiries in this connection may be made ofthe local MOD(PE) Quality Assurance Representative or the Authority named in the tenderor contract.


vi

12. When NES are incorporated into MOD contracts, users are responsible for their correctapplication and for complying with contracts and any other statutory requirements.Compliance with an NES does not of itself confer immunity from legal obligations.

Related Documents

13. In the tender and procurement processes the related documents listed in each section andAnnex A can be obtained as follows:

a. British Standards British Standards Institution,389 Chiswick High Road,London W4 4AL

b. Defence Standards Directorate of Standardization and Safety Policy,Stan 1, Kentigern House, 65 Brown Street,Glasgow G2 8EX

c. Naval Engineering Standards CSE3a, CSE Llangennech, Llanelli,Dyfed SA14 8YP

d. Other documents Tender or Contract Sponsor to advise.

Note: Tender or Contract Sponsor can advise in cases of difficulty.

14. All applications to Ministry Establishments for related documents are to quote the relevantMOD Invitation to Tender or Contract Number and date, together with the sponsoringDirectorate and the Tender or Contract Sponsor.

15. Prime Contractors are responsible for supplying their subcontractors with relevantdocumentation, including specifications, standards and drawings.

Health and Safety

Warning

16. ThisNESmay call for the use of processes, substances and/or procedures thatmay be injuriousto health if adequate precautions are not taken. It refers only to technical suitability and inno way absolves either the supplier or the user from statutory obligations relating to healthand safety at any stage of manufacture or use. Where attention is drawn to hazards, thosequoted may not necessarily be exhaustive.


vii

CONTENTSPage No

TITLE PAGE i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCOPE iii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FOREWORD v. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Sponsorship v. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Conditions of Release v. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General v. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .MOD Tender or Contract Process v. . . . . . . . . . . . . . . . . . . . . . . . . .

Related Documents vi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Health and Safety vi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Warning vi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONTENTS vii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 1. APPLICATION 1.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 2. PRINCIPLE 2.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 3. APPARATUS 3.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.1 Test Chamber 3.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.2 Timer 3.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.3 Chart Recorder 3.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 4. TEST SPECIMENS 4.1. . . . . . . . . . . . . . . . . . . . . . . . . .4.1 Sheet or Film Materials 4.1. . . . . . . . . . . . . . . . . . . . . . .4.2 Mounting of Specimen 4.1. . . . . . . . . . . . . . . . . . . . . . . .4.3 Insulated Wires 4.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.4 Conditioning 4.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 5. SAFETY OF OPERATORS 5.1. . . . . . . . . . . . . . . . . . .

SECTION 6. PROCEDURE 6.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 7. CALCULATION 7.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.1 Correction of Results 7.1. . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 8. REPORT 8.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .FIGURE 8.1 DETAILS OF TYPICAL BURNER 8.2.

ANNEX A RELATED DOCUMENTS A.1. . . . . . . . . . . . . . . . . . . .

ANNEX B DEFINITIONS AND ABBREVIATIONS B.1. . . . . . . .

ALPHABETICAL INDEX


viii


1.1

1. APPLICATION

a. The method has been found suitable for testing materials in the form of sheet(up to 25mm thick) or film, and as wire and cable insulation and sheathingextruded on electrical conductors. It should not beused alone for the descriptionor appraisal of the fire hazard of a material or product under actual fireconditions.


1.2


2.1

2. PRINCIPLE

a. A material is exposed to specified standard thermal conditions of pyrolysis andcombustion in a continuous procedure. The change in optical density of thesmoke produced when dispersed within a fixed volume of air is recordedthroughout the period of the test. The resulting density/time curve is used tocalculate the Smoke Index.


2.2


3.1

3. APPARATUS

3.1 Test Chamber

a. The apparatus required is known as the National Bureau of Standards (NBS)smoke density test chamber and is briefly described as a closed chamberapproximately 900mmhigh, 900mmwide and 600mmdeep inwhich a specimen75mm ¢ 5mm ¢ thickness as supplied (up to 25mm maximum) is supportedin a frame, with a face in a vertical plane, and exposed to heat and then flame.In setting up the smoke chamber the exhaust blower outlet must be connectedby hose to an exhaust hood or vent to ensure that on completion of a test theproducts of combustion formed do not contaminate the laboratory atmosphere.These gases can be toxic to personnel.

b. The heat source is an electric furnace adjusted to give a heat flux of 2.5 wattsper square centimetre at the specimen surface. A vertical collimated light beamis employed through the full height of the chamber with a photo multipliermicro photometer system to measure the transmittance of light.

c. A full description of the apparatus is given in ASTM STP No 422 but differs inthis method in the following respects:

(1) Mixing Fan. A small fan shall be positioned centrally near the top of thechamber to ensure complete dispersion of the smoke homogeneouslythroughout the chamber.

(2) Auxiliary Heater. A small black heater is positioned centrally in thechamber and is used only to reduce the time delay in reaching operatingtemperature.

(3) Burner.Amulti-jet burner constructed as shown in FIGURE 8.1 shall beused with premixed air/natural gas fuel. The burner shall be centred infront of the specimen holder level with bottom edge of the specimen and10mm away from it. The air and natural gas shall be metered usingcalibrated rotameters, the rate being such that a blue flame is obtainedwhich touches the specimen over 90% of its width at a heightapproximately 5mmabove its bottom edge. It shall be so arranged that theburner can be ignited remotely without having to open the chamber.

3.2 Timer

a. A timing device measuring intervals up to at least 20 minutes and accurate towithin ±1s shall be used.

3.3 Chart Recorder

a. A chart recorder set to operate with a full scale deflection of 50mV, is connectedto the output from the micro photometer to provide a continuous record of thechange of % transmittance with time during a test run.


3.2


4.1

4. TEST SPECIMENS

4.1 Sheet or Film Materials

a. At least 3 specimens shall be cut from the material under test. The dimensionsshall be 75mm ¢ 75mm utilizing the natural thickness of the material exceptwhere it exceeds 25mm, inwhich case the material shall be reduced in thicknessto 25mm by cutting away the face not required to be tested.

4.2 Mounting of Specimen

a. Cut a sheet of heavy duty aluminium foil (approx 0.04mm thick) to a size whichwill permit overlapping of the sample face on all four sides by approximately6mm. Place the sample in the centre of the foil and fold excess over the edgesand against the face to be tested. Place the wrapped sample into a sample holderso that the face to be tested is exposed. Place an insulating block against thesample, insert the tension spring and locking pin, taking care not to compressflexible samples below their normal thickness. Without cutting the face of thesample, carefully remove any exposed foil.

4.3 Insulated Wires

a. Each specimen for test shall comprise fifteen 75mm lengths of the insulatedwire, cut from the bulk coil. The specimen shall be fabricated by placing thespecimen holder, test face down, on to a flat surface and positioning each 75mmlength in the holder in a parallel arrangement so that when the holder is in thetest position the wires will be vertical.

b. An insulating block 10mm thick completely wrapped in aluminium foil is placedon top of the wires followed by a tension spring and locking pin. The wires areheld in place by the pressure of the insulating block on the ends of the wiresagainst the lip of the sample holder. When assembled in this mannerapproximately 1m of wire is exposed for test. Three such specimens shall beprepared for an evaluation of one material.

c. If the diameter of the wire is greater than 5mm, then less than 15 lengths willbe used and due account taken of the shorter total length.

4.4 Conditioning

a. Unless otherwise agreed, all test specimens shall be conditioned at 23° C ± 2°Cand 50 ± 5% RH for at least 24h prior to testing.


4.2


5.1

5. SAFETY OF OPERATORS

a. When the following test is being carried out, there is a risk that flammableand/or toxic fumes will be given off from the specimen under test. Operators areto take adequate precautions to avoid exposure to the evolved fumes.


5.2


6.1

6. PROCEDURE

a. These instructions relate specifically to the NBS Smoke Density Test Chamberas modified in accordance with Clauses 3.1c.

b. Switch on the power to the chamber, chart recorder, internal fan and auxiliaryheater.

c. Ensure that the ‘FLAME GAS’, ‘RADIOMETER AIR’ and ‘FLAME AIR’ togglevalves are shut. Turn on gas and air supplies.

d. Close ‘VENT’ and ‘INLET VENT’ on the chamber.

e. Ensure optical shutter on the photomultiplier box is in the OUT position, turnon ‘LINE’ and ‘LAMP’.

f. Set the photomultiplier photometer to ON.

g. Switch on ‘HEATER’ and set ‘HEATERVOLTSADJUST’ control to 30%. Afterabout five minutes reset to 60%, then to 90% after a further five minutes.

h. When a chamber wall temperature of 35° C is attained, shown on the‘CHAMBER TEMPERATURE’ meter, switch the auxiliary heater OFF.

i. Set the photomultiplier photometer to HV.

j. Set the chart recorder to 50 mV full scale deflection.

k. Calibrate the photomultiplier photometer as follows:

(1) Clean the lower and upper optical windows with soft tissue moistenedwith alcohol.

(2) Set ‘MULTIPLIER’ switch to 0.1.

(3) Set ‘BLANK ADJUST’ to LOW.

(4) Set ‘DAMPING’ to OFF.

(5) Depress ‘FINE ADJUST’ control and rotate clockwise two full turns.

(6) Adjust the ‘BLANK ADJUST FINE’ control until meter indicates 0%relative intensity (transmittance). Set the chart recorder pen to zero.

(7) Reset ‘MULTIPLIER’ switch to 100 and ‘DAMPING’ to ON, depress‘FINE ADJUST’ control and rotate anti-clockwise until a slight stop isreached (about 2 full turns).

(8) Open photomultiplier tube shutter by depressing the black rod on thephotomultiplier box to the IN position.

(9) Depress ‘FINE ADJUST’ control and rotate until meter indicates 100%transmittance. Set the chart recorder pen to 100.

l. Set the ‘HEATER VOLTS’ control to the pre-determined voltage to obtain anoutput of 2.5W/sq cm (refer to furnace calibration in NBS method).

m. Open the ‘INLET VENT’ and the chamber is ready for use.

n. After half a minute, to allow the furnace to reach the correct output, place theloaded sample holder on the support rods directly in front of the furnace.


6.2

o. Immediately start the chart recorder drive, shut door of chamber and close the‘INLET VENT’ (a convenient chart speed is 10mm/minute).

p. After five minutes open the ‘FLAME GAS’ and ‘RADIOMETER AIR’ togglevalves. Adjust the auxiliary flowmeter to give a gas flow of 500ml per minute.Adjust the air input to 18 on the ‘RADIOMETER AIR’ flowmeter.

q. Operate the remote ignition device switch until the flame ignites.

r. Continue the run for a further fifteen minutes, or until a minimum %transmittance value is reached.

s. If at any time the transmittance value falls below 10% change the multiplierswitch to 10; if the transmittance again falls below 10% of full scale, change themultiplier switch to 1. A further drop to below 10% of full scale will require themultiplier switch to be changed to 0.1. Oncompletion of the test the switchmustbe reset to 100 before the maximum clear beam transmittance value Tc can beobtained.

t. After the total time of 20minutes close the ‘FLAME GAS’ and ‘RADIOMETERAIR’ toggle valves, slide the sample away from the front of the radiant panel andreduce the ‘HEATER VOLTS ADJUST’ control to 50%.

u. Evacuate the chamber by opening the ‘VENT’ and ‘INLET VENT’. (NoteLaboratory ventilation fan should also be run.)

v. After complete evacuation of the chamber obtain a new maximum clear beamtransmittance value on the chart recorder, this reading being designated as thevalue Tc.

w. For testing of replicates or freshmaterials on the same day restart at Clause 6.k.


7.1

7. CALCULATION

a. Because of the progressive build-up of deposits on the optical windows duringa test run, the recorded transmittance values are artificially depressed. It istherefore necessary to apply a correction to the results before calculating theSmoke Index. This is carried out by constructing a new plot of thetransmittance/time relationship as described below.

7.1 Correction of Results

a. Using the trace obtained from the chart pen recorder, identify the followingvalues:

Tc—clear beam transmittance at end of test

Tmin—minimum transmittance obtained during test

Convert Tc and Tmin to equivalent specific optical Density, DSc and DSmax.

b. The conversion of % transmittance to specific optical density for theNBSsmokedensity chamber is given by:

Specific Optical Density (Ds) = 132 log100T

where T = % transmittance

c. Subtract DSC from DSmax to obtain corrected maximum specific optical densityDSmax C. Convert DSmax C to % transmittance and plot this value on the penrecorder chart as the corrected minimum transmittance at the same timeinterval as Tmin.

d. If DSC is 3% or less of DSmax no further correction to pen recorder trace need bemade; if more than 370, correct remainder of trace in the following mannerwhen transmittances less than 70% have been recorded:

Convert 70% transmittance to specific optical density (ie 20).

Correct the 70% transmittance point on the trace by the formula

20 − DSCDSmax

× 20; convert this value back to % transittance and plotat the same time interval as the uncorrected 70% transmittance.

e. If transmittances less than 40% have been recorded, correct the 40%transmittance (53 specific optical density) by the formula:

53 − DSCDSmax

× 53; convert this value back to % transmittance and

plot at the same time interval as the uncorrected 40% transmittance.

f. If transmittances less than 10%have been recorded, correct in the samemanneras for 70% and 40% transmittances shown above.

g. Construct a new curve of transmittance/time using the corrected values oftransmittance obtained.

h. The Smoke Index is calculated in the following manner:


7.2

(1) If the minimum transmittance value is greater than or equal to 70%,

Smoke Index =Ds at Tmintmin

(2) If the minimum transmittance value is less than 70%,

Smoke Index =Ds at T70t70

+Ds at T40t40

+Ds at T10t10

+Ds at Tmin (X–Tmin)

(x–y)

tmin

Where:

DS at T70 = specific optical density corresponding to 70%transmittance

DS at T40 = specific optical density corresponding to 40%transmittance, etc

t70 = time (in minutes) from start of test to reach 70%transmittance

t40 = time (in minutes) from start of test to reach 40%transmittance

x = lowest transmittance reference value reached duringtest, ie either 70%, 40% or 10%

y = next lower transmittance reference value to x, ieeither 40%, 10% or 0%

i. The Smoke Index for a material shall be the mean of the calculated smokeindices for at least 3 replicates.


8.1

8. REPORT

a. The report shall include the following:

(1) A reference to this Standard

(2) A full description of the material

(3) The Smoke Index of the material

(4) Description of any unusual behaviour during the test eg melting anddripping.

(5) The following statement:

‘This test result alone does not assess the fire hazard of thematerial or aproductmade from this material under actual fire conditions. Consequently the resultsof this test alone shall not be quoted in support of claims with respect to the firehazard of thematerial or product under actual fire conditions. The results whenused alone should only be used for research and development, quality controland material specifications.’


8.2

FIGURE 8.1 DETAILS OF TYPICAL BURNER


A.1 ANNEX A

ANNEX A.

RELATED DOCUMENTS

A.1 Reference is made to:

Referred to inClause

American Society for Testing Materials Special TechnicalPublication 422 166−204 (1967)

Scope 3., 3.c.

Do. E662 :1979 Scope 3.

ISO 3261—Fire tests, Vocabulary Annex B.


A.2ANNEX A


B.1 ANNEX B

ANNEX B.

DEFINITIONS AND ABBREVIATIONS

B.1 For the purpose of this Standard the following definitions apply:

Combustion See ISO 3261

Pyrolysis See ISO 3261

Smoke Index The numerical summation of the rates ofchange in specific optical density of thesmoke produced from the start of the test to70% 40% 10% and minimum lighttransmittance values.


B.2ANNEX B


INDEXINDEX.1

ALPHABETICAL INDEX

AAir volume, 2.1

Auxiliary heater, 3.1

BBlock—insulating, 4.1

Burner, 3.1

CCalculations, 7.1

Chart recorder, 3.1, 6.2, 7.1

Collimated light beam, 3.1

Combustion—characteristics tests, iii

Combustion—definition, 2.1, B.1

Conditioning, 4.1

Correction of results, 7.1

DDensity of smoke, 2.1

EExhaust blower outlet, 3.1

FFire hazard, 1.1

Flammable/toxic fumes, 5.1

Foil—aluminium, 4.1

Furnace—electric, 3.1

GGases—toxicity, 3.1

HHeat—flux, 3.1


INDEX INDEX.2

MMaterials—sheet/film, 4.1

Method, iii

Mixing fan, 3.1

Mounting of specimen, 4.1

OOptical density, 2.1

PPhoto multiplier, 3.1

Pin—locking, 4.1

Precautions, 5.1

Pyrolysis, iii, B.1

QQuality control, iii

RReport content, 8.1

Rotometers, 3.1

SSample holder, 4.1

Smoke chamber, 3.1

Smoke density test chamber, 3.1, 6.1

Smoke index, 2.1, 7.1, 7.2, B.1

Specimens—number and sizes, 4.1

Spring tension, 4.1

TTest chamber, 3.1

Test materials, 1.1

Timer, 3.1

WWire diameter, 4.1

wires insulated, 4.1

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Revision of Defence Standards

Defence Standards are revised as necessary by up issue or amendment. It is important thatusers of Defence Standards should ascertain that they are in possession of the latest issue oramendment. Information on all Defence Standards is contained in Def Stan 00-00 Standardsfor Defence Part 3 , Index of Standards for Defence Procurement Section 4 ‘Index of DefenceStandards and Defence Specifications’ published annually and supplemented regularly byStandards in Defence News (SID News). Any person who, when making use of a DefenceStandard encounters an inaccuracy or ambiguity is requested to notify the Directorate ofStandardization (DStan) without delay in order that the matter may be investigated andappropriate action taken.

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