In　order　to　clarify　the　incendivity　of frictional　sparks　from　light　alloys　in　metbane－air　mixture，a　laboratory scale　experlment　has　been　carried　out，using a drop－type　testing　apparatus　by　which light　alloy　samples　made　an impact　on　a　msted　steel　plate．丁he　effect　of　some　practical　conditions　on　the　incendivity　of　frictional　sparks　ware examined，changing　kinds　of　light　alloys，impact　conditions　and　the impact　energy．As　a　result，probability　of ignition　greatly　affected　on　the　impact　condltions，i．e，the　dropping　height and　the　weight　of　samples・The　impact energy　required　to　obtain 50 percents　probability　of　ignition　can　be　used　as　an index　for　estimating　the　incendivity of　light　alloys，Some　correlation　between　the　incendivity　and　content　of　magnesium　was　found　for　three　kinds　of light　alloys，The　incendivity　of　ligkt　a110ys　became　bwer　when　a　small　quantity　of　beryllium　was　added　to　Mlg base　lig且ht　alloys，but　clear　deαease　of　the　incendivlty　was　not　observed　as for　Al－Si　type　light　alloy．

Cyclic　Ioading　tests　of　the　cored　rock　were　performed　in　orde to　estlmate　the　geo－stress　of the　rocks．In　these tests，Acoustlc　Emission（AE）in　rocks　and　strains　of　the　surface　of　rocks　were　measured．In　only　one　loading test，Kaiser　effect　isn’t　always　dear，but　Kaiser　effect　becomes　clear in　cyclic　loading. In　this　AE　method，we　can get　not　only　the　value　of　the　axlahnitial　stress，but　also　the　maxlmum　stress．Differential　rate　method　can　also gives　us　these　two　value　as　same　as　AE　method　in　cyclic loading　test．Cored　rocks　were　sampled　at　the（iepth　of 117 to 173 meters　from　the　surface in granite　at　Chubu district．In　these　tests　four　AE　transducers　and four　strain gages　were　attached　on　the　surface　on the　rocks　in　order　to　estimate the　initial－geostress．The　obtained　results were　as　follows：

1）The　value　of　the　axial　stress　of　coreδrocks　wkich　corresponds　to　the　vertical　geo－stress　estlmated　by　AE and　DR　method　were　about2．65MPa，about2，60MPa，respectively， 2）　　It　can　be　concluded　that　the　vertical　geo stress　in　this　area has　a　strong　effect of the　weight　of　the　overlying rock． 3）　Estimated　lateral　maxlmum　geo stress　was　twlce　as　much　as　vertlcal　geo stress.

High－pressure facilities treat a lot of fiammable and／or toxicgas. Each facility is situated in various surroundings. So　far　it　runs　mainly　the　assessment　based　on　the　species　and　quantity　of　gas　of　their　own　holdings　to　estimate　a　potential risk of explosion or toxication inside the individual facility．However，it is requested to add the item of surroundings to the　subject　of　the　assessment　because　of　crowding　around　the　facility．

This paper proposes a new procedure based on the fuzzy logic to make a risk extent comparison with any facilities that are　difference　in　the　gas　holdlngs　and　surmundings．　And　it　illustrates　the　strength of　the　potential　hazard，the　probability of each strength and the method of calculation. Moreover，the procedure is applied to two virtual facilities to demonstrate the process of calculating the stricken strength of their hazards.